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Leaf internal diffusion conductance limits photosynthesis more strongly in older leaves of Mediterranean evergreen broad-leaved species
Abstract
Leaf age-dependent changes in structure, nitrogen content, internal mesophyll diffusion conductance (gm), the capacity for photosynthetic electron transport (Jmax) and the maximum carboxylase activity of Rubisco (Vcmax) were investigated in mature non-senescent leaves of Laurus nobilis L., Olea europea L. and Quercus ilex L. to test the hypothesis that the relative significance of biochemical and diffusion limitations of photosynthesis changes with leaf age. The leaf life-span was up to 3 years in L. nobilis and O. europea and 6 years in Q. ilex. Increases in leaf age resulted in enhanced leaf dry mass per unit area (MA), larger leaf dry to fresh mass ratio, and lower nitrogen contents per dry mass (NM) in all species, and lower nitrogen contents per area (NA) in L. nobilis and Q. ilex. Older leaves had lower gm, Jmax and Vcmax. Due to the age-dependent increase in MA, mass-based gm, Jmax and Vcmax declined more strongly (7- to 10-fold) with age than area-based (5- to 7-fold) characteristics. Diffusion conductance was positively associated with foliage photosynthetic potentials. However, this correlation was curvilinear, leading to lower ratio of chloroplastic to internal CO2 concentration (Cc/Ci) and larger drawdown of CO2 from leaf internal air space to chloroplasts (ΔC) in older leaves with lower gm. Overall the age-dependent decreases in photosynthetic potentials were associated with decreases in NM and in the fraction of N in photosynthetic proteins, whereas decreases in gm were associated with increases in MA and the fraction of cell walls. These age-dependent modifications altered the functional scaling of foliage photosynthetic potentials with MA, NM, and NA. The species primarily differed in the rate of age-dependent modifications in foliage structural and functional characteristics, but also in the degree of age-dependent changes in various variables. Stomatal openness was weakly associated with leaf age, but due to species differences in stomatal openness, the distribution of total diffusion limitation between stomata and mesophyll varied among species. These data collectively demonstrate that in Mediterranean evergreens, structural limitations of photosynthesis strongly interact with biochemical limitations. Age-dependent changes in gm and photosynthetic capacities do not occur in a co-ordinated manner in these species such that mesophyll diffusion constraints curb photosynthesis more in older than in younger leaves.
... Evergreen tree species with long leaf lifespan retain several cohorts of foliage that can contribute significantly to canopy photosynthesis (Niinemets et al. 2005, Warren 2006, Peguero-Pina et al. 2007, Yasumura and Ishida 2011. Indeed, Escudero and Mediavilla (2003) analyzed the decline in photosynthetic performance of several evergreen species from Mediterranean-type climates with long lifespan, concluding that the retention of old leaves resulted in a higher whole-canopy net CO2 assimilation, despite their lower assimilation rate. ...
... including Mediterranean evergreen tree species during aging and senescence (Niinemets et al. 2005(Niinemets et al. , 2006. In fact, gm plays a predominant role in the photosynthetic process of Mediterranean evergreen tree species, being often the most limiting factor for net CO2 ...
... Values of gm for a given plant species can be influenced by different leaf anatomical traits, mainly the cell wall thickness, the mesophyll and chloroplast surface area exposed to intercellular air space per unit leaf area (Sm/S and Sc/S, respectively) and the chloroplast size (Terashima et al. 2011, Tomás et al. 2013, Peguero-Pina et al. 2016b, 2017b, Sáez et al. 2017, 2018, Carriquí et al. 2019. Given the strong control of leaf anatomy on gm, Niinemets et al. (2005) suggested that the drawdown of photosynthesis and gm in older leaves of Mediterranean evergreen tree species could be associated with increases in the thickness of mesophyll cell walls with increasing leaf age. Moreover, Niinemets et al. (2009) proposed that the dismantling of the photosynthetic apparatus associated to leaf senescence would reduce Sc/S, which could explain the reduction of both gm and net CO2 assimilation. ...
Leaves of Mediterranean evergreen tree species experience a reduction in net CO2 assimilation (AN) and mesophyll conductance to CO2 (gm) during aging and senescence, which would be influenced by changes in leaf anatomical traits at cell level. Anatomical modifications can be accompanied by the dismantling of photosynthetic apparatus associated to leaf senescence, manifested through changes at biochemical level (i.e., lower nitrogen investment in photosynthetic machinery). However, the role of changes in leaf anatomy at cell level and nitrogen content in gm and AN decline experienced by old non-senescent leaves of evergreen trees with long leaf lifespan is far from being elucidated. We evaluated age-dependent changes in morphological, anatomical, chemical and photosynthetic traits in Quercus ilex subsp. rotundifolia Lam., an evergreen oak with high leaf longevity. All photosynthetic traits decreased with increasing leaf age. The relative change in cell wall thickness (Tcw) was less than in chloroplast surface area exposed to intercellular air space (Sc/S), and Sc/S was a key anatomical trait explaining variations in gm and AN among different age classes. The reduction of Sc/S were related to ultrastructural changes in chloroplasts associated to leaf aging, with a concomitant reduction in cytoplasmic nitrogen. Changes in leaf anatomy and biochemistry were responsible for the age-dependent modifications in gm and AN. These findings revealed a gradual physiological deterioration related to the dismantling of the photosynthetic apparatus in older leaves of Q. ilex subsp. rotundifolia.
... The change in the resource investment and in the useefficiency along the leaf life span is an important way of recycling the nutrients and adapting to the environment (Silvertown et al. 1997). This can be especially so for evergreen plants, in which leaves produced along several years exhibit ample changes in morphology, nutrient concentrations, photosynthetic capacity and photosynthetic nutrient use efficiency (Sellin 2001;Niinemets et al. 2005;Li et al. 2009;Rodríguez-Calcerrada et al. 2012). For example, leaf mass per area (LMA) has been reported to increase with increasing leaf age (Sellin 2001;Mediavilla et al. 2011), whereas leaf N concentration and instantaneous photosynthetic N-use efficiency (PNUE) generally show an opposite trend (Sellin 2001;Niinemets et al. 2005;Rodríguez-Calcerrada et al. 2012). ...
... This can be especially so for evergreen plants, in which leaves produced along several years exhibit ample changes in morphology, nutrient concentrations, photosynthetic capacity and photosynthetic nutrient use efficiency (Sellin 2001;Niinemets et al. 2005;Li et al. 2009;Rodríguez-Calcerrada et al. 2012). For example, leaf mass per area (LMA) has been reported to increase with increasing leaf age (Sellin 2001;Mediavilla et al. 2011), whereas leaf N concentration and instantaneous photosynthetic N-use efficiency (PNUE) generally show an opposite trend (Sellin 2001;Niinemets et al. 2005;Rodríguez-Calcerrada et al. 2012). The probable reason for this result is that old (but not senescing) leaves of evergreen trees play a role in nutrient storage (Cherbuy et al. 2001;. ...
... In relation to these structural changes, a greater fraction of N remains allocated to cell walls, whereas N allocated to more easily degradable photosynthetic component decreases, which results in lower P n and lower PNUE in older, higher-LMA leaves (Dyckmans et al. 2002;Onoda et al. 2004;Takashima et al. 2004;Rodríguez-Calcerrada et al. 2012;Wyka and Oleksyn 2014). In addition, age-related structural changes can result in a longer path of CO 2 diffusion from stomata to mesophyll cells and chloroplasts (Parkhurst 1994;Hanba et al. 1999;Niinemets et al. 2005). ...
eedle experience large variations in photosynthetic rates in response to cone presence and needle aging. Exploring the interaction effect of these factors on photosynthetic traits is helpful to understand the source-sink relationship between needles and cones. Here, we examined the impact of needle age on needle CO2 assimilation rate (Pn), needle mass per area (LMA), and needle concentration of soluble sugars, starch, total non-structural car-bohydrates ([NSC]), nitrogen ([N]) and phosphorus ([P]) in cone‐bearing branches (repro-ductive branches) and branches without cones (vegetative branches) of Pinus koraiensis.We also compared instantaneous photosynthetic N-use efficiency (PNUE) and P-use effi-ciency (PPUE) in reproductive and vegetative branches. Our results showed that needles in reproductive branches had lower Pn, [N], [P], PNUE and PPUE than the needles in veg-etative branches, but higher [NSC] and LMA. The differences between branch types were similar across needle ages, despite a clear effect of aging on photosynthetic traits: Pn, [N], [P], PNUE and PPUE decreased with increasing needle age, whereas LMA increased and [NSC] did not change with needle age. Unexpectedly, these results suggest that Pn in nee-dles of reproductive branches is limited by NSC accumulation, and that N and P needed for cone development come from adjacent needles/reproductive branches while NSC come from more distant organs. These results shed light on the source-sink transport of carbon, N and P between needles and cones and are helpful for eventually predicting and improv-ing crop size in Pinus koraiensis.
... Photosynthetic rate (A) often has a strong positive correlation with mesophyll conductance (g m , the diffusion of CO 2 from substomatal cavities to the carboxylation sites in the chloroplasts; Barbour et al., 2010;Giuliani et al., 2013;Jahan et al., 2014;Xiong et al., 2016;Ellsworth et al., 2018;Knauer et al., 2019;Gago et al., 2020;Jahan et al., 2021) and decreased g m is considered to be one of the main factors involved in early age-induced photosynthetic decline (Niinemets et al., 2005;Flexas et al., 2007;Zhang et al., 2008). Conversely, Tosens et al. (2012) found g m and A increased, and the CO 2 drawdown from intercellular airspace to chloroplast (C i -C c ) decreased, with increasing leaf age in Populus tremula L. Whitehead et al. (2011) did not find leaf age effects between currentyear leaves and one-year old leaves on stomatal conductance (g sc ) and g m but there was a significant decline in g m with increasing tree height in Nothofagus solandrii var. ...
... The bar represents the average standard error, n = 5. et al. (2005)). The decline in A has sometimes been attributed to a decline in mesophyll conductance (g m ) in oak (Niinemets et al. (2005), and mustard (Monti et al. (2009)) which in some instances was due to changes in leaf anatomy including tobacco (Clarke et al., 2021), maple (Hanba et al. (2001) and poplar (Tosens et al. (2012)). However, other studies in pine report that g m limitations to A did not increase with leaf age (Warren (2006)) and in southern beech, g m itself was not significantly lower in mature compared to young leaves (Whitehead et al. (2011)). ...
statement: Mesophyll conductance ( g m ) was negatively correlated with wheat leaf age but was positively correlated with the surface area of chloroplasts exposed to intercellular airspaces ( S c ). The rate of decline in photosynthetic rate and g m as leaves aged was slower for water-stressed than well-watered plants. Upon rewatering, the degree of recovery from water-stress depended on the age of the leaves, with the strongest recovery for mature leaves, rather than young or old leaves. Diffusion of CO 2 from the intercellular airspaces to the site of Rubisco within C 3 plant chloroplasts ( g m ) governs photosynthetic CO 2 assimilation ( A ). However, variation in g m in response to environmental stress during leaf development remains poorly understood. Age-dependent changes in leaf ultrastructure and potential impacts on g m , A , and stomatal conductance to CO 2 ( g sc ) were investigated for wheat ( Triticum aestivum L.) in well-watered and water-stressed plants, and after recovery by re-watering of droughted plants. Significant reductions in A and g m were found as leaves aged. The oldest plants (15 days and 22 days) in water-stressed conditions showed higher A and gm compared to irrigated plants. The rate of decline in A and g m as leaves aged was slower for water-stressed compared to well-watered plants. When droughted plants were rewatered, the degree of recovery depended on the age of the leaves, but only for g m . The surface area of chloroplasts exposed to intercellular airspaces ( S c ) and the size of individual chloroplasts declined as leaves aged, resulting in a positive correlation between g m and S c . Leaf age significantly affected cell wall thickness ( t cw ), which was higher in old leaves compared to mature/young leaves. Greater knowledge of leaf anatomical traits associated with g m partially explained changes in physiology with leaf age and plant water status, which in turn should create more possibilities for improving photosynthesis using breeding/biotechnological strategies.
... To examine the accuracy of the LCC-based V cmax products used in this study, we first built an observational dataset of V cmax by compiling field measurements collected at nine sites covering four PFTs (i.e., DBF, EBF, ENF, and GRA) across Europe ( Figure 12) [127,[134][135][136][137][138][139][140][141]. Then, we compared the mean V cmax seasonality derived from the LCC, PFT-specific V cmax , and field measurements of V cmax for these sites (Figure 12a-i). ...
... Because a limited quantity of field-measured V cmax data are available for validation, remote sensing V cmax products have not yet been fully tested. Although efforts have been made to predict V cmax on the global scale using remote sensing data [55,57,58,131,143], the mechanisms driving the spatiotemporal variability in plant photosynthetic production (e.g., environmental acclimation, leaf age effect) are still ongoing [53,54,139]. ...
The value of leaf photosynthetic capacity (Vcmax) varies with time and space, but state-of-the-art terrestrial biosphere models rarely include such Vcmax variability, hindering the accuracy of carbon cycle estimations on a large scale. In particular, while the European terrestrial ecosystem is particularly sensitive to climate change, current estimates of gross primary production (GPP) in Europe are subject to significant uncertainties (2.5 to 8.7 Pg C yr−1). This study applied a process-based Farquhar GPP model (FGM) to improve GPP estimation by introducing a spatially and temporally explicit Vcmax derived from the satellite-based leaf chlorophyll content (LCC) on two scales: across multiple eddy covariance tower sites and on the regional scale. Across the 19 EuroFLUX sites selected for independent model validation based on 9 plant functional types (PFTs), relative to the biome-specific Vcmax, the inclusion of the LCC-derived Vcmax improved the model estimates of GPP, with the coefficient of determination (R2) increased by 23% and the root mean square error (RMSE) decreased by 25%. Vcmax values are typically parameterized with PFT-specific Vcmax calibrated from flux tower observations or empirical Vcmax based on the TRY database (which includes 723 data points derived from Vcmax field measurements). On the regional scale, compared with GPP, using the LCC-derived Vcmax, the conventional method of fixing Vcmax using the calibrated Vcmax or TRY-based Vcmax overestimated the annual GPP of Europe by 0.5 to 2.9 Pg C yr−1 or 5 to 31% and overestimated the interannually increasing GPP trend by 0.007 to 0.01 Pg C yr−2 or 14 to 20%, respectively. The spatial pattern and interannual change trend of the European GPP estimated by the improved FGM showed general consistency with the existing studies, while our estimates indicated that the European terrestrial ecosystem (including part of Russia) had higher carbon assimilation potential (9.4 Pg C yr−1). Our study highlighted the urgent need to develop spatially and temporally consistent Vcmax products with a high accuracy so as to reduce uncertainties in global carbon modeling and improve our understanding of how terrestrial ecosystems respond to climate change.
... Using the LMA data, we examined the relationships between leaf anatomical properties and LMA, LD, or LT for the 18 species. We tested the following three hypotheses: (1) plants on SFS have higher LTs with thicker palisade mesophyll than those on other slopes because thick palisade mesophyll may contribute to efficient photosynthesis under strong solar irradiation (Lambers et al., 2008;Niinemets et al., 2005); (2) plants on SFS have higher LDs than those on other slopes because of higher fractions of palisade mesophyll layers with less intercellular airspaces and higher tissue density than epidermis layers (Poorter et al., 2019); and (3) plants on SFS have higher LMAs than other slope aspects as the result of higher LTs and LDs. ...
... Our first hypothesis was in part supported by our results that the dominant species on the SFS exhibited slightly thicker PTs than those on other slopes. Thick PT on SFS may contribute to efficient photosynthesis under strong solar irradiation (Lambers et al., 2008;Niinemets et al., 2005). The dominant species on SFS also exhibited higher ST and its relative fraction than on NFS. ...
Abstract Leaf anatomy varies with abiotic factors and is an important trait for understanding plant adaptive responses to environmental conditions. Leaf mass per area (LMA) is a key morphological trait and is related to leaf performance, such as light‐saturated photosynthetic rate per leaf mass, leaf mechanical strength, and leaf lifespan. LMA is the multiplicative product of leaf thickness (LT) and leaf density (LD), both of which vary with leaf anatomy. Nevertheless, how LMA, LT, and LD covary with leaf anatomy is largely unexplored along natural environmental gradients. Slope aspect is a topographic factor that underlies variations in solar irradiation, air temperature, humidity, and soil fertility. In the present study, we examined (1) how leaf anatomy varies with different slope aspects and (2) how leaf anatomy is related to LMA, LD, and LT. Leaf anatomy was measured for 30 herbaceous species across three slope aspects (south‐, west‐, and north‐facing slopes; hereafter, SFS, WFS, and NFS, respectively) in an eastern Tibetan subalpine meadow. For 18 of the 30 species, LMA data were available from previous studies. LD was calculated as LMA divided by LT. Among the slope aspects, the dominant species on the SFS exhibited the highest LTs with the thickest spongy mesophyll layers. The thicker spongy mesophyll layer was related to a lower LD via larger intercellular airspaces. In contrast, LD was the highest on NFS among the slope aspects. LMA was not significantly different among the slope aspects because higher LTs on SFS were effectively offset by lower LDs. These results suggest that the relationships between leaf anatomy and LMA were different among the slope aspects. Mechanisms underlying the variations in leaf anatomy may include different solar radiation, air temperatures, soil water, and nutrient availabilities among the slope aspects.
... In addition to the changes that occur in photosynthetic responses based on several environmental factors, photosynthetic activities are also strongly limited by leaf ontogeny [9], leaf age [10] or other leaf structural traits [11]. Photosynthetic behaviors as a function of leaf age are usually related to the leaf nitrogen distribution [12][13], particularly resulting from acclimation to seasonal variability and leaf structural traits [14]. ...
... In addition, it has previously been found that an increasing demand for CO2 is associated with a higher gm response, leading to an increased CO2 concentration in chloroplasts [39]. Therefore, gm can be directly affected by the number of chloroplasts, which varies with structural traits in leaves of different ages [11]. The results of this study imply that vine leaves in the mature stage, or at 8 to 16 weeks of age, possess a greater potential ability to fix carbon than both young and senescing leaves. ...
Leaf aging induces various photosynthetic responses through changes in the growth and development of vines. This study aimed to estimate the responses of leaf photosynthetic capacity and leaf nitrogen content (N) investments throughout the growing season. The altered ambient light intensity and CO2 concentrations were demonstrated to affect the leaf photosynthetic capacity in grapevines at three different years of age based on non-rectangular hyperbola and A/Ci model approaches. The leaf growth stages were significantly higher for all leaf photosynthetic parameters than for the vine age factor, as estimated from the two main model approaches. In addition, the acclimation of the light-saturated photosynthetic rate (Pmax), maximum carbon assimilation rate (Amax) , apparent maximum rate of carboxylation due to Rubisco activity (Vc,max) and apparent maximum rate of electron transport in RuBP regeneration (Jmax) showed slight differences among vine ages, which gradually increased starting at 4 weeks and suddenly declined during the senescence stage, at 20 weeks after leaf unfolding. Similarly, the leaf N investments in terms of the photosynthetic nitrogen use efficiency (PNUE), Rubisco (Pr), bioenergetics (Pb) and thylakoid light harvesting (Pl) were slightly higher in the 18-year-old vines than the other vines. There was a stronger relationship between N investments and Vc,max than Jmax when the data for all leaf growth stages and vine ages were pooled. These findings suggest that this variation may lead to differences in the potential to predict photosynthetic carbon gains among leaves and vines of different ages.
... Leaf N content, carboxylation capacity and photosynthetic rate are age-dependent, as all are rather low shortly after emergence, increase as leaves expand until full expansion, but decrease progressively afterward as leaf senescence approaches (Kitajima et al. 2002, Ethier et al. 2006, Menezes et al. 2022. Age-dependent decreases in stomatal conductance and decreasing stomatal conductance sensitivity to ambient vapor pressure deficit (VPD) have been also widely observed in senescent leaves of broadleaf species (Reich and Borchert 1988, Niinemets et al. 2005, Ethier et al. 2006). On the other hand, leaf thickness and density generally increase as leaves age as a result of the phenological and ontogenic effects on carbon accumulation during leaf structural differentiation and development (Reich et al. 1991b, Chavana-Bryant et al. 2019. ...
