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Drought limitation of photosynthesis differs between C3 and C4 grass species in a comparative experiment
Abstract
Phylogenetic analyses show that C₄ grasses typically occupy drier habitats than their C₃ relatives, but recent experiments comparing the physiology of closely related C₃ and C₄ species have shown that advantages of C₄ photosynthesis can be lost under drought. We tested the generality of these paradoxical findings in grass species representing the known evolutionary diversity of C₄ NADP-me and C₃ photosynthetic types. Our experiment investigated the effects of drought on leaf photosynthesis, water potential, nitrogen, chlorophyll content and mortality. C₄ grasses in control treatments were characterized by higher CO₂ assimilation rates and water potential, but lower stomatal conductance and nitrogen content. Under drought, stomatal conductance declined more dramatically in C₃ than C₄ species, and photosynthetic water-use and nitrogen-use efficiency advantages held by C₄ species under control conditions were each diminished by 40%. Leaf mortality was slightly higher in C₄ than C₃ grasses, but leaf condition under drought otherwise showed no dependence on photosynthetic-type. This phylogenetically controlled experiment suggested that a drought-induced reduction in the photosynthetic performance advantages of C₄ NADP-me relative to C₃ grasses is a general phenomenon.
... For example, maize plants have C 4 photosynthetic pathway, while soybean are classified as C 3 , being less efficient under warm temperatures as their photorespiration is higher [21,22]. Soil water stress could lead to more substantial declines of g s in C 3 species than C 4 , due to metabolic limitations [23,24]. In addition, species with more anisohydric behavior, as reported for maize [25] can delay stomatal closure, maintaining photosynthesis level. ...
... However, if reductions in g s are linked to reductions in Ψ L as shown by Wijewardana et al. (2019) [17], it could be inferred that soybean plants behaved more as isohydric crop compared to our type of maize plants. This could also be associated with the type of photosynthetic pathway as C 3 species such as soybean tend to exhibit more considerable reductions in g s than their C 4 relatives under drought [23]. Nevertheless, according to Costa et al. (2013) [48], g s is better indicator of soil water stress in isohydric plants, enabling thermal imaging to better detect drought, as we observed in our results ( Figure 6). ...
... Thus, the models might not detect high signals in water bands. According to Taylor et al. (2011) [23], in C 4 species, drought effects in A and T r might be more visible in the whole plant rather in specific leaf compared with C 3 plants. ...
During water stress, crops undertake adjustments in functional, structural, and biochemical traits. Hyperspectral data and machine learning techniques (PLS-R) can be used to assess water stress responses in plant physiology. In this study, we investigated the potential of hyperspectral optical (VNIR) measurements supplemented with thermal remote sensing and canopy height (h c) to detect changes in leaf physiology of soybean (C 3) and maize (C 4) plants under three levels of soil moisture in controlled environmental conditions. We measured canopy evapotranspiration (ET), leaf transpiration (T r), leaf stomatal conductance (g s), leaf photosynthesis (A), leaf chlorophyll content and morphological properties (h c and LAI), as well as vegetation cover reflectance and radiometric temperature (T L,Rad). Our results showed that water stress caused significant ET decreases in both crops. This reduction was linked to tighter stomatal control for soybean plants, whereas LAI changes were the primary control on maize ET. Spectral vegetation indices (VIs) and T L,Rad were able to track these different responses to drought, but only after controlling for confounding changes in phenology. PLS-R modeling of g s , T r , and A using hyperspectral data was more accurate when pooling data from both crops together rather than individually. Nonetheless, separated PLS-R crop models are useful to identify the most relevant variables in each crop such as T L,Rad for soybean and h c for maize under our experimental conditions. Interestingly, the most important spectral bands sensitive to drought, derived from PLS-R analysis, were not exactly centered at the same wavelengths of the studied VIs sensitive to drought, highlighting the benefit of having contiguous narrow spectral bands to predict leaf physiology and suggesting different wavelength combinations based on crop type. Our results are only a first but a promising step towards larger scale remote sensing applications (e.g., airborne and satellite). PLS-R estimates of leaf physiology could help to parameterize canopy level GPP or ET models and to identify different photosynthetic paths or the degree of stomatal closure in response to drought.