N 2 ‐fixing legumes can strongly affect ecosystem functions by supplying nitrogen (N) and improving the carbon‐fixing capacity of vegetation. Still, the question of how their leaf‐level N status and carbon metabolism are coordinated along leaf ageing remains unexplored. Leaf tissue carbon isotopic composition (δ ¹³ C) provides a useful indicator of time‐integrated intrinsic water use efficiency (WUEi). Here, we quantified the seasonal changes of leaf δ ¹³ C, N content on a mass and area basis (N mass , N area , respectively), Δ ¹⁸ O (leaf ¹⁸ O enrichment above source water, a proxy of time‐integrated stomatal conductance) and morphological traits in an emblematic N 2 ‐fixing legume tree, the black locust ( Robinia pseudoacacia L.), at a subtropical site in Southwest China. We also measured xylem, soil and rainwater isotopes (δ ¹⁸ O, δ ² H) to characterize tree water uptake patterns. Xylem water isotopic data reveal that black locust primarily used shallow soil water in this humid habitat. Black locust exhibited a decreasing δ ¹³ C along leaf ageing, which was largely driven by decreasing leaf N mass , despite roughly constant N area . In contrast, the decreasing δ ¹³ C along leaf ageing was largely uncoupled from parallel increases in Δ ¹⁸ O and leaf thickness. Leaf N content is used as a proxy of leaf photosynthetic capacity; thus, it plays a key role in determining the seasonality in δ ¹³ C, whereas the roles of stomatal conductance and leaf morphology are minor. Black locust leaves can effectively adjust to changing environmental conditions along leaf ageing through LMA increases and moderate stomatal conductance reduction while maintaining constant N area to optimize photosynthesis and carbon assimilation, despite declining leaf N mass and δ ¹³ C.
... For future research, we suggest conducting comparative tests on branches that can be used for in-situ measurement. Previous work has also shown that compared to observation results collected in the field shortly after branch cutting (Niinemets et al., 2005), pre-treatment of cut branches under low light and constant temperature for 2-3 days may reduce bias related to cutting, which is not allowed to observe the gas exchange rate at the in-situ stress level. ...
Introduction
Canopy species need to shift their ecological adaptation to improve light and water resources utilization, and the study of intraspecific variations in plant leaf functional traits based at individual scale is of great significance for evaluating plant adaptability to climate change.
Methods
In this study, we evaluate how leaf functional traits of giant trees relate to spatial niche specialization along a vertical gradient. We sampled the tropical flagship species of Parashorea chinensis around 60 meters tall and divided their crowns into three vertical layers. Fourteen key leaf functional traits including leaf morphology, photosynthetic, hydraulic and chemical physiology were measured at each canopy layer to investigate the intraspecific variation of leaf traits and the interrelationships between different functional traits. Additionally, due to the potential impact of different measurement methods (in-situ and ex-situ branch) on photosynthetic physiological parameters, we also compared the effects of these two gas exchange measurements.
Results and discussion
In-situ measurements revealed that most leaf functional traits of individual-to-individual P. chinensis varied significantly at different canopy heights. Leaf hydraulic traits such as midday leaf water potential (MWP) and leaf osmotic potential (OP) were insignificantly correlated with leaf photosynthetic physiological traits such as maximal net assimilation rate per mass (A mass). In addition, great discrepancies were found between in-situ and ex-situ measurements of photosynthetic parameters. The ex-situ measurements caused a decrease by 53.63%, 27.86%, and 38.05% in A mass, and a decrease of 50.00%, 19.21%, and 27.90% in light saturation point compared to the in-situ measurements. These findings provided insights into our understanding of the response mechanisms of P. chinensis to micro-habitat in Xishuangbanna tropical seasonal rainforests and the fine scale adaption of different resultant of decoupled traits, which have implications for understanding ecological adaption strategies of P. chinensis under environmental changes.
... In the model, R d was found when PPFD was above the light compensation point of photosynthesis (50 μmol m − 2 s − 1 for date palm; Arab et al., 2016) and assumed to be 50% of R n (Niinemets et al., 2005;Watanabe et al., 2014). The R d at 25 • C (R d25 ) was obtained from the A n_leaf /C i curve analysis (see section 2.3). ...
... However, there may be a trade-off concerning carbon gain. Higher LMA which could indicate more packaged mesophyll cells inducing greater leaf internal resistance to CO 2 diffusion during drought (Niinemets et al. 2005), and lower leaf hydraulic e ciency could imply higher water stress inducing partial stomata closure (Brodribb et al. 2007). Our observations indicate that this applies to Pomegranate and Mandarin, which have the lowest g max ( Table 2) and high LMA. ...
The water relation strategy of a species (iso-anisohydric continuum as one of the most widely used definitions) is a key issue in the context of climate change. Given the difficulty of determining water relations strategy, there is a need for simple traits with a solid theoretical basis to estimate it. Among the many possibilities, traits associated with the "fast-slow" plant economics spectrum are particularly interesting. Avocado, Fig, Mandarin, Olive, Pomegranate, and Vine were characterized in terms of stomatal behavior, water potential at the turgor loss point (TLP), and Hydroscape Area, and the association of these metrics with leaf mass per area (LMA) and wood density (WDen) was explored. Our results showed high coordination between LMA and WDen across the six species, and both traits were related to metrics of water relation strategy. Species with less regulation of their water status tended to invest a greater amount of carbon per unit leaf area or unit stem volume with implications over hydraulic efficiency and water stress tolerance. WDen and TLP were the most powerful traits in estimating the water relation strategy for six fruit species. These traits are easy to measure, time-cost efficient, and appear central to coordinating multiple traits and behaviors along the water relations strategies. It is important to improve the understanding of these traits and their intraspecific variability to advance the understanding of how species and cultivars will respond to future scenarios and to design better selection, breeding, and agronomic strategies for climate change adapted agriculture.
... The value of Γ* from Bernacchi et al. (2002) was used for estimating gm from the variable J method. Rd is day respiration and was assumed to be 0.5 times the measured dark respiration (Rd = RD/2) (Piel et al. 2002, Niinemets et al. 2005. ...
... where I * denotes the CO 2 compensation point in the absence of mitochondrial respiration, calculated as 44.04 mol mol −1 following ref. (Bernacchi et al., 2002) and R d represents non-photorespiratory respiration in light, calculated as one half of R n (Niinemets et al., 2005). ...
Background : Phosphorus has been proposed as an important factor determining photosynthesis through improvements in leaf anatomical traits and carboxylation efficiency. However, little is known about the combined effects of straw mulch and P fertilizer on the relationship between flag leaf P content and photosynthesis.
Aims : This study conducted to determine the combined effects of straw mulch combined with P fertilizer on wheat flag leaf photosynthetic capacity and grain yield.
Methods : We performed field experiments during 2020–2022 to investigate the combined effects of straw mulch (0 and 8000 kg ha ⁻¹ ) with P fertilizer (0, 75, and 120 kg P 2 O 5 ha ⁻¹ ) in southwest China.
Results : Straw mulch with 75 kg P 2 O 5 ha ⁻¹ gave an 18.3% yield advantage over no mulch with 120 kg P 2 O 5 ha ⁻¹ . Straw mulching with P fertilizer increased flag leaf P content and increased stomatal density. These changes increased stomatal conductance, mesophyll conductance and net photosynthetic rate by 17.4%, 16.3%, and 20.8%, respectively, compared with no‐mulch plots. The increased P n was found associated with decreased stomatal and mesophyll limitation. Straw mulching with P fertilizer increased the activities of ribulose‐1,5‐bisphosphate carboxylase‐oxygenase and sucrose synthesis enzymes, thus promoting sucrose synthesis in flag leaves, which is beneficial for increasing grain number per m ² and grain yield.
Conclusions : Straw mulching combined with 75 kg P 2 O 5 ha ⁻¹ increased flag leaves P content and stomatal density, and increased stomatal and mesophyll conductance, resulting in improved leaf photosynthesis and grain yield.
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... where Г* is the non-photorespiratory CO 2 compensation point and R L is the day respiration. The Г* was taken from Bernacchi et al. (2002), as suggested by Flexas et al. (2009) for grapevine, and R L was derived from measurements of dark respiration (R d ) such as R L = R d /2 (Niinemets et al., 2005). Briefly, R d was determined by additional gas exchange measurement where six leaves from each treatment were used. ...
Studying new alternatives for promoting plant growth is crucial to face a changing climate. This study aimed to determine the beneficial effect of fungal strains isolated from the rhizospheric soil of two native plants from the Atacama Desert on physiological leaf traits of inoculated ‘Chardonnay’ grapevines. Rhizosphere fungi were isolated from Baccharis scandens and Solanum chilense and tested in vitro for plant growth-promoting traits, including indole acetic acid, phosphate solubilization, siderophore production, and polyamine production. Aspergillus niger, Microdochium bolleyi, and Westerdikeya centenaria were isolated, showing plant growth-promoting attributes and high salt tolerance in almost all tested isolates. Then, the fungi were stabilized and co-inoculated in pot-grown ‘Chardonnay’ plants (Vitis vinifera L.) growing in outdoor conditions to evaluate gas exchange variables, chlorophylls (as SPAD value), water potential, proline and sugar content, and lipid peroxidation in leaves. Inoculation of the fungal strains significantly increased the photosynthesis rate, which was associated with higher mesophyll conductance and SPAD values. The co-inoculation also induced an enhanced protective condition for oxidative damage. Increased carbon assimilation resulted in higher soluble sugars and intrinsic water use efficiency in leaves without altering the water status of treated plants. Our results demonstrated the beneficial effects of co-inoculating rhizosphere-inhabiting fungi isolated from native plants from the Atacama Desert on physiological traits of ‘Chardonnay’ grapevines.
... where Г* is the non-photorespiratory CO 2 compensation point and R L is the day respiration. The Г* was taken from Bernacchi et al. (2002), as suggested by Flexas et al. (2009) for grapevine, and R L was derived from measurements of dark respiration (R d ) such as R L = R d /2 (Niinemets et al., 2005). Briefly, R d was determined by additional gas exchange measurement where six leaves from each treatment were used. ...
... As expected, young plants had the highest isoprene emission rate because the biosynthesis of isoprene is based on a photosynthetically fixed carbon (Niinemets et al., 2002;Jardine et al., 2014;de Souza et al., 2018). Young culms had the highest photosynthetic rate and isoprene emission, which may be also related to the younger leaf age and different morphology (Niinemets et al., 2005). Notably, the isoprene emission rate of old plants was higher than that of mature plants; however, the opposite trend was observed for Pn. ...
Isoprene is a highly reactive volatile organic compound that significantly affects atmospheric oxidant capacity, regional air quality, and climate change. Moso bamboo (Phyllostachys edulis), a species widely distributed in tropical and subtropical regions, particularly in China, is a strong isoprene emitter with great potential for carbon sequestration. Carbon sequestration is negatively correlated with culm age; however, the effect of this correlation on isoprene emissions remains unknown. In this study, we investigated the photosynthetic and isoprene emission characteristics of Moso bamboo at different culm ages. The results showed that the age effect on isoprene emission was different from that on photosynthesis; the net photosynthesis rate (Pn) was the highest in young, followed by mature, and then old bamboo, whereas the isoprene emission rate (Iso) was the highest in young, followed by old, and then mature bamboo. Moreover, the percentage of carbon loss as isoprene emission (C-loss) during photosynthesis of old bamboo was 35% higher than that of mature bamboo under standard conditions (leaf temperature: 30°C; light intensity: 1000 µmol m-2 s-1). Therefore, we strongly recommend considering the culm age when establishing an isoprene emission model of Moso bamboo. Additionally, because the Iso and C-loss of old bamboo were higher than those of mature bamboo, we suggest that attention should be paid to the management of bamboo age structure and timely felling of aged bamboo to reduce environmental risk.
... In addition, as the leaves mature, the surface area of the cell wall and the thickness of the mesophyll cells increase, which increases the contact area with the chloroplasts, creating a larger space for chloroplast accumulation (Oguchi et al. 2003). This reduces the resistance of CO 2 diffusion in the cytoplasm and increases the utilization rate of CO 2 in plants (Niinemets et al. 2005, Terashima et al. 2011, Tholen et al. 2012. Marchi et al. (2008) also believed that the difference in photosynthetic potential from young leaves to mature leaves is related to the formation of mesophyll cells because the increase of mesophyll cells is often accompanied by a large increase in chlorophyll and Rubisco content. ...
Many studies have investigated the photoprotective and photosynthetic capacity of plant leaves but few have simultaneously evaluated the dynamic changes of photoprotective capacity and photosynthetic maturation of leaves at different developmental stages. This leads to the fact that the process between the decline of photoprotective substances and the onset of photosynthetic maturation during plant leaf development are still poorly understood, and the relationship between them has not been quantitatively described. In this study, the contents of photoprotective substances, photosynthetic pigment content and photosynthetic capacity of leaves at different developmental from young leaves to mature leaves, were determined by spatio-temporal replacement in 8 dominant tree species in subtropical evergreen broadleaved forests. The correlation analysis found that the data sets of anthocyanins, flavonoids, total phenolics, and total antioxidant capacity (TAC) were mainly distributed on one side of the symmetry axis (y = x), while the data sets of flavonoids, total phenolics and TAC were mainly distributed on both sides of the symmetry axis (y = x). In addition, the content of photoprotective substances in plant leaves was significantly negatively correlated with photosynthetic pigment content and photosynthetic capacity but was significantly positively correlated with dark respiration rate (Rd). When chlorophyll accumulated to approximately 50% of the final value, the photoprotective substance content and Rd of plant leaves reached the lowest level, and anthocyanins disappeared completely; in contrast, the photosynthetic capacity reached the highest level. Our results suggest that anthocyanins mainly play a light-shielding role in the young leaves of most plants in subtropical forests. In addition, 50% chlorophyll accumulation in most plant leaves was the basis for judging leaf photosynthetic maturity. We also believe that 50% chlorophyll accumulation is a critical period in the transition of plant leaves from high photoprotective capacity (high metabolic capacity, low photosynthetic capacity) to low photoprotective capacity (low metabolic capacity, high photosynthetic capacity).
... Therefore, a typical S c/o value of 97.5 mol mol −1 at 25°C was selected for all the species in the present study. R d is the daytime respiration rate, which was assumed to be half of the dark respiration rate (Niinemets et al., 2005). The dark respiration measurements were conducted in dark-adapted leaves using an LI-6400XT system equipped with a 6400-02B leaf chamber. ...
Increasing the mesophyll conductance to CO2 (gm ) is considered a strategy to improve photosynthesis in C3 crops. However, the relative importance of different anatomical traits in determining gm in crops is unclear. Mesophyll conductance measurements were performed on ten crops using the online carbon isotope discrimination method and the 'variable J' method in parallel. The influences of crucial leaf anatomical traits on gm were then evaluated using a one-dimensional anatomical CO2 diffusion model. The gm values measured using two independent methods were compatible, although significant differences were observed in their absolute values. Quantitative analysis showed that the cell wall thickness and chloroplast stroma thickness are the most important elements along the diffusion pathway. Unexpectedly, the large variability of gm across crops was not associated with any investigated leaf anatomical traits except chloroplast thickness. The anatomical model estimated gm values differed remarkably from the values measured in vivo in most species. However, when the species-specific effective porosity of the cell wall and the species-specific facilitation effect of CO2 diffusion across membrane and chloroplast stoma are taken into account, the model can output gm values very similar to those measured in vivo. These results indicate that gm variation across crops is probably also driven by cell wall effective porosity and effects of facilitation of CO2 transport across membrane and chloroplast stroma in addition to the thicknesses of the elements.
... We observed that with no soil moisture limitations (control conditions), on average, compound leaf species had greater photosynthetic capacity than simple leaf species, where the compound leaf tree species Prosopis chilensis and Acacia caven were the species showing the highest A N values. In P. chilensis, this could be due to the high values of g m (0.29 mol CO 2 m −2 s −1 on average, Table S1) that are on the range of values typically found on herbs (Tomás Nadal et al. 2018), and greater than the g m values reported for other Mediterranean species that typically ranged between 0.18 and 0.08 mol CO 2 m −2 s −1 (Niinemets et al. 2005(Niinemets et al. , 2009bGalmés et al. 2007;Peguero-Pina et al. 2012Tomás et al. 2013;Flexas et al. 2014;Alonso-Forn et al. 2020). ...
Two main leaf types are recognized among vascular plant species: compound and simple. Compound leaves are believed to be photosynthetically more productive than simple ones, by diluting mass tissue in more projected area. Conversely, simple leaves are believed to be more stress-tolerant by packing mass tissue in less projected area during stress like drought. Nevertheless, convective cooling is more efficient in compound than simple leaves, a process that could alleviate water loss in drought periods. In Central Chile, woody species with simple and compound leaves coexist. This zone is facing a mega-drought event, causing browning and tree mortality. However, how severe droughts affect photosynthetic traits on both leaf-type species have not been addressed so far. We measured photosynthetic traits in well-watered and drought conditions in three compound and three simple leaf species, and drought response ratios were obtained. We hypothesized that with no water limitation compound leaf species will show higher net photosynthesis (AN) than simple leaf species associated with a higher mesophyll conductance (gm). Opposite results are expected for simple leaf species due to their stress-tolerant physiology, showing fewer changes in their photosynthetic traits. We found that gm and AN were larger in compound leaf species in well-watered conditions. With drought, both leaf-type species were negatively affected despite foliar temperature in compound leaf species was 4 °C lower. Our result suggests that regardless of leaf shape the matorral species in Central Chile will be seriously affected in their AN due to the megadrought currently affecting this zone.
... In addition, leaf morphology and anatomy are key aspects in the physiological potential of adaptation of plants to environmental changes (Smith and McLean, 1989;Hanba et al., 2002). In general, evergreen species have more robust leaf structures than deciduous species, such as thicker cell walls and epidermis, greater mesophilic volume and leaf density (Castro-Díez et al., 2000;Niinemets et al., 2005;Enrique et al., 2016). Besides, leaf morpho-anatomical characteristics show a high responsiveness to environmental factors such as temperature, lighting, soil water availability or atmospheric CO 2 . ...
Increasing CO2 air concentration may affect wettability, anatomy and ultra-structure of leaves of Patagonian forest species, evergreen and deciduous plants potentially responding differently to such CO2 increases. In this study, we analysed the wettability, anatomy and ultra-structure of leaves of Nothofagus antarctica (deciduous) and N. betuloides (evergreen) grown under high CO2 concentrations. Leaf wettability was affected by increasing CO2, in different directions depending on species and leaf side. In both species, soluble cuticular lipid concentrations per unit leaf area raised with higher CO2 levels. Stomatal parameters (density, size of guard cells and pores) showed different responses to CO2 increasing depending on the species examined. In both species, leaf tissues showed a general trend to diminish with higher CO2 concentration. Cuticle thickness was modified with higher CO2 concentration in N. betuloides, but not in N. antarctica leaves. In both species, chloroplasts were often damaged with the increase in CO2 concentration. Our results show that several surface and internal leaf parameters can be modified in association with an increase in atmospheric CO2 concentration which may very among plant species.
... On the other hand, tougher leaves have increased internal resistance to CO 2 diffusion, which limits photosynthesis, i.e., increased toughness due to thick cell walls may lower the photosynthesis rate (Hikosaka, 2004;Niinemets et al., 2005;Morison et al., 2007;Niinemets, 2007;Terashima et al., 2011). In heterobaric species, leaf toughness had a strong positive correlation with photosynthesis, whereas for homobaric species the correlation was weaker. ...
Although leaf toughness is an essential plant adaptation to herbivore pressure and environmental stress, the relationships of leaf toughness with leaf anatomy and photosynthetic traits, and its spatial variations within tropical rainforests, remain poorly understood. We measured these traits in 103 tree species belonging to 27 families from the canopy to understory using a canopy crane system in a tropical rainforest in Sarawak, Malaysia. We focused on the leaf anatomical trait of bundle-sheath extensions (BSEs) around the vascular bundle due to their diverse ecophysiological functions. We divided the trees into heterobaric species with BSEs and homobaric species lacking BSEs, to investigate the relationships of leaf toughness with tree height, leaf functional traits such as carbon (C) and nitrogen (N) content, thickness, leaf mass per area (LMA) and the maximum photosynthetic rate ( P max ). Leaf toughness, LMA, thickness and C and N contents increased with height regardless of BSE presence. Heterobaric leaves had greater toughness than homobaric leaves, whereas leaf thickness, LMA and C were similar between the two leaf types throughout the height gradient. We found that standardized toughness per thickness or C was greater in heterobaric species, as BSEs consist mainly of fibrous tissue. P max was higher for heterobaric than homobaric leaves in the upper canopy presumably due to the functions of BSEs, including water conductivity, but did not differ with plant type in the lower layers. In other words, heterobaric species efficiently exploit the advantages of tougher leaves and higher P max by having BSEs. The increased proportion of heterobaric species, with their tougher leaves and higher P max , in the upper canopy is consistent with adaptation to physically stressful conditions in the tropical rainforest canopy, including high herbivore pressure and strong light.
... The remaining parameters (block temperature, VPD, flow rate, and c a ) were kept as described above. The R light value was calculated at 21% O 2 as half the dark-adapted mitochondrial respiration after plants were exposed to darkness for 30 min (Niinemets et al., 2005). Based on these parameters, g m was estimated by the variable J method (Harley et al., 1992) using the value for the CO 2 compensation point in the absence of respiration (Γ*) reported for tomato by Hermida-Carrera et al. (2016). ...
Water shortage strongly affects plants’ physiological performance. Since tomato (Solanum lycopersicum) non‐long shelf‐life (nLSL) and long shelf‐life (LSL) genotypes differently face water deprivation, we subjected a nLSL and a LSL genotype to four treatments: control (well‐watering), short‐term water deficit stress at 40% field capacity (ST 40% FC), short‐term water deficit stress at 30% FC (ST 30% FC) and short‐term water deficit stress at 30% FC followed by recovery (ST 30% FC‐Rec). Treatments’ imposition promoted genotypic‐dependent elastic adjustments accompanied by distinct photosynthetic responses. Whilst the nLSL genotype largely modified mesophyll conductance (gm) across treatments, it was kept within a narrow range in the LSL. However, similar gm values were achieved under ST 30% FC. Particularly, modifications in the relative abundance between cell wall compounds and in sub‐cellular anatomic parameters such as the chloroplasts surface area exposed to intercellular air spaces per leaf area (Sc/S) and the cell wall thickness (Tcw), regulated gm in the LSL genotype. Instead, only changes in foliar structure at supra‐cellular level influenced gm in the nLSL. Even though further experiments testing a larger range of genotypes and treatments would be valuable to reinforce these statements, we show for the first time that even genotypes of the same species can present different elastic, anatomical and cell wall composition mediated‐mechanisms to regulate gm when subjected to distinct water regimes.
... Previous studies of leaf functional traits also extrapolated that phenotypic plasticity was the dominant source of within-species trait variability in Eucalyptus camaldulensis and Quercus ilex (Valladares et al., 2002;Niinemets, 2015;Asao et al., 2020), although genotypic variation explained significant variation in leaf functional traits in nine switchgrass genotypes (Aspinwall et al., 2013). Differences in plant/leaf age and sampling time can be another source of within-species trait variation in multiple species or the Glopnet database (Niinemets et al., 2005;Mason et al., 2013;McKown et al., 2013;Niinemets, 2015). In our study, all genotypes were planted on the same date and all leaves used for the measurements had similar age at each site and in each year, minimizing the effect of plant/leaf age on leaf traits. ...
The leaf economics spectrum (LES) describes multivariate correlations in leaf structural, physiological and chemical traits, originally based on diverse C3 species grown under natural ecosystems. However, the specific contribution of C4 species to the global LES is studied less widely. C4 species have a CO2 concentrating mechanism which drives high rates of photosynthesis and improves resource use efficiency, thus potentially pushing them towards the edge of the LES. Here, we measured foliage morphology, structure, photosynthesis, and nutrient content for hundreds of genotypes of the C4 grass Miscanthus × giganteus grown in two common gardens over two seasons. We show substantial trait variations across M. × giganteus genotypes and robust genotypic trait relationships. Compared to the global LES, M. × giganteus genotypes had higher photosynthetic rates, lower stomatal conductance, and less nitrogen content, indicating greater water and photosynthetic nitrogen use efficiency in the C4 species. Additionally, tetraploid genotypes produced thicker leaves with greater leaf mass per area and lower leaf density than triploid genotypes. By expanding the LES relationships across C3 species to include C4 crops, these findings highlight that M. × giganteus occupies the boundary of the global LES and suggest the potential for ploidy to alter LES traits. This article is protected by copyright. All rights reserved.
... Meanwhile, the decreasing ability of phloem to export photosynthates with needle age, which has been observed in previous studies of evergreen conifers (Egger et al., 1996;Li et al., 2009). Moreover, older needles act as storage organs which tend to store more NSC to support the growth or new leaf development (Niinemets et al., 2005;Yan et al., 2022). These results indicated that the effect of needle age on N fractions differed from C fractions in a Chinese fir plantation. ...
Forest productivity is generally limited by nutrient scarcity. This study aims to reveal seasonal interactions among leaf carbon (C), nitrogen (N) fractions and tree growth driven by nutrient addition in a subtropical forest. Here, a field nutrient addition experiment was conducted with six treatments, namely, +N5 (5 g N m⁻² yr⁻¹), +N10 (10 g N m⁻² yr⁻¹), +P5 (5 g P m⁻² yr⁻¹), +N5 + P5, +N10 + P5, and control (N0 + P0). C fractions (structural and non-structural carbohydrates) and N fractions (soluble N, nucleic N and protein N) in needles as well as tree growth indicated by basal area increment (BAI) were measured in growing and dormant seasons. Total N and protein N in old needles were significantly increased by P addition, while no significant differences of non-structural carbohydrates in young (<1-year old) and old needles (>1-year old) were detected among the treatments in both seasons. N and P addition increased the structural carbohydrates of old needles in dormant season. P addition decreased and increased tree growth in growing and dormant seasons, respectively. The variation of BAI was explained 18.3 % by total N and 17.8 % by protein N in growing season, and was explained 33.9 % by total N and 34.2 % by protein N in dormant season. Our study suggested that the P addition effect on Chinese fir growth mostly depends on needle N fractions. This study highlights tree seasonal growth driven by nutrient alteration might be characterized by leaf N fractions rather than C fractions in subtropical forests.
... where the day respiration rate (R d ) was assumed to be half of the dark respiration rate (Niinemets et al., 2005;Villar et al., 1995). The J F (photosynthetic electron transport rate) was calculated according to J F = Φ PSⅡ PPFDαβ with the leaf absorptance (α), the fraction of light absorbed by PSII (β), PPFD and Φ PSII . ...
Leaf growth relies on photosynthesis and hydraulics to provide carbohydrates and expansion power; in turn, leaves intercept light and construct organism systems for functioning. Under potassium (K) deficiency stress, leaf area, photosynthesis and hydraulics are all affected by alterations in leaf structure. However, the connection between changes in leaf growth and function caused by structure under K regulation is unclear. Consequently, the leaf hydraulic conductance (Kleaf) and photosynthetic rate (A) combined with leaf anatomical characteristics of Brassica napus were continuously observed during leaf growth under different K supply levels. The results showed that Kleaf and A decreased simultaneously after leaf area with the increasing K deficiency stress. K deficiency significantly increased longitudinal mesophyll cell investment, leading to reduced the volume fraction of intercellular air‐space (fias) and decreased leaf expansion rate. Furthermore, reduced fias decreased mesophyll and chloroplast surfaces exposed to intercellular airspace and gas phase H2O transport, which induced coordinated changes in CO2 mesophyll conductance and hydraulic conductance in extra‐xylem pathways. Adequate K supply facilitated higher fias through smaller palisade tissue cell density (loose mesophyll cell arrangement) and smaller spongy tissue cell size, which coordinated CO2 and H2O conductance and promoted leaf area expansion. This article is protected by copyright. All rights reserved.
... How sensitive g m and l m of bryophytes are to the method used for calculating them remains unexplored. Both the curvefitting and variable J methods have been correlated in tracheophytes, with g m derived from the variable J method (g mVJ ) either somewhat lower than that calculated from the curvefitting method (g mCF ) (Pons et al., 2009;Sade et al., 2014;Carriquí et al., 2015) or with not difference (Niinemets et al., 2005;Warren and Dreyer, 2006;Flexas et al., 2007;Peguero-Pina et al., 2012;Veromann-Jürgenson et al., 2017). Both the curvefitting (Perera-Castro and Flexas, 2022) and variable J methods Perera-Castro et al., 2020b) have also been used for calculating g m in bryophytes. ...
Bryophytes are the group of land plants with the lowest photosynthetic rates, which was considered to be a consequence of their higher anatomical CO2 diffusional limitation compared with tracheophytes. However, the most recent studies assessing limitations due to biochemistry and mesophyll conductance in bryophytes reveal discrepancies based on methodology used. In this study, we compared data calculated from two different methodologies for estimating mesophyll conductance: variable J and the curve-fitting method. Although correlated, mesophyll conductance estimated by the curve-fitting method was on average 4-fold higher than the conductance obtained by the variable J method; a large enough difference to account for the scale of differences previously shown between the biochemical and diffusional limitations to photosynthesis. Biochemical limitations were predominant when the curve-fitting method was used. We also demonstrated that variations in bryophyte relative water content during measurements can also introduce errors in the estimation of mesophyll conductance, especially for samples which are overly desiccated. Furthermore, total chlorophyll concentration and soluble proteins were significantly lower in bryophytes than in tracheophytes and the percentage of proteins quantified as rubisco was also significantly lower in bryophytes (less than 6.3% in all studied species) than in angiosperms (more than 16% in all non-stressed cases). Photosynthetic rates normalized by rubisco were not significantly different between bryophytes and angiosperms. Our data suggest that the biochemical limitation to photosynthesis in bryophytes is more relevant than so far assumed.
... Ambient CO 2 concentration was regulated at 400 µmol CO 2 mol −1 air, the photosynthetic photon flux density was set at a saturating flux of 1500 µmol m −2 s −1 and the temperature was maintained between 14°C and 21°C (target at 20°C) depending on the hour and day. The leaf mesophyll conductance to CO 2 (g m ) was calculated as in Limousin et al. (2010b) by using the variable electron transport rate method proposed by Harley et al. (1992), the specific coefficients for holm oak proposed by Niinemets et al. (2005) for the relationship between the photosynthetic electron transport rate and the efficiency of the photosystem II, and the temperature correction coefficients proposed by Bernacchi et al. (2002). ...
Increasing temperature and drought can result in leaf dehydration and defoliation even in drought‐adapted tree species such as the Mediterranean evergreen Quercus ilex L. The stomatal regulation of leaf water potential plays a central role in avoiding this phenomenon and is constrained by a suite of leaf traits including hydraulic conductance and vulnerability, hydraulic capacitance, minimum conductance to water vapor, osmotic potential and cell wall elasticity. We investigated whether the plasticity in these traits may improve leaf tolerance to drought in two long‐term rainfall exclusion experiments in Mediterranean forests. Osmotic adjustment was observed to lower the water potential at turgor loss in the rainfall‐exclusion treatments, thus suggesting a stomatal closure at more negative water potentials and a more anisohydric behavior in drier conditions. Conversely, leaf hydraulic conductance and vulnerability did not exhibit any plasticity between treatments so the hydraulic safety margins were narrower in the rainfall‐exclusion treatments. The sequence of leaf responses to seasonal drought and dehydration was conserved among treatments and sites but trees were more likely to suffer losses of turgor and hydraulic functioning in the rainfall‐exclusion treatments. We conclude that leaf plasticity might help the trees to tolerate moderate drought but not to resist severe water stress. This article is protected by copyright. All rights reserved.
... where A N is the net photosynthetic rate, C i is the intercellular CO 2 concentration, R d is the non-photorespiratory respiration in light, and Γ* (44.04 μmol mol −1 ) is the CO 2 compensation point in the absence of mitochondrial respiration (computed according to Bernacchi et al. (2002) at 30 °C. R d was estimated as half the dark respiration rate (R n ; Niinemets et al., 2005). R n was measured by the Li-6400 after plants had been dark-adapted for more than half an hour in the evening. ...
Mesophyll conductance (gm) is a crucial leaf trait contributing to the photosynthetic rate (AN). Plant domestication typically leads to an enhancement of AN that is often associated with profound anatomical modifications, but it is unclear which of these structural alterations influence gm. We analyzed the implication of domestication on leaf anatomy and its effect on gm in 26 wild and 31 domesticated cotton genotypes (Gossypium sp.) grown under field conditions. We found that domesticated genotypes had higher AN but similar gm to wild genotypes. Consistent with this, domestication did not translate into significant differences in the fraction of mesophyll occupied by intercellular air spaces (fias) or mesophyll and chloroplast surface area exposed to intercellular air space (Sm/S and Sc/S, respectively). However, leaves of domesticated genotypes were significantly thicker, with larger but fewer mesophyll cells with thinner cell
walls. Moreover, domesticated genotypes had higher cell wall conductance (gcw) but smaller cytoplasmic conductance (gcyt) than wild genotypes. It appears that domestication in cotton has not generally led to significant improvement in gm, in part because their thinner mesophyll cell walls (increasing gcw) compensate for their lower gcyt, itself due to larger distance between plasmalemma and chloroplast envelopes
... These leaf morphological changes may help to increase the tolerance against hydraulic dysfunction in plants subjected to water deficit conditions (Sancho-Knapik et al., 2021). However, the increase of LMA may be associated with thicker leaves leading to a limitation of CO 2 diffusion in the gas phase due to a low sub-stomatal air space and/or liquid phase due to increased cell density and thick cell walls (Fini et al., 2016;Niinemets et al., 2005;Peguero-Pina et al., 2017). In addition, a recent study suggests that the increase in LMA may be related to a change in the cell wall composition upon abiotic stresses, which may affect the variation of g mCO2 . ...
Mesophyll conductance (gmCO2) is one of the most important components in plant photosynthesis. Tropospheric ozone (O3) and drought impair physiological processes, causing damage to photosynthetic systems. However, the combined effects of O3 and drought on gmCO2 are still largely unclear. We investigated leaf gas exchange during mid‐summer in three Mediterranean oaks exposed to O3 (ambient [35.2 nmol mol−1 as daily mean]; 1.4 × ambient) and water treatments (WW [well‐watered] and WD [water‐deficit]). We also examined if leaf traits (leaf mass per area [LMA], foliar abscisic acid concentration [ABA]) could influence the diffusion of CO2 inside a leaf. The combination of O3 and WD significantly decreased net photosynthetic rate (PN) regardless of the species. The reduction of photosynthesis was associated with a decrease in gmCO2 and stomatal conductance (gsCO2) in evergreen Q. ilex, while the two deciduous oaks (Q. pubescens, Q. robur) also showed a reduction of the maximum rate of carboxylation (Vcmax) and maximum electron transport rate (Jmax) with decreased diffusive conductance parameters. The reduction of gmCO2 was correlated with increased [ABA] in the three oaks, whereas there was a negative correlation between gmCO2 with LMA in Q. pubescens. Interestingly, two deciduous oaks showed a weak or no significant correlation between gsCO2 and ABA under high O3 and WD due to impaired stomatal physiological behaviour, indicating that the reduction of PN was related to gmCO2 rather than gsCO2. The results suggest that gmCO2 plays an important role in plant carbon gain under concurrent increases in the severity of drought and O3 pollution.
... The photosynthesis model of Farquhar et al. (1980) was fitted to the net assimilation vs. intercellular CO 2 (C i ) response curves [36], the maximum rate of carboxylation (V cmax ). The maximum rate of electron transport (J max ) was estimated as described in Niinemets et al. (2005) [37]. ...
Nitrogen (N) and/or phosphorus (P) addition has controversial effects on tree functional traits and growth; however, this experimental approach may clarify these controversial results. In this study, field and pot experiments were designed with +N (100 kg N ha−1 yr−1), +P (50 kg P ha−1 yr−1), +NP (100 kg N plus 50 kg P ha−1 yr−1), and a control (no N or P addition) to comparatively investigate the effects of N and P addition on 24 leaf traits and the growth rate of Schima superba (Reinw. ex Blume ) seedlings in subtropical China. We found that the experimental approach alters N and P addition effects on leaf traits and tree growth. Nitrogen addition strongly altered leaf biochemical and physiological traits and limited tree growth compared to P addition in the pot experiment, while the effects of N and P addition on leaf traits and tree growth were weaker in the field, since the seedlings might be mainly limited by light availability rather than nutrient supplies. The inference from the pot experiment might amplify the impact of N deposition on forest plants in complicated natural systems. These findings will help guide refining pot fertilization experiments to simulate trees in the field under environmental change. Future directions should consider reducing the confounding effects of biotic and abiotic factors on fertilization in the field, and refinement of the control seedlings’ genetic diversity, mycorrhizal symbiont, and root competition for long-term fertilization experiments are required.
... The photosynthesis model of Farquhar et al. (1980) was fitted to the net assimilation vs. intercellular CO 2 (C i ) response curves, the maximum rate of carboxylation (V cmax ). The maximum rate of electron transport (J max ) was estimated according to Niinemets et al. (2005). ...
Tree competitiveness generally depends on trait plasticity in response to environmental change. The effects of nitrogen (N) and phosphorus (P) on leaf trait variability by species is poorly understood, especially in China’s subtropical forests. This study examined the seedling leaf traits and net primary productivity of all trees ˃5 cm DBH of two dominant species, Schima superba and Castanopsis carlesii, in an evergreen broadleaved forest fertilized with nitrogen (+ N), phosphorus (+ P), and nitrogen plus phosphorus (N + P). The effect of N on seedling leaf traits was stronger than P, while fertilization in general was species dependent. Leaf mass per unit area decreased with N for S. superba seedlings but not for C. carlesii. Leaf N, P, and N/P ratios changed with N addition for both species. All four N fractions of carboxylation, bioenergetics, cell wall, and other N metabolites in C. carlesii leaves responded significantly to fertilization, while only the cell wall in S. superba leaves responded. Other leaf functional traits, including light-saturated photosynthetic rates, water, N, and P use efficiencies, chlorophyll and nonstructural carbohydrate contents increased with N addition in S. superba and by P addition in C. carlesii. Canopy closure at the stand-level increased due to N. Litter biomass and relative growth rate of S. superba was not affected by any treatments, while both for C. carlesii significantly decreased with N + P addition. Collectively, nutrient limitation may vary at a small scale among species in a subtropical forest based on their responses of seedling traits and net primary productivity to fertilization. Seedling traits are not correlated with the net primary productivity of larger trees except for N fractions, because low light conditions induced by fertilization reduces the proportion of N allocated to photosynthesis in seedlings. In addition, acclimation differences of tree species may increase the uncertainty of community succession.
... where C i represents intercellular CO 2 concentration (µmol CO 2 mol −1 ), R d represents the light mitochondrial respiration (µmol CO 2 m −2 s −1 ) and was calculated as 1/2 of the dark respiration (R n ) [33,63], R n was measured in the dark environment after the light was turned off for 3 h. Γ * is the chloroplast CO 2 compensation point in the absence of respiration (µmol CO 2 mol −1 ) and calculated according to [64] . ...
Background
Leaf hydraulic and economics traits are critical for balancing plant water and CO2 exchange, and their relationship has been widely studied. Leaf anatomical traits determine the efficiency of CO2 diffusion within mesophyll structure. However, it remains unclear whether leaf anatomical traits are associated with leaf hydraulic and economics traits acclimation to long-term drought.