... C 3 and C 4 plants are two differential functional types that respond differently to environmental stress due to contrasting water-carbon balance. C 4 photosynthesis refers to various modifications in anatomy, biochemistry, and physiology that strategically concentrate CO 2 in the bundle sheath, which leads to the saturation of Rubisco at ambient CO 2 concentrations (Sage and Pearcy, 1987;Taylor et al., 2011;Osborne and Sack, 2012;Taylor et al., 2014). C 4 plants are able to increase their maximum net photosynthesis rates with less stomatal conductance compared to C 3 species by almost eliminating photorespiration. ...
... Such a strategy seemed to be beneficial for maintaining its hydraulic functions (Zhu and Cao, 2009;Chen et al., 2015) during the dry season with high temperatures and evaporative demand. The smaller stomatal aperture and higher efficiency of water use in H. ammodendron were consistent with the typical pattern and classical understanding of the traits of C 4 grass species discussed in previous reports and developed models (Kocacinar and Sage, 2003;Taylor et al., 2011;Osborne and Sack, 2012;Taylor et al., 2014). This is also the case for the Central Asian C 4 shrub based on the present study. ...
Resources in water-limited ecosystems are highly variable and unpredictable, and the maintenance of functional diversity among coexisting species is a crucial ecological strategy through which plants mitigate environmental stress. The comparison of differential eco-physiological responses among co-occurring plants in harsh environments could help provide deep insights into the coexistence mechanisms of competing species. Two coexisting desert shrubs with different photosynthetic pathways (Haloxylon ammodendron and Tamarix ramosissima) were selected in the Gurbantunggut Desert located in northwest China. This study detected variations in the water sources, photosynthetic parameters, stem water status, and non-structural carbohydrates of the two shrubs at three sites with different groundwater table depths during the growing seasons of 2015 and 2016 to identify distinct eco-physiological performances in coexisting plants with different functional types under fluctuating water conditions. The water sources of H. ammodendron shifted from soil water to groundwater, while T. ramosissima extracted water mainly from deep soil layers at both sites. Significant reductions in carbon assimilation and stomatal conductance in H. ammodendron with deeper groundwater table depth were detected during most drought periods, but no significant decreases in transpiration rate were detected with declining groundwater table depth. For T. ramosissima, all of these gas exchange parameters decreased with the progression of summer drought, and their relative reduction rates were larger compared with those of H. ammodendron. The stem water status of H. ammodendron deteriorated, and the relative reduction rates of water potential increased with deeper groundwater, whereas those of T. ramosissima did not differ with greater groundwater depth. These findings indicated that prolonged drought would intensify the impact of declining groundwater depth on the eco-physiology of both shrubs, but the extent to which the shrubs would respond differed. The two shrubs were segregated along the water–carbon balance continuum: the C3 shrub T. ramosissima maximized its carbon fixation at an enormous cost of water, while greater carbon fixation was achieved with far greater water economy for H. ammodendron. These results demonstrated that the two shrubs prioritized carbon gain and water loss differently when faced with limited water sources. These mechanisms might mitigate competitive stress and enable their coexistence.
... The soil nutrients are adversely affected by varying levels of acidic conditions by restricting the ease with which they are available, resulting in nutrient deficiency in plants, and their normal physiological growth pattern is lost (Taylor et al. 2011;Tripathi et al. 2019;Li et al. 2019). The early exposure to salinity notices the ion toxicity within the cells, leading to disruption of osmotic balance if the stress persists for a more extended period. ...
... In their habitats, plants being sessile organisms continuously interact with a number of variable factors ranging from biotic to abiotic stresses. Within an ecosystem, the survival of floral diversity necessitates a number of appropriate defense mechanisms (Taylor et al. 2011;Adisa et al. 2019). Out of these, the chemical defense mechanism involves the major trait of an immune system to combat the unfavorable environment. ...