Results
To address this knowledge gap, eight hydraulic traits, including stomatal and venation structures, four economics traits, including leaf dry mass per area (LMA) and the ratio between palisade and spongy mesophyll thickness (PT/ST), and four anatomical traits related to CO2 diffusion were measured in tomato seedlings under the long-term drought conditions. Redundancy analysis indicated that the long-term drought decreased stomatal conductance (gs) mainly due to a synchronized reduction in hydraulic structure such as leaf hydraulic conductance (Kleaf) and major vein width. Simultaneously, stomatal aperture on the adaxial surface and minor vein density (VDminor) also contributed a lot to this reduction. The decreases in mesophyll thickness (Tmes) and chlorophyll surface area exposed to leaf intercellular air spaces (Sc/S) were primarily responsible for the decline of mesophyll conductance (gm) thereby affecting photosynthesis. Drought increased leaf density (LD) thus limited CO2 diffusion. In addition, LMA may not be important in regulating gm in tomato under drought. Principal component analysis revealed that main anatomical traits such as Tmes and Sc/S were positively correlated to Kleaf, VDminor and leaf thickness (LT), while negatively associated with PT/ST.
Conclusions
These findings indicated that leaf anatomy plays an important role in maintaining the balance between water supply and CO2 diffusion responses to drought. There was a strong coordination between leaf hydraulic, anatomical, and economical traits in tomato seedlings acclimation to long-term drought.
... Variations in LMA could be driven by several anatomical traits, such as the cell wall thickness and number of mesophyll layers [34], and changes in LMA always influence g m [35]. If a lower LMA is the result of mesophyll cell wall thinning, it will increase g m [36,37]; if it is the result of a lower number of mesophyll layers, it will decrease g m [38]. In this study, the LMA of D. odorifera, C. hystrix, and B. alnoides decreased under the 10% irradiance treatment, indicating that low light may decrease the number of mesophyll layers in these tree seedlings. ...
Low light intensity can lead to a decrease in photosynthetic capacity. However, could N-fixing species with higher leaf N contents mitigate the effects of low light? Here, we exposed seedlings of Dalbergia odorifera and Erythrophleum fordii (N-fixing trees), and Castanopsis hystrix and Betula alnoides (non-N-fixing trees) to three irradiance treatments (100%, 40%, and 10% sunlight) to investigate the effects of low irradiance on leaf structure, leaf N allocation strategy, and photosynthetic physiological parameters in the seedlings. Low irradiance decreased the leaf mass per unit area, leaf N content per unit area (Narea), maximum carboxylation rate (Vcmax), maximum electron transport rate (Jmax), light compensation point, and light saturation point, and increased the N allocation proportion of light-harvesting components in all species. The studied tree seedlings changed their leaf structures, leaf N allocation strategy, and photosynthetic physiological parameters to adapt to low-light environments. N-fixing plants had a higher photosynthesis rate, Narea, Vcmax, and Jmax than non-N-fixing species under low irradiance and had a greater advantage in maintaining their photosynthetic rate under low-radiation conditions, such as under an understory canopy, in a forest gap, or when mixed with other species.
... -24,460/8.314/(273.15 + T L ))), where T L is the leaf temperature ( • C); R d is day respiration, assumed to be 0.5 times the measured dark respiration (R n ) (R d = R n /2, Piel et al. 2002, Niinemets et al. 2005. ...
The induction and relaxation of photochemistry and non-photochemical quenching (NPQ) are not instantaneous and require time to respond to fluctuating environments. There is a lack of integrated understanding on how photochemistry and NPQ influence photosynthesis in fluctuating environments. We measured the induction and relaxation of chlorophyll a fluorescence and gas exchange in poplar and cotton at varying temperatures under saturating and fluctuating lights. When the light shifted from dark to high, the fraction of open reaction centers in photosystem II (qL) gradually increased while NPQ increased suddenly and then remained stable. Temperature significantly changed the response of qL but not that of NPQ during the dark to high light transition. Increased qL led to higher photosynthesis but their precise relationship was affected by NPQ and temperature. qL was significantly related to biochemical capacity. Thus, qL appears to be a strong indicator of the activation of carboxylase, leading to the similar dynamics between qL and photosynthesis. When the light shifted from high to low intensity, NPQ is still engaged at a high level, causing a stronger decline in photosynthesis. Our finding suggests that the dynamic effects of photochemistry and NPQ on photosynthesis depend on the phases of environmental fluctuations and interactive effects of light and temperature. Across the full spectra of light fluctuation, the slow induction of qL is a more important limiting factor than the slow relaxation of NPQ for photosynthesis in typical ranges of temperature for photosynthesis. The findings provided a new perspective to improve photosynthetic productivity with molecular biology under natural fluctuating environments.
... Due to logistic restrictions to perform light curves under non-photorespiratory conditions (Valentini et al., 1995), for numerous mosses was used. The light respiration (R light ) was assumed to be half the dark respiration rate, measured after plants exposure to darkness for, at least, 30 min (Niinemets et al., 2005). ...
Cell wall thickness (Tcw) has been proposed as an important anatomical trait that could determine photosynthesis through land plants’ phylogeny, bryophytes being the plant group presenting the thickest walls and the lowest photosynthetic rates. Also, it has recently been suggested that cell wall composition may have the potential to influence both thickness and mesophyll conductance (gm), representing a novel trait that could ultimately affect photosynthesis. However, only a few studies in spermatophytes have demonstrated this issue. In order to explore the role of cell wall composition in determining both Tcw and gm in mosses, we tested six species grown under field conditions in Antarctica. We performed gas exchange and chlorophyll fluorescence measurements, an anatomical characterization, and a quantitative analysis of cell wall main composition (i.e., cellulose, hemicelluloses and pectins) in these six species. We found the photosynthetic rates to vary between the species, and they also presented differences in anatomical characteristics and in cell wall composition. Whilst gm correlated negatively with Tcw and pectins content, a positive relationship between Tcw and pectins emerged, suggesting that pectins could contribute to determine cell wall porosity. Although our results do not allow us to provide conclusive statements, we suggest for the first time that cell wall composition –with pectins playing a key role– could strongly influence Tcw and gm in Antarctic mosses, ultimately defining photosynthesis.
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... The electron transport rate (ETR) was calculated as described in Valentini et al. (1995) by the performance of light curves under negligible photorespiratory conditions (≃ 1% O 2 ). The dark respiration rate was estimated after plants acclimation to darkness for 30 min (Niinemets et al., 2005). The light mitochondrial non-photorespiratory respiration rate (R light ) was assumed to be half the dark respiration rate. ...
Based on a previous work, exposure to limited water availability induced changes in cell wall composition of mature Helianthus annuus L. leaves that affected mesophyll conductance to CO2 diffusion (gm). However, it is unclear on which timescale these cell wall composition changes occur. Here, we tested H. annuus subjected to control (i.e., water availability), different levels of short-term water deficit stress (ST), long-term water deficit stress (LT) and long-term water deficit stress followed by gradual recoveries addressed at different timescales (LT-Rec) to evaluate the dynamics of modifications in cell wall main composition (cellulose, hemicelluloses, pectins and lignins) affecting photosynthesis. During gradual ST treatments, pectins enhancements were associated with gm declines. However, during LT-Rec, pectins content decreased significantly after only 5 h, while hemicelluloses and lignins amounts changed after 24 h, all of them being uncoupled from gm. Surprisingly, lignins increased by around 200% as compared to control and were related to stomatal conductance to gas diffusion (gs) during LT-Rec. Although we suspect that the accuracy of the protocols to determine cell wall composition should be re-evaluated, we demonstrate for the first time that a highly dynamic cell wall composition turnover differently affects photosynthesis in plants subjected to distinct water regimes.
... Moreover, light curves under non-photorespiratory conditions (< 1% O 2 ) were performed to estimate the electron transport rate (ETR) following Valentini et al. [50]. Light respiration (R light ) was considered as half the dark-adapted respiration rate after plants exposition to darkness for, at least, 30 min [51]. As leaves did not cover the whole area of the IRGA cuvette, a picture of the leaf fraction enclosed in the cuvette was taken to recalculate the area with ImageJ. ...
In the current climate change scenario, understanding crops’ physiological performance under water shortage is crucial to overcome drought periods. Although the implication of leaf water relations maintaining leaf turgor and stomatal functioning under water deprivation has been suggested, the relationships between photosynthesis and osmotic and elastic adjustments remain misunderstood. Similarly, only few studies in dicotyledonous analysed how changes in cell wall composition affected photosynthesis and leaf water relations under drought. To induce modifications in photosynthesis, leaf water relations and cell wall composition, Hordeum vulgare and Triticum aestivum were subjected to different water regimes: control (CL, full irrigation), moderate and severe water deficit stress (Mod WS and Sev WS, respectively). Water shortage decreased photosynthesis mainly due to stomatal conductance (gs) declines, being accompanied by reduced osmotic potential at full turgor (πo) and increased bulk modulus of elasticity (ε). Whereas both species enhanced pectins when intensifying water deprivation, species-dependent adjustments occurred for cellulose and hemicelluloses. From these results, we showed that πo and ε influenced photosynthesis, particularly, gs. Furthermore, the (Cellulose+Hemicelluloses)/Pectins ratio determined ε and mesophyll conductance (gm) in grasses, presenting the lowest pectins content within angiosperms. Thus, we highlight the relevance of cell wall composition regulating grasses physiology during drought acclimation.
... Indeed, studies on the influence of leaf age on plant gas exchange offer promising insights. In general, photosynthesis and stomatal conductance decrease with leaf age mostly because the foliar nitrogen content is gradually reduced as the leaf is aging (Kositsup et al., 2010;Zhang et al., 2010) and also because mesophyll diffusion constraints photosynthesis more in older than in younger leaves (Niinemets et al., 2005). The influence of leaf age on photosynthesis does not depend on leaf longevity and instead relies on complex biochemical and structural dynamics (Mediavilla and Escudero, 2003;Pantin et al., 2012). ...
Herbivore insects have strong impacts on leaf gas exchange when feeding on the plant. Leaf age also drives leaf gas exchanges but the interaction of leaf age and phloem herbivory has been largely underexplored. We investigated the amplitude and direction of herbivore impact on leaf gas exchange across a wide range of leaf age in the apple tree–apple green aphid (Aphis pomi) system. We measured the gas exchange (assimilation and transpiration rates, stomatal conductance and internal CO2 concentration) of leaves infested versus non-infested by the aphid across leaf age. For very young leaves up to 15 days-old, the gas exchange rates of infested leaves were similar to those of non-infested leaves. After few days, photosynthesis, stomatal conductance and transpiration rate increased in infested leaves up to about the age of 30 days, and gradually decreased after that age. By contrast, gas exchanges in non-infested leaves gradually decreased across leaf age such that they were always lower than in infested leaves. Aphids were observed on relatively young leaves up to 25 days and despite the positive effect on leaf photosynthesis and leaf performance, their presence negatively affected the growth rate of apple seedlings. Indeed, aphids decreased leaf dry mass, leaf surface, and leaf carbon content except in old leaves. By contrast, aphids induced an increase in leaf nitrogen content and the deviation relative to non-infested leaves increased with leaf age. Overall, the impacts of aphids at multiple levels of plant performance depend on leaf age. While aphids cause an increase in some leaf traits (gas exchanges and nitrogen content), they also depress others (plant growth rate and carbon content). The balance between those effects, as modulated by leaf age, may be the key for herbivory mitigation in plants.
... Such C uptake reductions may still have severe implications for post-drought xylem and canopy recovery (e.g., Yan et al., 2017;Ruehr et al., 2019;Kannenberg et al., 2020). However, negative impacts of leaf losses are probably less severe because mostly the older leaves, which are less efficient in terms of photosynthesis, were shed first (Escudero and Mediavilla, 2003;Niinemets et al., 2005, but see Poyatos et al., 2013). Also, the C balance during drought is less negative because of reduced maintenance respiration; thus, lower depletion of non-structural carbohydrates reserves is expected. ...
During drought, trees reduce water loss and hydraulic failure by closing their stomata, which also limits photosynthesis. Under severe drought stress, other acclimation mechanisms are trigged to further reduce transpiration to prevent irreversible conductance loss. Here, we investigate two of them: the reversible impacts on the photosynthetic apparatus, lumped as non-stomatal limitations (NSL) of photosynthesis, and the irreversible effect of premature leaf shedding. We integrate NSL and leaf shedding with a state-of-the-art tree hydraulic simulation model (SOX+) and parameterize them with example field measurements to demonstrate the stress-mitigating impact of these processes. We measured xylem vulnerability, transpiration, and leaf litter fall dynamics in Pinus sylvestris (L.) saplings grown for 54 days under severe dry-down. The observations showed that, once transpiration stopped, the rate of leaf shedding strongly increased until about 30% of leaf area was lost on average. We trained the SOX+ model with the observations and simulated changes in root-to-canopy conductance with and without including NSL and leaf shedding. Accounting for NSL improved model representation of transpiration, while model projections about root-to-canopy conductance loss were reduced by an overall 6%. Together, NSL and observed leaf shedding reduced projected losses in conductance by about 13%. In summary, the results highlight the importance of other than purely stomatal conductance-driven adjustments of drought resistance in Scots pine. Accounting for acclimation responses to drought, such as morphological (leaf shedding) and physiological (NSL) adjustments, has the potential to improve tree hydraulic simulation models, particularly when applied in predicting drought-induced tree mortality.
... where A N is the net photosynthetic rate, C i is the intercellular CO 2 concentration, R d is the non-photorespiratory respiration in light, and Γ* (44.04 μmol mol −1 ) is the CO 2 compensation point in the absence of mitochondrial respiration (computed according to Bernacchi et al. (2002) at 30 °C. R d was estimated as half the dark respiration rate (R n ; Niinemets et al., 2005). R n was measured by the Li-6400 after plants had been dark-adapted for more than half an hour in the evening. ...
Mesophyll conductance (gm) is a crucial leaf trait contributing to photosynthetic rate (AN). Plant domestication typically leads to an enhancement of AN that is often associated with profoundly anatomical modifications but it is unclear which of these structural alterations influence gm. We analyzed the implication of domestication on leaf anatomy and its effect on gm in 26 wild and 31 domesticated cotton genotypes (Gossypium sp.) grown under field conditions. We found that domesticated genotypes had higher AN but similar gm to wild genotypes. Consistent with this, domestication did not translate into significant differences in the fraction of mesophyll occupied by intercellular airspaces (fias) or mesophyll and chloroplast surface area exposed to intercellular airspace (Sm/S and Sc/S, respectively). However, leaves of domesticated genotypes were significantly thicker, with larger but fewer mesophyll cells with thinner cell walls. Moreover, domesticated genotypes had higher cell wall conductance (gcw) but smaller cytoplasmic conductance (gcyt) than wild genotypes. It appears that domestication in cotton has not generally led to significant improvement in gm, in part because their thinner mesophyll cell walls (increasing gcw) compensate for their lower gcyt, itself due to larger distances between plasmalemma and chloroplast envelopes.
... At the end of the experiment, g m decreased by 83.3% in the S/R20 plants subjected to SD, while no significant differences were observed in R20 between the WW and SD treatments ( Table 2). A strong decrease in g m in S/R20 could be related to the higher SLA exhibited in this cultivar (206.0 ± 7.3 cm 2 g −1 in S/R20 vs. 132.1 ± 4.6 cm 2 g −1 in R20), which could indicate more packaged mesophyll cells inducing greater leaf internal resistance to CO 2 diffusion during drought [32]. This could also explain the stronger reduction in A N in S/R20 (78.6%) than in R20 (69.2%) for SD-treated plants compared to WW plants (see supplementary Figure S1 for changes in photosynthesis-related parameters during the SD experiments in both cultivars). ...
As a consequence of climate change, water scarcity has increased the use of the iso-/anisohydric concept with the aim of identifying anisohydric or drought-tolerant genotypes. Recently, Meinzer and colleagues developed a metric for discriminating between iso- and anisohydric behavior called the hydroscape, which describes a range in which stomata control leaf water potential (Ψ) with decreasing water availability, and it is linked to several water-regulation and drought-tolerance traits. Thus, our objective was to test the usefulness of the hydroscape in discriminating between iso- and anisohydric Prunus dulcis cultivars, a species that is widely cultivated in Mediterranean central Chile due to its ability to withstand water stress. Through a pot desiccation experiment, we determined that the hydroscape was able to discriminate between two contrasting Prunus cultivars; the more anisohydric cultivar had a hydroscape 4.5 times greater than that of the other cultivar, and the hydroscape correlated with other metrics of plant water-use strategies, such as the maximum range of daily Ψ variation and the Ψ at stomatal closure. Moreover, the photosynthesis rates were also differently affected between cultivars. The more isohydric cultivar, which had a smaller hydroscape, displayed a steeper photosynthesis reduction at progressively lower midday Ψ. This methodology could be further used to identify drought-tolerant anisohydric Prunus cultivars.
... Leaf dry mass per unit area (LMA) may increase with leaf age (Xu and Baldocchi 2003, Niinemets et al. 2005, 2006, Ethier et al. 2006, Mediavilla et al. 2011, Noda et al. 2014, Chavana-Bryant et al. 2017, 2019 as a result of the ontogenetic properties of carbon-based compounds accumulating in the mesophyll or cell wall thickening during the structural differentiation and development of leaves. These temporal changes in LMA may influence mesophyll conductance by reducing the rate of CO 2 diffusion inside leaves and therefore limiting the photosynthetic rate and capacity (e.g., V cmax and J max ) , Niinemets et al. 2004. ...
Most leaf functional trait studies in the Amazon basin do not consider ontogenetic variations (leaf age), which may influence ecosystem productivity throughout the year. When leaf age is taken into account, it is generally considered discontinuous, and leaves are classified into age categories based on qualitative observations. Here, we quantified age-dependent changes in leaf functional traits such as the maximum carboxylation rate of Rubisco (Vcmax), stomatal control (Cgs%), leaf dry mass per area (LMA) and leaf macronutrient concentrations for nine naturally growing Amazon tropical trees with variable phenological strategies. Leaf ages were assessed by monthly censuses of branch-level leaf demography; we also performed leaf trait measurements accounting for leaf chronological age based on days elapsed since the first inclusion in the leaf demography, not predetermined age classes. At the tree community scale, a nonlinear relationship between Vcmax and leaf age existed: young, developing leaves showed the lowest mean photosynthetic capacity, increasing to a maximum at 45 days and then decreasing gradually with age in both continuous and categorical age-group analyses. Maturation times among species and phenological habits differed substantially, from 8 ± 30 to 238 ± 30 days, and the rate of decline of Vcmax varied from -0.003 to -0.065 μmol CO2 m-2 s-1 day-1. Stomatal control increased significantly in young leaves but remained constant after peaking. Mass-based phosphorus and potassium concentrations displayed negative relationships with leaf age, while nitrogen did not vary temporally. Differences in life strategies, leaf nutrient concentrations, and phenological types, not the leaf age effect alone, may thus be important factors for understanding observed photosynthesis seasonality in Amazonian forests. Furthermore, assigning leaf age categories in diverse tree communities may not be the recommended method for studying carbon uptake seasonality in the Amazon, since the relationship between Vcmax and leaf age could not be confirmed for all trees.
Çamgiller familyası içinde en büyük kozalağa sahip olan fıstık çamı, son yıllarda sert kabuklu bir meyve türü olarak kabul edilmeye başlanmıştır. Türkiye’de en uygun yetişme koşullarını sağlayan başlıca alanlar İzmir Bergama-Kozak, Aydın-Koçarlı bölgeleridir. Bu çalışmada, Aydın-Koçarlı bölgesinde Orman İşletme Şefliği’ne ait alan ve Taşköy olmak üzere, iki farklı alandaki doğal fıstık çamı ağaçlarının ibrelerinin gelişmesi ve özellikleri incelenmiştir. Bu amaçla; ağaç tacının 1/3’lük üst kısmından ve ışık gören dallardan bir, iki ve üç yaşlı ibre örnekleri, 2021 yılında bir yıllık kozalakların (ülker) oluşmaya başladığı (Mayıs-Haziran ayları) ve bir yıllık kozalakların döküm zamanı olan Ekim ayı olmak üzere 2 farklı dönemde alınmıştır. İbre yaşları ve ağaçlara arasında incelenen özellikler açısından farklılıklar saptanmıştır. İbre yaşı arttıkça uzunluk, kalınlık, yaş ağırlık ve kuru madde miktarında artışlar meydana gelmiştir. Genel olarak OGM alanındaki ağaçların ibrelerinin uzunluk, kalınlık, yaş ağırlık ve kuru madde birikiminin, Taşköy’de bulunan ağaçlara göre daha fazla olduğu belirlenmiştir. Bazı istisnalar hariç iki bölgedeki ağaçlarda da vejetasyon dönemi sonunda. başlangıca göre bütün yaşlarda boy ve kalınlıkta meydana gelen artışlara bağlı olarak ibre ağırlığı ile kuru madde birikiminde de artışlar meydana geldiği tespit edilmiştir.
Deschampsia antarctica is one of the only two native vascular plants in Antarctica, mostly located in the ice-free areas of the Peninsula´s coast and adjacent islands. This region is characterized by a short growing season, frequent extreme climatic events and soils with reduced nutrient availability. However, it is unknown whether its photosynthetic and stress tolerance mechanisms are affected by the availability of nutrients to deal with this particular environment. We studied the photosynthetic, primary metabolic and stress tolerance performance of D. antarctica plants growing on three close sites (<500 m) with contrasting soil nutrient conditions. Plants from all sites showed similar photosynthetic rates, but mesophyll conductance and photobiochemistry were more limiting (ca. 25%) in plants growing on low-nutrient availability soils. Additionally, these plants showed higher stress levels and larger investments in photoprotection and carbon pools, most likely driven by the need to stabilize proteins, membranes and remodel cell walls. Contrarily, when nutrients were readily available, plants shifted their carbon investment towards amino acids related to osmoprotection, growth, antioxidants and polyamines, leading to vigorous plants without appreciable levels of stress. Taken together, these findings demonstrate that D. antarctica displays differential physiological performances to cope with adverse conditions depending on resource availability, allowing it to maximize stress tolerance without jeopardizing photosynthetic capacity.
Crop photosynthesis (A) and productivity are often limited by a combination of nutrient stresses, such that changes in the availability of one nutrient may affect that of another nutrient, in turn influencing A. In this study, we examined the synergistic effects of phosphorus (P) and potassium (K) on leaf A in a nutrient amendment experiment, in which P and K were added individually or in combination to Brassica napus grown under P and K co‐limitation. The data revealed that P addition gradually removed the dominant limiting factor (i.e., P) and improved leaf A. Strikingly, the addition of K synergistically improved gross P uptake, mainly by boosting plant growth, and compensated the physiological demand for P by prioritising investment in metabolic P pools (P‐containing metabolites and inorganic phosphate, Pi). The enlarged pool of metabolically active P was partially associated with upregulation of Pi regeneration through release from triose phosphates rather than replacement of P‐containing lipids. This process mitigated P restrictions on A by maintaining the ATP/NADPH and NADPH/NADP+ ratios and increasing the content and activity of Rubisco. Our findings demonstrate that sufficient K increased Pi‐limited A by enhancing metabolic P fractions and Rubisco activity. Thus, ionic synergism may be exploited to mitigate nutrient‐limiting factors to improve crop productivity.
There is a controversy regarding when it is appropriate to apply the irrigation restriction in almond trees (Prunus dulcis Mill.) to save water without penalizing yield. We hypothesized that knowing when plants demand fewer photoassimilates would be a good indicator of less sensitivity of the crop to water deficit. One parameter that defines the photosynthetic capacity is the triose phosphate utilization (TPU). Due to its connection to the export of sugars from the leaves to other sink organs, it is a good candidate for being such an indicator. The objective was to analyze the seasonal evolution of the photosynthetic capacity of three almond cultivars (cvs. Guara, Marta and Lauranne) subjected to water stress during vegetative, kernel-filling, and postharvest stages. Two sustained deficit irrigation (SDI) treatments (SDI75 and SDI65 with water reductions of 25% and 35%, respectively) and a control treatment (FI) consisting on full irrigated trees were applied. The response of curves AN-Ci was analyzed to assess the maximum carboxylation rate (Vcmax), maximum rate of electron transport (Jmax), TPU and mesophyll conductance to CO2. Additionally, leaf water potential and yield were measured. Our experimental findings showed any significant differences in the variables analyzed among cultivars and irrigation treatments. However, consistent differences arose when the results were compared among the phenological stages. During the kernel-filling and the postharvest stages, a progressive limitation by TPU was measured, suggesting that the demand for photoassimilates by the plant was reduced. This result was supported by the correlation found between TPU and fruit growth rate. As a consequence, a downregulation in Jmax and Vcmax was also measured. This study confirms that the kernel-filling stage might be a good time to apply a reduction in the irrigation and suggests a method to detect the best moments to apply a regulated deficit irrigation in almond trees.
Drought stress significantly affects cotton’s net photosynthetic rate (A) by restraining stomatal (gs) and mesophyll conductance (gm) as well as perturbing its biochemical process, resulting as a consequence in yield reductions. Despite the significant progress in dissecting effects of drought on photosynthesis, the variability observed in cotton’s gm, and the mechanisms contributing to that variability under dynamic drought stress conditions are poorly understood. For that reason, a controlled‐environment experiment with two cotton genotypes (Dexiamian 1, Yuzaomian 9110), three water levels [soil relative water content: control (75±5)%, moderate drought (60±5)%, severe drought (45±5)%], and two drought durations (10, 31 days) was conducted. The results indicated that cotton boll biomass was significantly decreased under 10‐day severe drought and 31‐day moderate and severe drought. Decreases in gs were later accompanied by decreases in gm and further combined with reductions in electron transport rate, as drought stress progressed in duration and severity, ultimately resulting in significant reductions in A of subtending leaf. Stomatal and mesophyll conductance constraints were the primary factors limiting photosynthesis, while biochemical constraints decreased, as drought stress progressed. Considering gm, its decline was ascribed to increases in the diffusion resistance of CO2 through cytoplasm (rcyt), under short‐ or long‐term drought, as well as to increases in leaf dry mass (LMA), and decreases in the chloroplast surface area exposed to intercellular air space (Sc/S), under long‐term drought. It was concluded that A could be enhanced, under dynamic drought stress conditions, by increasing gm through increasing Sc/S and reducing LMA and rcyt.
Islands tend to be more prone to plant invasions than mainland regions, with the Mediterranean ones not being an exception. So far, a large number of studies on comparing leaf morphological and physiological traits between native and non-native plants in Mediterranean environments have been performed, although none of them on Mediterranean islands. To fill this gap, this study focuses on 14 plant species grown in a controlled growth chamber in the absence of stress. The goal was (1) to differentiate leaf morpho-physiological traits between native and non-native plants on a Mediterranean island and (2) to deepen in the underlying causes of the differential photosynthetic traits displayed by non-native species. Results showed that in Mediterranean islands, non-native plant species show on average larger values of net CO2 assimilation, stomatal conductance (gm), photosynthetic nitrogen-use efficiency, among others, and lower leaf mass per area (LMA) and leaf thickness, compared to the native species. Among the assessed traits, this study reports for the first time larger gm, and lower mesophyll conductance limitation in non-native species, which seems to be linked to their lower LMA. These novel traits need to be added to the ‘leaf physiological trait invasive syndrome’. It was also found that on a Mediterranean island, native and non-native species are placed on opposite sides of the leaf economics spectrum, with non-native species being placed on the ‘‘fast-return’’ end. In conclusion, this study demonstrates that non-native species inhabiting a Mediterranean island possess distinct leaf morphological and physiological traits compared to co-occurring native species, at least during the favorable growth season, which increases the chances of a successful invasion.
Two main leaf types are recognized among vascular plant species: compound and simple. Compound leaves are believed to be photosynthetically more productive than simple ones, by diluting mass tissue in more projected area. Conversely, simple leaves are believed to be more stress tolerant by packing mass tissue in less projected area during stress like drought. Nevertheless, convective cooling is more efficient in compound than simple leaves, a process that could alleviate water loss in drought periods. In Central Chile, woody species with simple and compound leaves coexist. This zone is facing a mega-drought event, causing browning and tree mortality. However, photosynthetic limitations on both types of leaves in drought conditions have not been addressed so far. We measured photosynthetic limitations in well-watered and drought conditions in three compound and three simple leaf species, and drought response ratio were obtained. We hypothesized that with no water limitation compound leaf species will show higher net photosynthesis (A N ) than simple leaf species associated with a higher mesophyll conductance (g m ). Nevertheless, opposite results are expected for simple leaves because their stress-tolerant physiology, showing fewer changes in their photosynthetic traits. We found that (g m ) and (A N ) were larger in compound leaves in well-watered conditions. Under drought conditions, both types of leaves were negatively affected despite foliar temperature in compound leaf species was 4°C lower. Our result suggests that regardless leaf shape matorral species in Central Chile will be seriously affected in their A N due to the megadrought currently affecting this zone.
The foliar photosynthetic acclimation to prolonged elevated CO2 has been studied in many ways, but the quantification of photosynthetic acclimation through the limitation of stomatal conductance (gs), mesophyll conductance (gm) and biochemical capacity (Vcamx) is scarce. To quantify photosynthetic acclimation under elevated CO2, a japonica rice cultivar ‘Nanjing 9108’ was grown at two CO2 levels—ambient CO2 (a[CO2]) and a[CO2] +200 µmol mol‒1 (e[CO2]) using open top chamber facility. We measured the response of net photosynthetic rate (An) to CO2 at Rubisco (Cc) at jointing, flowering and filling stages based a biochemical C3‐photosynthesis model. Measurements at the same CO2 concentration showed that the An under e[CO2] was significantly lower than that under a[CO2] at three developmental stages, suggesting the occurrence of acclimation of photosynthesis. The photosynthetic acclimation is associated with the decrease in gm, gs and Vcmax, and gm mainly limits photosynthesis. The contribution of gm, gs and Vcamx limitation to photosynthetic acclimation averaged 65%, 25% and 10% of the total reduction in An. Our findings demonstrate gm is the major driver of photosynthetic acclimation and highlight the role of gm under e[CO2] in rice.
The CO2 transfer conductance in leaves quantifies the ease with which CO2 can diffuse from sub-stomatal cavities to sites of carboxylation within the chloroplast. The aim of this work was to test the hypothesis that the CO2 transfer conductance is proportional to the surface area of chloroplasts exposed to intercellular airspaces. We compared two genotypes, wild-type and transgenic tobacco, that had been transformed with an antisense gene directed at the mRNA of the Rubisco small subunit. Transgenic tobacco had lower rates of CO2 assimilation than wild-type but similar chlorophyll contents. Leaf anatomy was altered by growing plants in two different environments: a high daily irradiance in a growth cabinet (12 h photoperiod of 1 mmol quanta m-2 s-1) and a sunlit glasshouse. The growth cabinet gave at least twice the daily irradiance compared to the glasshouse. The CO2 transfer conductance was calculated from combined measurements of gas exchange and carbon isotope discrimination measured in 2% oxygen. Following gas exchange measurement, leaves were sampled for biochemical and anatomical measure- ment. In transgenic tobacco plants, Rubisco content was 35% of that found in the wild-type tobacco, the CO2 assimilation rate was 50% of the wild-type rate and the chlorophyll content was unaltered. While leaf mass per unit leaf area of transgenic tobacco was 82% of that of the wild-type, differences in leaf thickness and surface area of mesophyll cells exposed to intercellular airspace per unit leaf area (Smes) were small (92 and 87% of wild-type, respectively). Leaves grown in the growth cabinet under high daily irradiance were thicker (63%), had a greater Smes (41%) due to the development of thicker palisade tissue, had higher photosynthetic capacity (27%) and contained more chlorophyll (58%) and Rubisco (77%), than leaves from plants grown in the glasshouse. Irrespective of genotype or growth environment, CO2 transfer conductance varied in proportion to surface area of chloroplasts exposed to intercellular airspaces. While the method for calculating CO2 transfer conductance could not distinguish between limitations due to the gas or liquid phases, there was no reduction in CO2 transfer conductance associated with more closely packed cells, thicker leaves, nor with increasing chloroplast thickness in tobacco.
We examined the changes in leaf anatomy and some physiological characteristics
during leaf expansion and maturation. Three deciduous tree species having
different types of shoot phenology, maple (Acer mono
Maxim.; ‘flush’ type), alder
(Alnus japonica(Thunb.) Steud.; ‘successive’
type), and Japanese poplar (Populus maximowiczii A.
Henry; ‘successive’ type), were studied. Leaf CO
2 assimilation rate at high irradiance
(P max) and CO
2 transfer conductance inside the leaf
(g i) varied significantly with
leaf development. There were strong positive relationships between
P max) and g
i for all of the species. The variations in
g i were partly related to those
in the surface area of chloroplasts facing the intercellular airspaces, while
some other factors that related to liquid phase conductance may also
contribute to the variation in g i
. The developments of mesophyll cells were accompanied by the concomitant
increase in chloroplast and Rubisco content in Alnus and
Populus (successive types).
Various aspects of the biochemistry of photosynthetic carbon assimilation in C3 plants are integrated into a form compatible with studies of gas exchange in leaves. These aspects include the kinetic properties of ribulose bisphosphate carboxylase-oxygenase; the requirements of the photosynthetic carbon reduction and photorespiratory carbon oxidation cycles for reduced pyridine nucleotides; the dependence of electron transport on photon flux and the presence of a temperature dependent upper limit to electron transport. The measurements of gas exchange with which the model outputs may be compared include those of the temperature and partial pressure of CO2(p(CO2)) dependencies of quantum yield, the variation of compensation point with temperature and partial pressure of O2(p(O2)), the dependence of net CO2 assimilation rate on p(CO2) and irradiance, and the influence of p(CO2) and irradiance on the temperature dependence of assimilation rate.
Measurements of CO2 and water vapour exchange by leaves were combined with measurements of carbon isotope composition (13C/12C) of CO2 in the air passing over the leaf. Carbon isotope discrimination during CO2 uptake was determined from the difference in carbon isotope composition of the air leaving the leaf chamber with or without a leaf enclosed. Leaves of wheat plants grown with different nitrogen nutrition and leaves of several other species were examined.
The measurements, made at different irradiances for a given leaf, showed that carbon isotope discrimination was strongly correlated with the rate of CO2 assimilation as well as the ratio of intercellular to ambient partial pressure of CO2, pI/pa. A function relating carbon isotope discrimination to the rate of CO2 assimilation was used to estimate the CO2 transfer conductance, gw, from the substomatal cavities to the sites of carboxylation for individual leaves. The photosynthetic capacity correlated with the CO2 transfer conductance, gw, and the average ratio of chloroplastic to intercellular partial pressure of CO2, pI/pa, was 0.7. This means that in general under high irradiance, the ratio of chloroplastic to ambient partial pressure of CO2 is about 0.5. In wheat, variation in gw was correlated with the chloroplast surface area appressing intercellular airspaces.
Bringing together leaf trait data spanning 2,548 species and 175 sites we describe, for the first time at global scale, a universal spectrum of leaf economics consisting of key chemical, structural and physiological properties. The spectrum runs from quick to slow return on investments of nutrients and dry mass in leaves, and operates largely independently of growth form, plant functional type or biome. Categories along the spectrum would, in general, describe leaf economic variation at the global scale better than plant functional types, because functional types overlap substantially in their leaf traits. Overall, modulation of leaf traits and trait relationships by climate is surprisingly modest, although some striking and significant patterns can be seen. Reliable quantification of the leaf economics spectrum and its interaction with climate will prove valuable for modelling nutrient fluxes and vegetation boundaries under changing land-use and climate.
This paper addresses two main questions. First, can evergreen foliage that has been structurally determined as sun foliage acclimate physiologically when it is shaded? Second, is this acclimation independent of the foliage ageing process and source-sink relations? To investigate these questions, a shading and debudding experiment was established using paired branches on opengrown Abies amabilis trees. For each tree, one branch was either shaded, debudded, or both, from before budbreak until the end of summer, while the other branch functioned as a control. Foliage samples were measured both prior to and during treatment for photosynthesis at light saturation (A
max), dark respiration, nitrogen content, chlorophyll content, chlorophyll-to-nitrogen ratio and chlorophyll a:b ratio. All age classes of foliage responded similarly during the treatment, although pre-treatment values differed between age classes. Within 1 month after the treatment began, A
max was lower in shaded foliage and remained lower throughout the treatment period. For debudded branches, A
max was lower than the controls only during active shoot elongation. At the end of the treatments in September, A
max in shade-treated sun foliage matched the rates in the true shade-formed foliage, but nitrogen remained significantly higher. By 1.5 months after treatment, chlorophyll content in shaded foliage was higher than in controls, and the chlorophyll a:b ratio was lower for the shaded foliage. On debudded branches, chlorophyll content and chlorophyll a:b ratio were similar to the values in control samples. Shading lowered the rate of nitrogen accumulation within a branch, while removing debudding decreased the amount of sequestered N that was exported from the older foliage to supply new growth. By September, chlorophyll content in shade-treated foliage was higher than that in the control sun foliage or in true shade foliage. The chlorophyll increase as a result of shading was unexpected. However, the chlorophyll-to-nitrogen ratio was identical for the shade-treated sun foliage and the true shade foliage while being significantly lower than the control sun foliage. It appears that acclimation to shading in mature foliage involves a reallocation of nitrogen within the leaf into thylakoid proteins. A redistribution of resources (nitrogen) among leaves is secondary and appears to function on a slower time scale than reallocation within the leaf. Thus, A. amabilis foliage that is structurally determined as sun foliage can acclimate to shade within a few months; this process is most likely independent of ageing and is only slightly affected by source-sink relations within a branch.
Changes in net photosynthetic rate on a leaf area basis and anatomical properties during leaf development were studied in an evergreen broad-leaved tree, Castanopsis sieboldii and an annual herb, Phaseolus vulgaris. In C. sieboldii, surface area of mesophyll cells facing the intercellular air spaces on a leaf area basis (Smes) was already considerable at the time of full leaf area expansion (FLE). However, surface area of chloroplasts facing the intercellular air spaces on a leaf area basis (Sc), and chlorophyll and Rubisco contents on a leaf area basis increased to attain their maximal values 15–40 d after FLE. In contrast, in P. vulgaris, chloroplast number on a leaf area basis, Sc and Smes at 10 d before FLE were two to three times greater than the steady-state levels attained at around FLE. In C. sieboldii, the internal CO2 transfer conductance (gi) slightly increased for 10 d after FLE but then decreased toward the later stages. Limitation of photosynthesis by gi was only about 10% at FLE, but then increased to about 30% at around 40 d after FLE. The large limitation after FLE by gi was probably due to the decrease in CO2 concentration in the chloroplast caused by the increases in thickness of mesophyll cell walls and in Rubisco content per chloroplast surface area. These results clearly showed that: (1) in C. sieboldii, chloroplast development proceeded more slowly than mesophyll cell expansion and continued well after FLE, whereas in P. vulgaris these processes proceeded synchronously and were completed by FLE; (2) after FLE, photosynthesis in leaves of C. sieboldii was markedly limited by gi. From these results, it is suggested that, in the evergreen broad-leaved trees, mechanical protection of mesophyll cells has priority over the efficient CO2 transfer and quick construction of the chloroplasts.
Spatial and temporal changes in canopy structure were studied in 1988 and 1989 in a Mediterranean Quercus ilex forest in north-eastern Spain. Due to differences in precipitation patterns the 1989 growing season was drier than the 1988 growing season. Sampling was conducted in parallel at two sites which represent endpoints along a slope gradient within a watershed (ridge top at 975 m, and valley bottom at 700 m). At both sites, similar inter-annual changes in canopy structure were observed in response to differences in water availability. Samples harvested in the upper 50 cm of the canopy during 1989 exhibited a decrease in both average leaf size and the ratio of young to old leaf and stem biomass relative to samples obtained in 1988. At the whole canopy level, a decrease in leaf production efficiency and an increase in the stem to leaf biomass ratio was observed in 1989. Temporal changes in canopy leaf area index (LAI) were not statistically significant. Average LAI values of Q. ilex at the two sites were not significantly different despite differences in tree stature and density (4.6 m2 m–2 at the ridge top, and 5.3 m2 m–2 at the valley bottom). Vertical distribution of leaves and stems within the canopy was very similar at the two locations, with more than 60% of the total LAI in the uppermost metre of the canopy. The possible significance of such an LAI distribution on the canopy carbon budget is discussed.