Sugarcane is grown by small, medium, and large rural farmers in several countries around the globe. In addition, the primary objective is to increase cane yield, sugar recovery and sustainably improve the livelihoods of cane farmers. For producing a large amount of biomass and sugarcane, crop extracts a large amount of nutrients from the soil and accumulate in the plant. The regular harvesting of natural resources consequently from the soil mitigates a high amount of nutrients. Therefore, there is always a need to replace these nutrients with other sources of fertilization. Soil textural properties and fertility status under changing climatic conditions also play an important role. Several alternatives can be utilized to increase the sustainable nutrient use efficiency of both macro and micronutrients to make a balance for the profitability of the crop. Two of these natural alternatives are the use of green and organic manure, i.e., press mud and farmyard manure. This chapter aims to develop an integrated nutrient management approach for the global cane farmers that would improve the quality and productivity of the canes and improve water, nutrients, and pesticide use efficiencies.
... The soil nutrients are adversely affected by varying levels of acidic conditions by restricting the ease with which they are available, resulting in nutrient deficiency in plants, and their normal physiological growth pattern is lost (Taylor et al. 2011;Tripathi et al. 2019;Li et al. 2019). The early exposure to salinity notices the ion toxicity within the cells, leading to disruption of osmotic balance if the stress persists for a more extended period. ...
... In their habitats, plants being sessile organisms continuously interact with a number of variable factors ranging from biotic to abiotic stresses. Within an ecosystem, the survival of floral diversity necessitates a number of appropriate defense mechanisms (Taylor et al. 2011;Adisa et al. 2019). Out of these, the chemical defense mechanism involves the major trait of an immune system to combat the unfavorable environment. ...
This edited volume focuses on the core aspects of sugarcane production-management under stressful environments as well as innovative strategies for augmenting crop growth & productivity through intrinsic and extrinsic manipulations. The various chapters aim at bringing out comprehensive and advance information on different aspects of sugarcane cultivation under stress environments and impact of climate change on the sustainability of sugarcane production. The book encompasses information about crop production management, physiological & nutritional requirements, ratooning, ripening and post-harvest losses management. It also delineates various technologies that support the continued use and improvement of sugarcane as renewable source of food, fiber and bio-energy. The manipulations at cellular and molecular levels, molecular breeding approaches and post-harvest technologies are also included. The area under sugarcane cultivation is gradually increasing because of its diversification potential. The high productivity and biomass of the cane crop also makes it a key source for use as bio-energy crop and a promising raw material for bio-based agro-industries. However, poor crop & biomass productivity due to abiotic stress is the foremost constraint in its future commercial exploitation as sustainable feed-stock for bio-based industries. It is therefore imperative to understand the cellular-molecular modulation responsible to productivity barrier under specific stress situation(s) for better sugarcane quality and quantum under field condition. Some of these innovative approaches are delineated in this book. This book is of interest to progressive sugarcane growers, millers, industrial entrepreneurs, sugarcane scientists, cane development and extension officers, sugar industry managers and valuable source of reference worldwide.
... Crops convert atmospheric CO 2 into SOC, thus linking the abiotic and biotic components of the carbon (C) cycle. Field crops are normally grouped into C3 and C4 categories with different photosynthetic efficiency (Taylor et al. 2015). Generally, C4 crops (e.g., maize and sorghum) have higher photosynthetic activity and CO 2 assimilation rates compared with C3 crops (e.g., wheat and rice) (Taylor et al. 2015). ...
... Field crops are normally grouped into C3 and C4 categories with different photosynthetic efficiency (Taylor et al. 2015). Generally, C4 crops (e.g., maize and sorghum) have higher photosynthetic activity and CO 2 assimilation rates compared with C3 crops (e.g., wheat and rice) (Taylor et al. 2015). The stable C isotope 13 C based on natural abundance ( 13 C/ 12 C isotope ratios) of C3 and C4 crops is a good natural tracer of organic inputs to the soil (Dong et al. 2019;Sun et al. 2021). ...
... Tallgrass prairies are undoubtedly water-limited; rates of net CO 2 assimilation (A) and stomatal conductance of H 2 O vapor (g sw ) of many C 3 and C 4 grass species decline when rainfall is limited (Ripley et al. 2010;Taylor et al. 2010Taylor et al. , 2011Taylor et al. , 2014. For this reason, drought suppresses aboveground net primary production (ANPP) in most North American grasslands (Carroll et al. 2021). ...