Acquisition of CO2 by higher plants involves CO2 diffusion from the air into leaves and, ultimately, into chloroplasts. There, fixation of CO2 into organic compounds creates the concentration gradient which drives CO2 diffusion. CO2 encounters many obstructions along its diffusion path toward chloroplasts. The diffusion resistances attributable to boundary layer and stomata are shared with the opposing flux of water leaving the leaf. Once in the substomatal cavities, however, CO2 faces additional resistances since it has to cross walls and membranes to reach the chloroplasts. We follow the CO2 molecule from the air through the boundary layer, stomata and, finally, the mesophyll. After providing diverse anatomical examples at each level, we review the current understanding about the subtle balance which plants maintain between water loss and CO2 acquisition.
Stomatal responses to many environmental variables are well known, despite our lack of understanding of the underlying mechanisms. Techniques areavailable that allow accurate measurements of conductances through the boundary layer and stomata. The estimation of conductance through the mesophyll, however, has not been feasible until the recent development of rapid measurements of isotopic discrimination and chlorophyll fluorescence. We discuss the principles which allow the estimation of internal conductance based on these techniques and the data available. Both stomatal conductance and internal conductance correlate strongly with photosynthetic capacity and are of similar magnitude. However, stomatal conductance can vary within minutes in response to changes in the environment. Internal conductance, on the other hand, seems to be stable over several days and depends on anatomical properties of the leaf. We close considering the special case of photosynthesis where spatial compartmentation and biochemical mechanisms of CO2 concentration add complexity to the estimation of internal conductance.
Transgenic tobacco (Nicotiana tabacum L. cv. W38) with an antisense gene directed against the mRNA of the ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) small subunit was used to determine the kinetic properties of Rubisco in vivo. The leaves of these plants contained only 34% as much Rubisco as those of the wild type, but other photosynthetic components were not significantly affected. Consequently, the rate of CO2 assimilation by the antisense plants was limited by Rubisco activity over a wide range of CO2 partial pressures. Unlike in the wild-type leaves, where the rate of regeneration of ribulose bisphosphate limited CO2 assimilation at intercellular partial pressures above 400 ubar, photosynthesis in the leaves of the antisense plants responded hyperbolically to CO2, allowing the kinetic parameters of Rubisco in vivo to be inferred. We calculated a maximal catalytic turnover rate, kcat, of 3.5+0.2 mol CO2(mol sites)–1s–1 at 25 C in vivo. By comparison, we measured a value of 2.9 mol CO2(mol sites)–1–1 in vitro with leaf extracts. To estimate the Michaelis-Menten constants for CO2 and O2, the rate of CO2 assimilation was measured at 25 C at different intercellular partial pressures of CO2 and O2. These measurements were combined with carbon-isotope analysis (13C/12C) of CO2 in the air passing over the leaf to estimate the conductance for transfer of CO2 from the substomatal cavities to the sites of carboxylation (0.3 molm–2s–1bar–1) and thus the partial pressure of CO2 at the sites of carboxylation. The calculated Michaelis-Menten constants for CO2 and O2 were 259 57 bar (8.61.9M) and 179 mbar (226 M), respectively, and the effective Michaelis-Menten constant for CO2 in 200 mbar O2 was 549 bar (18.3 M). From measurements of the photocompensation point (* = 38.6 ubar) we estimated Rubisco's relative specificity for CO2, as opposed to O2 to be 97.5 in vivo. These values were dependent on the size of the estimated CO2-transfer conductance.
Light that plants encounter in the environment originates mostly from the sun. The spectral properties of sunlight fundamentally
reflect the surface temperature of the sun (∼5800 K). However, the solar spectrum is modified by the earth’s atmosphere due
to absorption by water and CO2, and by scattering. Light can either be expressed in terms of an energy flux or a quantum flux. The energy content of a quanta
depends on its wavelength, decreasing as wavelength increases. Energy flux (E, W m−2) can be calculated from quantum flux (I, mol m−2 s−1) for a given wavelength (λ, m) with the following equation: E = IN
0
hc/λ where N
0
is Avogadro’s number (6.02 × 1023), h is Planck’s constant (6.63 × 10−34 J s photon−1) and c is the speed of light (3 × 108 m s−1). For example, 1 µmol quanta m−2 s−1 of 400 nm light is equivalent to 0.3 W m−2, while for 700 nm light it is 0.17 W m−2.
We investigated the adaptation of three spruce species (Picea glehnii Masters, P. jezoensis Carr. and P. abies Karst.) to growth in northern Japan on serpentine soils (characterized by high concentrations of heavy metals and Mg, a low Ca/Mg ratio and low fertility) and fertile brown forest soils. Among species, seedling survival on serpentine soil was highest in P. glehnii. Shoot growth of P. glehnii was similar whether grown on serpentine or brown forest soil, whereas shoot growth of the other species was significantly less on serpentine soil than on brown forest soil. On serpentine soil, needle life span of P. glehnii was at least 3 years longer than that of the other two species. Needle area per shoot of P. glehnii was significantly higher on serpentine soil than on brown forest soil up to a shoot age of 8 years. In all three species, light-saturated photosynthetic rate (Pmax) decreased with needle age independently of soil type. However, on serpentine soil, Pmax in P. glehnii was higher, particularly in older needles, than in the other species. Furthermore, on serpentine soil, needle concentrations of nitrogen and phosphorus were higher in P. glehnii than in the other species. We conclude that P. glehnii is better adapted to serpentine soil than P. jezoensis and P. abies at least in part because of its greater needle life span and higher needle nutrient concentrations.
Leaves are beautifully specialized organs that enable plants to intercept light necessary for photosynthesis. The light is dispersed among a large array of chloroplasts that are in close proximity to air and yet not too far from vascular tissue, which supplies water and exports sugars and other metabolites. To control water loss from the leaf, gas exchange occurs through pores in the leaf surface, stomata, which are able to rapidly change their aperture. Once inside the leaf, CO, has to diffuse from the intercel- lular air spaces to the sites of carboxylation in the chloro- plast (for C, species) (Fig. 1) or the cytosol (for C, species). These internal diffusion paths are the topic of this article. There are several reasons why internal diffusion is of interest. First, Rubisco has a poor affinity for CO, and operates at only a fraction of its catalytic capacity in C, leaves. The CO, gradient within the leaf thus affects the efficiency of Rubisco and the overall nitrogen use efficiency of the leaf. Second, prediction of photosynthetic rates of leaves from their biochemical properties requires a good estimate of the partial pressure of CO, at the sites of carboxylation, pc. Third, internal resistance to CO, diffu- sion results in a lower pc and reduces carbon gain relative to water loss during photosynthesis (water-use efficiency). Considerable effort is being invested selecting and identi- fying plants with improved water-use efficiency using the surrogate measure of carbon isotope discrimination, A, of plant dry matter (Ehleringer et al., 1993). The ratio of intercellular to ambient CO, partial pressure, pi/p,, and A are both linearly related to water-use efficiency if pc/pi is constant. To date, we have little knowledge of genetic variation in pc/pi. Until recently, it was not possible to directly measure the gradient in CO, partial pressure to the sites of carboxyla- tion. The gradient could be inferred from a theoretical analysis of the diffusion pathway, but because several steps have unknown permeability constants, the values are un- certain. Opinion has oscillated from the existence of large to small gradients over the last 30 years. There are now two techniques that enable the gradient to be measured in C, leaves. After describing these techniques, we will consider diffusion through intercellular air spaces and diffusion across cell walls and liquid phase to sites of carboxylation. Finally, we will examine CO, diffusion into mesophyll cells and across the bundle sheath in C, leaves.
Dark respiration in light as well as in dark was estimated for attached leaves of an evergreen (Heteromeles arbutifolia Ait.) and a deciduous (Lepechinia fragans Greene) shrub species using an open gas-exchange system. Dark respiration in light was estimated by the Laisk method. Respiration rates in the dark were always higher than in the light, indicating that light inhibited respiration in both species. The rates of respiration in the dark were higher in the leaves of the deciduous species than in the evergreen species. However, there were no significant differences in respiration rates in light between the species. Thus, the degree of inhibition of respiration by light was greater in the deciduous species (62%) than in the evergreen species (51%). Respiration in both the light and darkness decreased with increasing leaf age. However, because respiration in the light decreased faster with leaf age than respiration in darkness, the degree of inhibition of respiration by light increased with leaf age (from 36% in the youngest leaves to 81% in the mature leaves). This suggests that the rate of dark respiration in the light is related to the rate of biosynthetic processes. Dark respiration in the light decreased with increasing light intensity. Respiration both in the light and in the dark was dependent on leaf temperature. We concluded that respiration in light and respiration in darkness are tightly coupled, with variation in respiration in darkness accounting for more than 60% of the variation in respiration in light. Care must be taken when the relation between respiration in light and respiration in darkness is studied, because the relation varies with species, leaf age, and light intensity.
The capacity to conduct CO2 from the intercellar spaces in leaves to the site of fixation (mesophyll conductance, gm) may pose a significant limitation to photosynthesis. Dacrydium cupressinum Sol. ex Lamb, (rimu), a native conifer of New Zealand, and other members of the Podocarpaceae evolved during the Jurassic when the partial pressure of CO2 exceeded 200 Pa. This species has low rates of photosynthesis and high levels of leaf nitrogen, which have led to the hypothesis that low gm restricts photosynthesis. Mesophyll conductance was estimated from gas-exchange and fluorescence measurements for this and other co-occurring tree species [Prumnopitys ferruginea D. Don (miro), Weinmannia racemosa L.f. (kāmahi), Meterosideros umbellata Cav. (rata)]. Pinus radiata D. Don (radiata pine) and Phaseolus vulgaris L. (bean) were included to provide comparisons with a rapidly growing tree and herbaceous plant with relatively high photosynthetic rates. Mesophyll conductance was not statistically different among indigenous tree species but was lowest for D. cupressinum. This species also had the lowest ratio of mesophyll to stomatal conductance, gm/gst and was the only species where the decline in partial pressure of CO 2 was greater from the intercellular air space to the site of fixation (16.3 Pa) than between the bulk air and the intercellular spaces (8.8 Pa), providing support for the hypotheses that low gm limits photosynthesis in this species. As a group, conifers had marginally lower g m and gm/gst ratio than angiosperms, but this difference was strongly influenced by the high values for Phaseolus vulgaris. That co-occurring members of the Podocarpaceae operated differently suggests that low gm may reflect a response to evolutionary pressures other than high atmospheric CO2 partial pressure.
Ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco; EC 4.1.1.39) has played a central role in our understanding of chloroplast biogenesis and photosynthesis. In particular, its catalysis of the rate-limiting step of CO_2 fixation, and the mutual competition of CO_2 and O_2 at the active site, makes Rubisco a prime focus for genetically engineering an increase in photosynthetic productivity. Although it remains difficult to manipulate the chloroplast-encoded large subunit and nuclear-encoded small subunit of crop plants, much has been learned about the structure/function relationships of Rubisco by expressing prokaryotic genes in Escherichia coli or by exploiting classical genetics and chloroplast transformation of the green alga Chlamydomonas reinhardtii. However, the complexity of chloroplast Rubisco in land plants cannot be completely addressed with the existing model organisms. Two subunits encoded in different genetic compartments have coevolved in the formation of the Rubisco holoenzyme, but the function of the small subunit remains largely unknown. The subunits are posttranslationally modified, assembled via a complex process, and degraded in regulated ways. There is also a second chloroplast protein, Rubisco activase, that is responsible for removing inhibitory molecules from the large-subunit active site. Many of these complex interactions and processes display species specificity. This means that attempts to engineer or discover a better Rubisco may be futile if one cannot transfer the better enzyme to a compatible host. We must frame the questions that address this problem of chloroplast-Rubisco complexity. We must work harder to find the answers.
The substrate specificity factor, V cKo/VoKc, of spinach (Spinacia oleracea L.) ribulose 1,5-bisphosphate carboxylase/oxygenase was determined at ribulosebisphosphate concentrations between 0.63 and 200 μM, at pH values between 7.4 and 8.9, and at temperatures in the range of 5° C to 40° C. The CO2/O2 specificity was the same at all ribulosebisphosphate concentrations and largely independent of pH. With increasing temperature, the specificity decreased from values of about 160 at 5° C to about 50 at 40° C. The primary effects of temperature were on K c [Km(CO2)] and V c [Vmax (CO2)], which increased by factors of about 10 and 20, respectively, over the temperature range examined. In contrast, K o [Ki (O2)] was unchanged and V o [Vmax (O2)] increased by a factor of 5 over these temperatures. The CO2 compensation concentrations (Γ) were calculated from specificity values obtained at temperatures between 5° C and 40° C, and were compared with literature values of Γ. Quantitative agreement was found for the calculated and measured Γ values. The observations reported here indicate that the temperature response of ribulose 1,5-bisphosphate carboxylase/oxygenase kinetic parameters accounts for two-thirds of the temperature dependence of the photorespiration/photosynthesis ratio in C3 plants, with the remaining one-third the consequence of differential temperature effects on the solubilities of CO2 and O2.
The Mediterranean-type climates can be generally considered a transition between dry tropical and temperate climates. It is generally accepted that they are characterized by a distinctive annual climatic sequence in which a hot, dry summer alternates with a cold, humid period lasting 5–10 months, from fall through winter to spring. The availability of both water and soil nutrients appears to be the major environmental factor affecting the nature and distribution of vegetation, and exerting the strongest control on plant productivity. Vegetation is characterized by the dominance of trees and woody shrubs with small, evergreen, sclerophyllous leaves. In any case, the photosynthetic performance of the Mediterranean species does not differ particularly from that of species from other biomes. Plants acclimate to decreased photosynthetically active radiation (PAR) availability within the canopy producing a gradient of leaves that are morphologically as well as physiologically distinct. Differences in photosynthetic capacity of leaves exposed to different PAR may arise from variation in both leaf mass per area (LMA) and differential allocation to photosynthetic enzymes as compared to light-harvesting machinery, both of which contribute to variation in area-based leaf nitrogen content (N). The results from this chapter show that the Mediterranean evergreen oak canopies and probably all other Mediterranean-type ecosystems are in some way nearly optimal because of nonuniformity in leaf N, and LMA improves canopy carbon gain. Plant–water relations have shown that drought tolerance and stomatal sensitivity are not necessarily related to roofing depth, to soil moisture resources available to a plant, or to the degree of seasonal water stress experienced by the plant.
ABSTRACT Anatomy and some physiological characteristics of the leaves in Polygonum cuspidatum Sieb. et Zucc., a dioecious clonal herb, were compared between two populations, one from a lowland in Shizuoka City (10 m above sea level), and another from a highland on Mt. Fuji (2500 m above sea level). Leaf mass per area (LMA) of the highland plants was about twice that of the lowland plants. The greater leaf thickness, thicker mesophyll cell walls and higher mesophyll cell density in the highland leaves contributed to the larger LMA. Although mesophyll area exposed to intercellular airspaces was greater in the highland leaves than in the lowland leaves by 30%, the surface area of chloroplasts facing intercellular airspaces was similar between these leaves. CO2 transfer conductance inside the leaf (gi) of the highland leaves (0·75 μmol m−2 s−1 Pa−1) is the lowest recorded for herbaceous plants and was only 40% of that in the lowland leaves. On the other hand, the difference in stomatal conductance was small. δ13C values in the leaf dry matter were greater in the highland leaves by 4‰. These data and the estimation of CO2 partial pressures in the intercellular air spaces and in the chloroplast suggested that the greater dry matter δ13C in the highland leaves, indicative of lower long-term ratio of the chloroplast stroma to the ambient CO2 partial pressures, would be mainly attributed to their lower gi.
The changes in the mineral nutrient content of the leaves of an evergreen species, the cork oak (Quercus suber L.), were investigated to assess the possibilities of a diagnosis of the mineral nutrition of this forest species. A comprehensive pattern of change in the leaf contents of N, P, and Ca was then put forward from the data obtained. Among the time intervals that are most favorable to analyses, the end of the vegetative rest period, in January, was investigated more precisely. The variation coefficients of the leaf contents measured tree by tree were determined for a number of nutrients (N, P, K, Ca, Mg, Fe, Cu, Zn, Mn, B, Al, and Cl). The foliar analyses carried out on 7‐ to 10‐month old leaves in stands submitted to various forest management practices led to the characterization of significant differences in P, Ca and Mn leaf contents in relation to the treatments applied.
In the past, ecophysiologically oriented photosynthesis research has been governed by gas-exchange measurements, mainly involving sophisticated (and costly) systems for simultaneous detection of CO2 uptake and H2O evaporation (see, e.g., Field et al. 1989). With the help of these methods, fundamental knowledge on in situ photosynthesis has been gained. Only recently, progress has been made in the development of alternative practical methods for nonintrusive assessment of in vivo photosynthesis which have the potential of not only evaluating overall quantum yield and capacity, but also allowing insights into the biochemical partial reactions and the partitioning of excitation energy (see, e.g., Snel and van Kooten 1990). As a consequence, photosynthesis research at the level of regulatory processes has been greatly stimulated, leading to important new concepts (see reviews by Foyer et al. 1990; Demmig-Adams 1990; Melis 1991; Allen 1992). In particular, chlorophyll fluorescence has evolved as a very useful and informative indicator for photosynthetic electron transport in intact leaves, algae, and isolated chloroplasts (reviews by Briantais et al. 1986; Renger and Schreiber 1986; Schreiber and Bilger 1987, 1992; Krause and Weis 1991; Karukstis 1991).
Leaf dry mass per unit area (LMA) is a product of leaf thickness (T) and of density (D). Greater T is associated with greater foliar photosynthetic rates per unit area because of accumulation of photosynthetic compounds; greater D results in decreased foliage photosynthetic potentials per unit dry mass because of lower concentrations of assimilative leaf compounds and decreases in intercellular transfer conductance to CO2. To understand the considerable variation in T and D at the global scale, literature data were analyzed for 558 broad-leaved and 39 needle-leaved shrubs and trees from 182 geographical locations distributed over all major earth biomes with woody vegetation. Site climatic data were interpolated from long-term world climatologies (monthly precipitation, surface temperature) or modeled using the Canadian Climate Center Model (monthly global solar radiation). Influences of total annual precipitation (W-T), precipitation of the driest month (W-min), monthly mean precipitation of the three driest months in the year (W-3min), highest monthly precipitation (W-max), precipitation index ([W-max - W-min]/W-T), mean, minimum, and maximum annual monthly temperatures, and daily annual mean global solar radiation (R) on LMA, D, and T were tested by simple and multiple linear and log-linear regression analyses. In broad-leaved species, LMA and T increased with increasing R and mean temperature and scaled weakly and negatively with precipitation variables, but D was negatively related only to precipitation. Similar relationships were also detected in needle-leaved species, except that, in multiple regression analysis, precipitation did not significantly influence leaf thickness, and R was positively related to D. Given that increases in LMA and T are compatible with enhanced photosynthetic capacities per unit leaf area, but also with greater costs for construction of unit surface area, positive effects of solar irradiance and surface temperature on these variables are indicative of shorter leaf pay-back times in conditions of higher irradiance and temperature allowing construction of leaves with higher photosynthetic potential. To gain insight into the scaling of leaf density with site aridity, correlations of D with the leaf elastic modulus close to full turgor (epsilon) and with the leaf osmotic potentials (pi) at full and zero turgor were analyzed. Both low pi, which is compatible with low leaf water potential, and high epsilon, which permits large adjustment of leaf water potential with small changes in leaf water content, may facilitate water uptake from drying soil. Leaf elastic modulus was independent of T and was weakly related to LMA; but there were close positive associations of epsilon with D and leaf dry to fresh mass ratio, which is an estimate of apoplastic leaf fraction. Consequently, changes in D bring about modifications in leaf elasticity and allow tolerance of water limitations. Across all the data, epsilon and the estimates of pi were negatively related. However, given that pi varied only fourfold, but epsilon 10-fold, I conclude that osmotic adjustment of leaf water relations is inherently limited, and that elastic adjustment resulting from changes in leaf structure may be a more important and general way for plants to adapt to water-limited environments.
A process-based leaf gas exchange model for C-3 plants was developed which specifically describes the effects observed along light gradients of shifting nitrogen investment in carboxylation and bioenergetics and modified leaf thickness due to altered stacking of photosynthetic units. The model was parametrized for the late-successional, shade-tolerant deciduous species Acer saccharum Marsh. The specific activity of ribulose-1,5-bisphosphate carboxylase (Rubisco) and the maximum photosynthetic electron transport rate per unit cytochrome f (cyt f) were used as indices that vary proportionally with nitrogen investment in the capacities for carboxylation and electron transport. Rubisco and cyt f per unit leaf area are related in the model to leaf dry mass per area (M-A), leaf nitrogen content per unit leaf dry mass (N-m), and partitioning coefficients for leaf nitrogen in Rubisco (P-R) and in bioenergetics (P-B). These partitioning coefficients are estimated from characteristic response curves of photosynthesis along with information an leaf structure and composition. While P-R and P-B determine the light-saturated value of photosynthesis, the fraction of leaf nitrogen in thylakoid light-harvesting components (P-L) and the ratio of leaf chlorophyll to leaf nitrogen invested in light harvesting (C-B), which is dependent on thylakoid stoichiometry, determine the initial photosynthetic light utilization efficiency in the model. Carbon loss due to mitochondrial respiration, which also changes along light gradients, was considered to vary in proportion with carboxylation capacity. Key model parameters - N-m, P-R, P-B, P-L, C-B and stomatal sensitivity with respect to changes in net photosynthesis (Gf)- were examined as a function of M-A, which is linearly related to irradiance during growth of the leaves. The results of the analysis applied to A. saccharum indicate that P-B and P-R increase, and G(f), P-L and C-B decrease with increasing M-A. As a result of these effects of irradiance on nitrogen partitioning, the slope of the light- saturated net photosynthesis rate per unit leaf dry mass (A(max)(m)) versus N-m relationship increased with increasing growth irradiance in mid-season. Furthermore, the nitrogen partitioning coefficients as well as the slopes of A(max)(m) versus N-m were independent of season, except during development of the leaf photosynthetic apparatus. Simulations revealed that the acclimation to high light increased A(max)(m) by 40% with respect to the low light regime. However, light-saturated photosynthesis per leaf area (A(max)(a)) varied 3-fold between these habitats, suggesting that the acclimation to high light was dominated by adjustments in leaf anatomy (A(max)(a) = A(max)(m) M-A) rather than in foliar biochemistry. This differed from adaptation to low light, where the alterations in foliar biochemistry were predicted to beat least as important as anatomical modifications. Due to the light-related accumulation of photosynthetic mass per unit area, A(max)(a) depended on M-A and leaf nitrogen per unit area (N-a). However, N-a conceals the variation in both M-A and N-m (N-a = N-m M-A), and prevents clear separation of anatomical adjustments in foliage structure and biochemical modifications in foliar composition. Given the large seasonal and site nutrient availability- related variation in N-m, and the influences of growth irradiance on nitrogen partitioning, the relationship between A(max)(a) and N-a is universal neither in time nor in space and in natural canopies at mid-season is mostly driven by variability in M-A. Thus, we conclude that analyses of the effects of nitrogen investments on potential carbon acquisition should use mass-based rather than area-based expressions.
Internal conductances to CO2 transfer from the stomatal cavity to sites of carboxylation (gi) in hypostomatous sun-and shade-grown leaves of citrus, peach and Macadamia trees (Lloyd et al. 1992) were related to anatomical characteristics of mesophyll tissues. There was a consistent relationship between absorptance of photosynthetically active radiation and chlorophyll concentration (mmol m−2) for all leaves, including sclerophyllous Macadamia, whose transmittance was high despite its relatively thick leaves. In thin peach leaves, which had high gi, the chloro-plast volume and mesophyll surface area exposed to intercellular air spaces (ias) per unit leaf area were similar to those in the thicker leaves of the evergreen species. Peach leaves, however, had the lowest leaf dry weight per area (D/a), the lowest tissue density (Td) and the highest chloro-plast surface area (Sc) exposed to ias. There were negative correlations between gi and leaf thickness or D/a, but positive correlations between gi and Sc or Sc/Td.
We developed a one-dimensional diffusion model which partitioned gi into a gaseous diffusion conductance through the ias (gias) plus a liquid-phase conductance through mesophyll cell walls (gcw). The model accounted for a significant amount of variation (r2=0.80) in measured gi by incorporating both components. The gias component was related to the one-dimensional path-length for diffusion across the mesophyll and so was greater in thinner peach leaves than in leaves of evergreen species. The gcw component was related to tissue density and to the degree of chloroplast exposure to the ias. Thus the negative correlations between gi and leaf thickness or D/a related to gias whereas positive correlations between gi and Sc or Sc/Td, related to gcw. The gcw was consistently lower than gias, and thus represented a greater constraint on CO2 diffusion in the mesophylls of these hypostomatous species.
Changes in mesophyll anatomy, gas exchange, and the amounts of nitrogen and cell wall constituents including cellulose, hemicellulose and lignin during leaf development were studied in an evergreen broad-leaved tree, Quercus glauca, and in an annual herb, Phaseolus vulgaris. The number of chloroplasts per whole leaf in P. vulgaris increased and attained the maximal level around 10 d before full leaf area expansion (FLE), whereas it continued to increase even after FLE in Q. glauca. The increase in the number of palisade tissue cells per whole leaf continued until a few days before FLE in Q. glauca, but it had almost ceased by 10 d before FLE in P. vulgaris. The radius and height of palisade tissue cells in Q. glauca, attained their maximal levels at around FLE whereas the thickness of the mesophyll cell wall and concentrations of the cell wall constituents increased markedly after FLE. These results clearly indicated that, in Q. glauca, chloroplast development proceeded in parallel with the cell wall thickening well after completion of the mesophyll cell division and cell enlargement. The sink–source transition, defined to be the time when the increase in daily carbon exchange rate exceeds the daily increase in leaf carbon content, occurred before FLE in P. vulgaris but after FLE in Q. glauca. During leaf area expansion, the maximum daily increase in nitrogen content on a whole leaf basis (the maximum leaf areas were corrected to be identical for these species) in Q. glauca was similar to that in P. vulgaris. In Q. glauca, however, more than 70% of nitrogen in the mature leaf was invested during its sink phase, whereas in P. vulgaris it was 50%. These results suggest that Q. glauca invests nitrogen for cell division for a considerable period and for chloroplast development during the later stages. We conclude that the competition for nitrogen between cell division and chloroplast development in the area of expanding leaves can explain different greening patterns among plant species.
To study the incorporation of carbon and nitrogen in different plant fractions, 3-year-old-beech (Fagus sylvatica L.) seedlings were exposed in microcosms to a dual-labelling experiment employing 13C and 15N throughout one season. Leaves, stems, coarse and fine roots were harvested 6, 12 and 18 weeks after bud break (June to September) and used to isolate acid-detergent fibre lignins (ADF lignin) for the determination of carbon and nitrogen and their isotope ratios. Lignin concentrations were also determined with the thioglycolic acid method. The highest lignin concentrations were found in fine roots. ADF lignins of all tissues analysed, especially those of leaves, also contained significant concentrations of nitrogen. This suggests that lignin-bound proteins constitute an important cell wall fraction and shows that the ADF method is not suitable to determine genuine lignin. ADF lignin should be re-named as ligno-protein fraction. Whole-leaf biomass was composed of 50 to 70% newly assimilated carbon and about 7% newly assimilated nitrogen; net changes in the isotope ratios were not observed during the experimental period. In the other tissues analysed, the fraction of new carbon and nitrogen was initially low and increased significantly during the time-course of the experiment, whereas the total tissue concentrations of carbon remained almost unaffected and nitrogen declined. At the end of the experiment, the whole-tissue biomass and ADF lignins of fine roots contained about 65 and 50% new carbon and about 50 and 40% new nitrogen, respectively. These results indicate that significant metabolic activity was related to the formation of structural biopolymers after leaf growth, especially below-ground and that this activity also led to a substantial binding of nitrogen to structural compounds.
Summary • Across species, leaf lifespan (LL) tends to be correlated with leaf mass per area (LMA). Previously we found that Australian perennial species from low-rainfall sites had c. 40% shorter LL at a given LMA than high-rainfall species. • Here we relate indices of leaf strength (work to shear, Wshear, and tissue toughness) to LL and LMA across the same suite of species. Wshear is the work required to cut a leaf with a blade; Wshear divided by leaf thickness gives tissue toughness. • Low- and high-rainfall species did not differ in their LL at a given Wshear, but dry-site species had lower Wshear at a given LMA, leading to the observed LL – LMA shift with rainfall. These patterns were driven by 50% lower tissue toughness in dry-site species. • The lower toughness was linked with high leaf N concentration, which is known to enhance water conservation during photosynthesis in low-rainfall species. Our results suggest that a significant cost of this strategy is reduced LL for a given investment in leaf tissue (LMA).
Summary • Average canopy needle age (ΛM) is an important plant characteristic determining canopy carbon gain potential. We developed a demographic model, suggesting that ΛM depends on needle maximum age (Λmax), but also on the production rate of foliage. We studied Λmax, shoot growth and branching in three conifers to disentangle the contrasting controls on ΛM. • Abies balsamea had a Λmax of up to 16 yr, Picea abies up to 12 yr, and Pinus sylvestris up to 6 yr. Increases in branch irradiance were associated with increases in shoot length, more frequent branching, increases in the asymmetry and peakedness of shoot length distributions, and decreases in Λmax and ΛM. Our model and experimental data suggested that higher ΛM at lower irradiance resulted both from increases in Λmax and decreases in branching and extension growth in the shaded branches. • Significance of various determinants of ΛM was species-dependent, and varied with needle survivorship curves and shoot bifurcation ratio. • Our study demonstrates that total foliar area and average age may be more strongly associated with branching frequency than with leaf longevity.
The profile of photosynthetic rate with depth through a leaf depends on the profiles of light absorption and photosynthetic capacity. Using a combination of several techniques, a comprehensive description of spinach leaves has been obtained. Profiles of CO2 fixation were obtained by exposing leaves to 14CO2 for 10 s under blue or green light before freeze clamping and paradermal sectioning. Profiles of light absorption were measured on adjacent parts of the leaf by quantifying chlorophyll fluorescence images of the transversely cut face obtained when blue or green light was applied to the adaxial or abaxial surface. The profile of CO2 fixation was modelled using the measured profiles of light absorption and photosynthetic capacity. There was remarkably good agreement between the observed and modelled CO2 fixation profiles for the eight combinations of colour, orientation and irradiance tested. Gas exchange of an intact leaf was also measured concurrently with conventional chlorophyll fluorescence under blue or green light. These data were consistent with the multi-layer leaf model with the exception of blue light applied to the abaxial surface, where chlorophyll fluorescence appeared to come from layers deeper than expected. Photosynthetic capacity matched the profile of green but not white light absorption through the leaf.
In this study it has been shown that increased diffusional resistances caused by salt stress may be fully overcome by exposing attached leaves to very low [CO2] (∼ 50 µmol mol−1), and, thus a non-destructive-in vivo method to correctly estimate photosynthetic capacity in stressed plants is reported. Diffusional (i.e. stomatal conductance, gs, and mesophyll conductance to CO2, gm) and biochemical limitations to photosynthesis (A) were measured in two 1-year-old Greek olive cultivars (Chalkidikis and Kerkiras) subjected to salt stress by adding 200 mm NaCl to the irrigation water. Two sets of A–Ci curves were measured. A first set of standard A–Ci curves (i.e. without pre-conditioning plants at low [CO2]), were generated for salt-stressed plants. A second set of A–Ci curves were measured, on both control and salt-stressed plants, after pre-conditioning leaves at [CO2] of ∼ 50 µmol mol−1 for about 1.5 h to force stomatal opening. This forced stomata to be wide open, and gs increased to similar values in control and salt-stressed plants of both cultivars. After gs had approached the maximum value, the A–Ci response was again measured. The analysis of the photosynthetic capacity of the salt-stressed plants based on the standard A–Ci curves, showed low values of the Jmax (maximum rate of electron transport) to Vcmax (RuBP-saturated rate of Rubisco) ratio (1.06), that would implicate a reduced rate of RuBP regeneration, and, thus, a metabolic impairment. However, the analysis of the A–Ci curves made on pre-conditioned leaves, showed that the estimates of the photosynthetic capacity parameters were much higher than in the standard A–Ci responses. Moreover, these values were similar in magnitude to the average values reported by Wullschleger (Journal of Experimental Botany 44, 907–920, 1993) in a survey of 109 C3 species. These findings clearly indicates that: (1) salt stress did affect gs and gm but not the biochemical capacity to assimilate CO2 and therefore, in these conditions, the sum of the diffusional resistances set the limit to photosynthesis rates; (2) there was a linear relationship (r2 = 0.68) between gm and gs, and, thus, changes of gm can be as fast as those of gs; (3) the estimates of photosynthetic capacity based on A–Ci curves made without removing diffusional limitations are artificially low and lead to incorrect interpretations of the actual limitations of photosynthesis; and (4) the analysis of the photosynthetic properties in terms of stomatal and non-stomatal limitations should be replaced by the analysis of diffusional and non-diffusional limitations of photosynthesis. Finally, the C3 photosynthesis model parameterization using in vitro-measured and in vivo-measured kinetics parameters was compared. Applying the in vivo-measured Rubisco kinetics parameters resulted in a better parameterization of the photosynthesis model.
1. The influence of leaf thickness on internal conductance for CO 2 transfer from substomatal cavity to chloroplast stroma ( g i ) and carbon isotope ratio (δ ¹³ C) of leaf dry matter was investigated for some evergreen tree species from Japanese temperate forests. g i was estimated based on the combined measurements of gas exchange and concurrent carbon isotope discrimination.
2. Leaves with thicker mesophyll tended to have larger leaf dry mass per area (LMA), larger surface area of mesophyll cells exposed to intercellular air spaces per unit leaf area ( S mes ) and smaller volume ratio of intercellular spaces to the whole mesophyll (mesophyll porosity).
3. g i of these leaves was correlated positively to S mes but negatively to mesophyll porosity. The variation in g i among these species would be therefore primarily determined by variation of the conductance in liquid phase rather than that in gas phase.
4. δ ¹³ C was positively correlated to mesophyll thickness and leaf nitrogen content on an area basis. However, g i values did not correlate to δ ¹³ C. These results suggest that difference in δ ¹³ C among the species was not caused by the variation in g i , but mainly by the difference in long‐term photosynthetic capacity.
5. Comparison of our results with those of previous studies showed that the correlation between leaf thickness and g i differed depending on leaf functional types (evergreen, deciduous or annual). Differences in leaf properties among these functional types were discussed.
1. Changes of δ13C and its relation to leaf development, biochemical content and water stress were monitored over a 2 year period in two co-occurring Mediterranean oak species: the deciduous Quercus pubescens and the evergreen Quercus ilex.
2. The time course of leaf δ13C showed different patterns in the two species. Young Q. pubescens leaves had a high δ13C and a marked decrease occurred during leaf growth. In contrast, leaves at budburst and maturity did not differ significantly in the case of Q. ilex. We suggest that the difference between δ13C of young leaves was linked to differential use of reserves of carbon compounds in the two species.
3.δ13C values of mature leaves were negatively correlated with minimum seasonal values of predawn water potential, suggesting that a functional adjustment to water resources occurred.
4. There was a significant correlation between individual δ13C values for two successive years. This interannual dependence showed that δ13C rankings between trees were constant through time.
Olive (Olea europea L) is one of the most valuable and widespread fruit trees in the Mediterranean area. To breed olive for resistance to salinity, an environmental constraint typical of the Mediterranean, is an important goal. The photosynthetic limitations associated with salt stress caused by irrigation with saline (200 mm) water were assessed with simultaneous gas-exchange and fluorescence field measurements in six olive cultivars. Cultivars were found to possess inherently different photosynthesis when non-stressed. When exposed to salt stress, cultivars with inherently high photosynthesis showed the highest photosynthetic reductions. There was no relationship between salt accumulation and photosynthesis reduction in either young or old leaves. Thus photosynthetic sensitivity to salt did not depend on salt exclusion or compartmentalization in the old leaves of the olive cultivars investigated. Salt reduced the photochemical efficiency, but this reduction was also not associated with photosynthesis reduction. Salt caused a reduction of stomatal and mesophyll conductance, especially in cultivars with inherently high photosynthesis. Mesophyll conductance was generally strongly associated with photosynthesis, but not in salt-stressed leaves with a mesophyll conductance higher than 50 mmol m−2 s−1. The combined reduction of stomatal and mesophyll conductances in salt-stressed leaves increased the CO2 draw-down between ambient air and the chloroplasts. The CO2 draw-down was strongly associated with photosynthesis reduction of salt-stressed leaves but also with the variable photosynthesis of controls. The relationship between photosynthesis and CO2 draw-down remained unchanged in most of the cultivars, suggesting no or small changes in Rubisco activity of salt-stressed leaves. The present results indicate that the low chloroplast CO2 concentration set by both low stomatal and mesophyll conductances were the main limitations of photosynthesis in salt-stressed olive as well as in cultivars with inherently low photosynthesis. It is consequently suggested that, independently of the apparent sensitivity of photosynthesis to salt, this effect may be relieved if conductances to CO2 diffusion are restored.
The internal conductance from intercellular spaces to the sites of carboxylation (gi) has only been measured in a few tree species and not in conifers, despite the fact it may impose a large limitation on photosynthesis. The present study provides the first estimates of gi for a coniferous species, and examines variation in gi with height and its relationships to anatomical, biochemical and physiological traits. Measurements were made on upper and lower canopy current-year needles of 50-year-old Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco). Needle thickness and specific leaf area decreased by 30% from the top to bottom of the canopy. These anatomical/morphological changes were accompanied by modest variation in allocation of N to chlorophyll and the chlorophyll a/b ratio. Allocation of N to Rubisco did not vary with height, but the ratio of Rubisco to chlorophyll did owing to the aforementioned changes in allocation to chlorophyll. The value of gi was estimated in one tree from concurrent measurements of carbon isotope discrimination and net photosynthesis. To examine the variation in gi among trees a second independent method based on day respiration and the difference between the chloroplastic and intercellular photocompensation points (photocompensation point method) was used. Estimates of gi obtained by the two methods agreed well with values varying between 0.14 and 0.20 mol m−2 s−1. It is estimated that gi limits photosynthesis by approximately 20% as compared to an approximately 30% stomatal limitation (under well-watered conditions). The value of gi scaled approximately with maximum rates of photosynthesis, which were significantly greater in upper canopy needles. Nevertheless, gi did not vary significantly with canopy height, owing to greater variability in gi than photosynthesis.
A phenomorphological survey was carried out in central Italy to study the effects of increasing water stress on some characteristic species of the Mediterranean maquis. Nutrient content and leaf water potential were examined. The results show that three different groups exist which diverge in the modulation of growth activity. 1) Evergreen sclerophyllous species (e.g. Pistacia lentiscus, Phillyrea media, Arbutus unedo, Ruscus aculeatus), which were supposed to be drought-tolerant, in fact limited their growth activity to a brief period before aridity increased. A similar growth pattern was exhibited by those species (e.g. Quercus ilex, Erica arborea, Smilax aspera) that stopped producing new leaves and branches during the driest season and that recovered after the first rain; i.e., their growth period lasted longer. 2) Drought-deciduous species (e.g. Calicotome villosa) that adopted the drought-avoidance strategy had two vegetative periods interrupted by a phase during which they completely shed their leaves. 3) Semideciduous species (Cistus monspeliensis) with mesophitic leaves adopted an intermediate response. These grew even in the dry and cold season.
The effect of clearcutting on biomass production and nutrient consumption was examined during the two years in a clearcut and a mature Quercus ilex L. coppice. The comparison was limited to the leaf compartment and to the annual shoots, which were the only comparable compartments in the two situations. At the same time, the dynamics of the nutrient pool (N, P, K, Ca, Mg), monthly uptake and recycling from the foliage, were studied.
The second year after cutting, the leaf production was roughly the same at the two sites. However, the photosynthates appear to be used differently: in the young stand the perennial wood production was greater than in the mature stand, where the maintenance costs are higher. This is corroborated by the patterns of nutrient use.
Simulations using a biochemically-based model of leaf photosynthesis make it possible to predict the distribution of leaf nitrogen contents that maximizes photosynthetic carbon gain over the canopy of an entire plant. In general, the optimal nitrogen content increased with increasing daily photosynthetically active photon irradiance. Leaf aging in natural environments tended to produce leaf nitrogen contents that were similar to the optimal values but somewhat more clustered. Nitrogen redistribution over the duration of a leaf involves costs that are smaller than the benefits in increased photosynthesis. The costs could become larger than the benefits if nitrogen were redistributed on a shorter time scale.
A mechanistically based C3 leaf photosynthesis model combined with an empirical stomatal model and a canopy model of light interception and microclimate was used to simulate Quercus ilex canopy net photosynthesis and transpiration at l'Avic watershed (NE Spain). The model takes into account the sun-shade leaf differentiation of photosynthetic characteristics as affected by depth within the canopy. Based on field studies, simulations were carried out for two locations within the watershed along a gradient in elevation, microclimate and forest structure. Effective predictions of diurnal and seasonal courses of stomatal conductance of sun and shade leaves for different days during the year were obtained by changing a single model variable termed gF. The value of gF determined from least squares of observed vs. simulated time courses was linearly related to pre-dawn xylem water potential over critical ranges of the response curve. Response to gF in the model may to a great extent be thought of as the integrated expression of canopy response to root system generated signals or control mechanisms. For development of predictive capability, gF is extremely useful because it allows seasonal assessments of water use and carbon dioxide uptake with differing patterns in water availability. Based on simulated responses on representative clear, overcast and variable days throughout the year, only small differences in annual totals for net photosynthesis and transpiration were found between the two sites, despite large differences in soil drying. Annual estimates of canopy water loss were in close agreement with independent estimates of evapotranspiration using the hydrological input/output method.
The transpiration of oak-savannas in southern Spain was modelled by scaling-up from the leaf to the tree during a drought period. Two characteristics of this ecosystem were found to facilitate the modelling procedure. The first was a near-zero decoupling coefficient between the surface and the surrounding bulk air, which simplifies the transpiration formulation. The second was that the surface conductance (g) is mainly related to the vapour pressure deficit of the air (Da). Based on both of these characteristics, the modelling procedure provides a general model of transpiration over the time scale appropriate for a drought period, from days to months. The response of g to Da was found to follow a negative exponential function, such that beyond a minimum value, g becomes independent of Da. This implies a feedback control on g by Da. The consequences of this control for transpiration were found at different levels of plant water status. This explains the plants' adaptation to long dry periods, even though there is also continuous water loss during these periods. Such an adaptation was corroborated by a seasonal hysteresis found in the relationship between transpiration and Da as a function of the plants' water status.
1 Outdoor microcosms were used to investigate the effects of invertebrate herbivory on plant community composition, and thereby infer possible effects on the rate of secondary succession, at differing levels of soil fertility.
2 A mixture containing 24 grassland plant species of widely different functional types was established, with 12 microcosms at each of three fertility levels. Four generalist herbivores (Helix aspersa, Cepaea hortensis, Arianta arbustorum and Sitobion avenae) were added to half of the microcosms. Above-ground biomass of each species was harvested after 2 years. Reproductive variables were also measured for one species, Poa annua.
3 At both moderate and high soil fertility generalist invertebrate herbivores fed selectively on early successional, fast-growing species, thus increasing the relative abundance of later successional, slow-growing species. This supports the hypothesis that herbivory increases the rate of secondary succession. Flowering and viable seed production of early successional ephemerals was also reduced by the invertebrate herbivores across a wide range of soil fertility. This would seriously reduce the ability of a species to persist in the community, thereby further hastening the rate of succession.
Drought control over conductance and assimilation was assessed using eddy flux and meteorological data monitored during four summer periods from 1998 to 2001 above a closed canopy of the Mediterranean evergreen oak tree Quercus ilex. Additional discrete measurements of soil water content and predawn leaf water potential were used to characterize the severity of the drought.
Canopy conductance was estimated through the big-leaf approach of Penman–Monteith by inverting latent heat fluxes. The gross primary production (GPP) was estimated by adding ecosystem respiration to net ecosystem exchange. Ecosystem respiration was deduced from night flux when friction velocity (u*) was greater than 0.35 m s−1. Empirical equations were identified that related maximal canopy conductance and daily ecosystem GPP to relative soil water content (RWC), the ratio of current soil water content to the field capacity, and to the predawn leaf water potential. Both variables showed a strong decline with soil RWC for values lower than 0.7. The sharpest decline was observed for GPP. The curves reached zero for RWC=0.41 and 0.45 for conductance and GPP, respectively. When the predawn leaf water potential was used as a surrogate for soil water potential, both variables showed a hyperbolic decline with decreasing water potential.
These results were compared with already published literature values obtained at leaf level from the same tree species. Scaling up from the leaf to ecosystem highlighted the limitation of two big-leaf representations: Penman–Monteith and Sellers' Π factor. Neither held completely for comparing leaf and canopy fluxes. Tower measurements integrate fluxes from foliage elements clumped at several levels of organization: branch, tree, and ecosystem. The Q. ilex canopy exhibited non-random distribution of foliage, emphasizing the need to take into account a clumping index, the factor necessary to apply the Lambert–Beer law to natural forests.
Our results showed that drought is an important determinant in water losses and CO2 fluxes in water-limited ecosystems. In spite of the limitations inherent to the big-leaf representation of the canopy, the equations are useful for predicting the influence of environmental factors in Mediterranean woodlands and for interpreting ecosystem exchange measurements.
Drought is one of the most important limitations in Mediterranean climates. However, Mediterranean sclerophyllous species with long-lived leaves also support extensive and dynamic canopies, with potentially large spatial and age-dependent gradients. We studied within-canopy and temporal patterns in foliage structure, chemistry and and photosynthesis in the evergreen species Quercus coccifera L., Q.ilex L. subsp. ballota (Desf.) Samp in Bol. and Q.suber L. and in the semi-deciduous marcescent species Q.faginea Lam. to determine the role of within canopy shadingand leaf age on foliage functioning. There was a 2.5-fold within canopy gradient in leaf dry mass per unit area (MA) that was accompanied by a 3-fold range area-based leaf nitrogen (N) content, the capacity for photosynthetic electron transport (JMAX) and maximum Rubisco carboxylase activity (VCMAX), while the fractional investments of leaf nitrogen in elect ron transport (FB) and in Rubisco (FR) were relatively constant within the canopy. Leaf aging led to increase MA, larger or constant mass-based N content, larger phosphorus (P) and structural carbon contents, but decreased movable cation contents. Age-dependent increases in MA and N per dry mass meant that JMAX and VCMAX per area were weakly related to leaf age, with a trend of decreasing values in older leaves. Hwever, JMAX and VCMAX per unit dry mass decreased 4-fold across the range of leaf age, primarily owing to
Gas exchange measurements were carried out on ash and oak trees in a forest plantation during three whole growing seasons characterized by different water availability (2001, 2002 and 2003). A quantitative limitation analysis was applied to estimate the effects of drought and leaf ontogeny on stomatal (SL) and non-stomatal limitations (NSL) to light-saturated net photosynthesis (Amax), relative to the seasonal maximum rates obtained under conditions of optimal soil water content. Furthermore, based on combined gas exchange and chlorophyll fluorescence measurements, NSL was partitioned into a diffusive (due to a decrease in mesophyll conductance, MCL) and a biochemical component (due to a decrease in carboxylation capacity, BL). During the wettest year (2002), the seasonal pattern of both Amax and stomatal conductance (gsw) was characterized in both species by a rapid increase during spring and a slight decline over the summer. However, with a moderate (year 2001) or a severe (year 2003) water stress, the summer decline of Amax and gsw was more pronounced and increased with drought intensity (30–40% in 2001, 60–75% in 2003). The limitation analysis showed that during the spring and the autumn periods SL, MCL and BL were of similar magnitude. By contrast, from the summer data it emerged that all the limitations increased with drought intensity, but their relative contribution changed. At mild to moderate water stress (corresponding to values of gsw > 100 mmol H2O m-2 s-1) about two-thirds of the decline in Amax was attributable to SL. However, with increasing drought intensity, NSL increased more than SL and nearly equalled it when the stress was very severe (i.e. with gsw < 60 mmol H2O m-2 s-1). Within NSL, MCL represented the main component, except at the most severe water stress levels when it was equalled by BL. It is concluded that diffusional limitations (i.e. SL + MCL) largely affect net assimilation during most of the year, whereas biochemical limitations are quantitatively important only during leaf development and senescence or with severe droughts.
Virtually all current estimates of the maximum carboxylation rate (Vcmax) of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) and the maximum electron transportrate (Jmax) for C3 species implicitly assume an infinite CO2 transfer conductance (gi). And yet, most measurements in perennial plant species or in ageing or stressed leaves show that gi imposes a significant limitation on photosynthesis. Herein, we demonstrate that many current parameterizations of the photosynthesis model of Farquhar, von Caemmerer & Berry (Planta 149, 78–90, 1980) based on the leaf intercellular CO2 concentration (Ci) are incorrect for leaves where gi limits photosynthesis. We show how conventional A–Ci curve (net CO2 assimilation rate of a leaf – An – as a function of Ci ) fitting methods which rely on a rectangular hyperbola model under the assumption of infinite gi can significantly underestimate Vcmax for such leaves. Alternative parameterizations of the conventional method based on a single, apparent Michaelis–Menten constant for CO2 evaluated at Ci [Km(CO2)i] used for all C3 plants are also not acceptable since the relationship between Vcmax and gi is not conserved among species. We present an alternative A–Ci curve fitting method that accounts for gi through a non-rectangular hyperbola version of the model of Farquhar et al. (1980). Simulated and real examples are used to demonstrate how this new approach eliminates the errors of the conventional A–Ci curve fitting method and provides Vcmax estimates that are virtually insensitive to gi. Finally, we show how the new A–Ci curve fitting method can be used to estimate the value of the kinetic constants of Rubisco in vivo is presented
Predicting the environmental responses of leaf photosynthesis is central to many models of changes in the future global carbon cycle and terrestrial biosphere. The steady state biochemical model of C3 photosynthesis of Farquhar et al. (Planta 149, 78–90, 1980) provides a basis for these larger scale predictions; but a weakness in the application of the model as currently parameterized is the inability to accurately predict carbon assimilation at the range of temperatures over which significant photosynthesis occurs in the natural environment. The temperature functions used in this model have been based on in vitro measurements made over a limited temperature range and require several assumptions of in vivo conditions. Since photosynthetic rates are often Rubisco-limited (ribulose, 1-5 bisphosphate carboxylase/oxygenase) under natural steady-state conditions, inaccuracies in the functions predicting Rubisco kinetic properties at different temperatures may cause significant error. In this study, transgenic tobacco containing only 10% normal levels of Rubisco were used to measure Rubisco-limited photosynthesis over a large range of CO2 concentrations. From the responses of the rate of CO2 assimilation at a wide range of temperatures, and CO2 and O2 concentrations, the temperature functions of Rubisco kinetic properties were estimated in vivo. These differed substantially from previously published functions. These new functions were then used to predict photosynthesis in lemon and found to faithfully mimic the observed pattern of temperature response. There was also a close correspondence with published C3 photosynthesis temperature responses. The results represent an improved ability to model leaf photosynthesis over a wide range of temperatures (10–40 °C) necessary for predicting carbon uptake by terrestrial C3 systems.
The process-based simulation model STANDFLUX describes canopy water vapor and carbon dioxide exchange based on rates calculated for individual trees and as affected by local gradients in photon flux density (PFD), atmospheric humidity, atmospheric carbon dioxide concentration, and air temperature. Direct, diffuse, and reflected PFD incident on foliage elements within compartments of individual trees (defined by vertical layers and a series of concentric cylinders centered on the trunk) is calculated for a 3-dimensional matrix of points. Foliage element gas exchange rates are based on estimates of carboxylation, RuBP regeneration, and respiratory capacities as well as the correlated behavior found between stomatal conductance and assimilation rate. Because of the difficulties associated with effective sampling and description of spatial variation in structure and leaf level gas exchange parameters for trees comprising the forest canopy, the significance for canopy water and carbon dioxide exchange of varied representations of tree foliage distribution and of physiology is examined. The additional interactive effects encountered due to changes in tree density and, thus, spatial aggregation or disaggregation of foliage is also studied. The analysis is conducted within the context of observed structural and physiological variation encountered in Norway spruce (Picea abies) stands in the Fichtelgebirge region of central Germany. Potentials for simplifying the three-dimensional canopy gas exchange model without sizable influence on canopy flux rates were small. A relatively large number of sample points within the tree crowns is necessary to obtain consistent calculations of flux rates because of the non-linear relationship between PFD and net photosynthesis. Transpiration and net photosynthesis for stands with a low leaf area index (LAI) may be obtained from single tree estimates for each tree class weighted by class frequency, while 30 or more trees per class in differing relation to neighboring trees may be necessary to calculate reliable estimates of net photosynthesis in canopies with high LAI. The complexity in structure assumed for modeled trees was important, especially when overall canopy foliage area was either high or low due to spatial heterogeneity in clumping, e. g., potential canopy overlaps or side-lighting. Effects were greater for calculated net photosynthesis than for transpiration, reflecting higher sensitivity of net photosynthesis to differences in light distribution within individual trees. Accuracy in estimates of physiological parameters is equally important, and these characteristics have profound effects on estimated canopy gas exchange rates. While one-dimensional representations of canopy structure or approximations of tree physiological characteristics from other canopies or species may often be necessary in assessing vegetation/atmosphere exchanges, especially in the study of water balance of landscapes or regions, STANDFLUX provides a tool that can aid in evaluating the limitations of these simpler approaches.
Changes in needle morphology, average needle age, shoot length growth, and branching frequency in response to seasonal average integrated quantum flux density ($Q_{\textrm{int}}$) were investigated in Pinus sylvestris L. in a fertile site (old-field) and an infertile site (raised bog). In the fertile site, the trees were 30 years old with a dominant height of 17–21 m, and with average $\pm$ SD nitrogen content (% of dry mass) of 1.53 $\pm$ 0.11 in the current-year needles. In the infertile site, 50 to 100-yr-old trees were 1–2 m tall, and needle N content was 0.86 $\pm$ 0.12%. Relationships between the variables were studied using linear correlation and regression analyses. With increasing irradiance, shoot length ($L_{\textrm{s}}$) and shoot bifurcation ratio ($R_{\textrm{b}}$, the number of current-year shoots per number of shoots formed in the previous year) increased in the fertile site, but not in the infertile site. Despite greater branching frequency, apical control was enhanced at higher irradiance in the fertile site. The shoot length distributions became more peaked (positive kurtosis) and biased towards lower values of $L_{\textrm{s}}$ (positive skewness) with increasing $Q_{\textrm{int}}$ in this stand. The shoot distributions were essentially normal in the infertile site. Large values of $R_{\textrm{b}}$ combined with the skewed distributions of shoot length resulted in conical crowns in the fertile site. In contrast, lower bifurcation ratio, normal shoot length distributions and low rates of shoot length growth led to flat-topped crowns in the bog. Average needle age was independent of $Q_{\textrm{int}}$, but was larger in the infertile site. Thus, reduced rates of foliage production in the infertile site were somewhat compensated for by increased foliage longevity, and we suggest that shoot growth rates may have directly controlled the needle life span via reduced requirements for nutrients for the growth and via reduced self-shading within the canopy. Needle age and $Q_{\textrm{int}}$ independently affected needle structure. Needle age only moderately altered needle nutrient contents, but the primary age-related modification was the scaling of needle density with age. The density was similarly modified by age in both sites, but the needles were denser in the infertile site. Given that denser needles are more resistant to mechanical injury, larger density may provide an additional explanation for enhanced longevity in the infertile site. Our study demonstrates that site fertility is an important determinant of the plastic modifications in crown geometry, and needle life span in P. sylvestris. Longévité des aiguilles, croissance des pousses et fréquence de ramification en relation avec la fertilité du site et les conditions de lumière dans la canopée de Pinus sylvestris. Les changements dans la morphologie des aiguilles, l'âge moyen des aiguilles, la croissance en longueur des pousses, la fréquence de la ramification ont été étudiés en réponse à la densité du flux quantique intégré ($Q_{\textrm{int}}$) moyen saisonnier chez Pinus sylvestris L. dans un site fertile (anciennement cultivé) et dans un site pauvre (tourbière). Dans le site fertile, les arbres étaient âgés de 30 ans, avec une hauteur dominante de 17–21 m, et une teneur en azote (g kg$^{-1}$ de matière sèche) moyenne de 15,3 $\pm$ 1,1 dans les aiguilles de l'année. Dans le site pauvre, les arbres, âgés de 50 à 100 ans, avaient une taille de 1 à 2 m, la teneur en azote des aiguilles était de 8,6 $\pm$ 1,2 g kg$^{-1}$. Les relations entre les variables ont été étudiées en utilisant les analyses de corrélation linéaire et de régression. Lorsque l'irradition est croissante, la longueur de la pousse ($L_{\textrm{s}}$) et le rapport de ramification ($R_{\textrm{b}}$, nombre de pousses de l'année par nombre de pousse formées au cours de l'année précédente) augmentent dans le site fertile, mais pas dans le site pauvre. Malgré une fréquence plus élevée de ramification, le contrôle apical est exacerbé par une irradiation plus élevée dans le site fertile. Les distributions des longueurs de pousse deviennent plus pointues (kurtosis positive) et biaisées vers les valeurs les plus faibles de $L_{\textrm{s}}$ (skewness positive) avec un $Q_{\textrm{int}}$ en augmentation dans ce site. Les fortes valeurs de $R_{\textrm{b}}$, combinées avec des distributions skewness des longueurs de pousses conduisent à des canopées coniques dans le site fertile. Par opposition, un rapport plus faible de la ramification, distributions normales des longueurs de pousses, et une faible croissance en longueur des pousses conduisent à la formation de canopées aplaties dans la tourbière. L'âge moyen des aiguilles était indépendant du $Q_{\textrm{int}}$, mais il était plus élevé dans le site le plus pauvre. Cependant, les taux réduits de production foliaire dans la station pauvre étaient, en quelque sorte, compensés par l'accroissement de longévité du feuillage, et nous suggérons que les taux de croissance des pousses peuvent avoir contrôlé directement la durée de vie des aiguilles par une réduction des besoins en nutriments pour la croissance et par une réduction de l'ombre dans la canopée. L'âge des aiguilles et $Q_{\textrm{int}}$ affectent indépendamment la structure des aiguilles. L'âge des aiguilles modifie seulement modérément la teneur en nutriments des aiguilles, mais la modification primaire liée à l'âge, était l'échelle de densité d'aiguilles. La densité était pareillement modifiée par l'âge dans les deux stations, mais les aiguilles étaient plus denses dans le site pauvre. étant donné que des aiguilles plus denses sont plus résistantes aux blessures mécaniques, une plus grande densité peut fournir une explication additionnelle à la longévité renforcée dans les stations pauvres. Notre étude démontre que la fertilité de la station est un important déterminant des modifications plastiques de la géométrie de la couronne et la durée de vie des aiguilles chez P. sylvestris.