... A 50% decline in V cmax under drought can impose significant metabolic limitations on photosynthesis, decoupling the relationship between A and g sw (Ripley et al. 2010). Indeed, reduced A is a common consequence of drought for both C 3 and C 4 species (Taylor et al. 2011) . Yet we found no evidence that drought affected A, g sw , V cmax , J max , or biomass production, nor did drought appear to strengthen metabolic limitations by weakening the A-g sw relationship. ...
Seasonal changes in soil moisture drive the phenology of grassland plants during the growth period, yet we do not understand the biochemical processes underlying seasonal changes in grass photosynthesis. This lack of understanding at least partially stems from the paucity of information describing the metabolic and stomatal responses of dominant C4 grass species to drought. Here, we characterized seasonal patterns in plant physiology, including stomatal and non-stomatal limitations of photosynthesis, for two dominant C4 grass species, Bouteloua curtipendula and Schizachyrium scoparium. We also tested how rainfall reduction might modify seasonal patterns in photosynthesis for both species. Specifically, we predicted that drought would reduce carboxylation (Vcmax) and electron transport (Jmax), thereby limiting net CO2 assimilation (A) and suppressing biomass for Bouteloua curtipendula and Schizachyrium scoparium. We tested these predictions using the first in situ drought experiment to measure the impact of drought on C4 physiology. Our results demonstrate that photosynthesis of co-occurring, dominant C4 grasses is primarily limited by RuBP regeneration. Interestingly, Jmax was not reduced by drought for either B. curtipendula or S. scoparium, enabling both species to maintain constant A under drought. Seasonal changes in soil moisture did decrease Jmax, which in turn reduced A, for S. scoparium. Photosynthesis of B. curtipendula, on the other hand, remained stable throughout the growing season. That two common C4 species possess such different biochemical and photosynthetic responses to soil moisture highlights the physiological variability inherent within plant functional groups, and underscores the need for more field studies of C4 biochemistry.
... Crops convert atmospheric CO 2 into SOC, thus linking the abiotic and biotic components of the carbon (C) cycle. Field crops are normally grouped into C3 and C4 categories with different photosynthetic efficiency (Taylor et al. 2015). Generally, C4 crops (e.g., maize and sorghum) have higher photosynthetic activity and CO 2 assimilation rates compared with C3 crops (e.g., wheat and rice) (Taylor et al. 2015). ...
... Field crops are normally grouped into C3 and C4 categories with different photosynthetic efficiency (Taylor et al. 2015). Generally, C4 crops (e.g., maize and sorghum) have higher photosynthetic activity and CO 2 assimilation rates compared with C3 crops (e.g., wheat and rice) (Taylor et al. 2015). The stable C isotope 13 C based on natural abundance ( 13 C/ 12 C isotope ratios) of C3 and C4 crops is a good natural tracer of organic inputs to the soil (Dong et al. 2019;Sun et al. 2021). ...
In the context of climate change, soil is a major pool of stable carbon on earth, yet knowledge on soil carbon turnover is limited. The difference in 13C/12C content observed between C3 and C4 plant crops has been widely used to distinguish the sources of soil organic carbon under continuous monoculture, but not in C3–C4 rotations. We studied the stability of the δ13CSOC content and the effect of no tillage, conventional tillage, and rotary tillage in 4 soils sampled at 0–5, 5–10, and 10–20 cm depth, in 2018–2019 in a field with long-term history of wheat (C3) and maize (C4) rotations. We also analyzed the results from the literature. The results show that the δ13CSOC is not statistically affected by the sampling date, thus allowing to use this method to distinguish C3 and C4 plant contributions in rotations. Moreover, no-tillage favored the preservation of wheat carbon, and this preservation was accentuated at 10–20 cm depth. δ13CSOC is also affected by fertilization and irrigation. The literature confirmed that wheat-derived carbon is better preserved that maize-derived carbon, on the average.
... In overview, C4 plants are recognized to be more tolerant to drought than C3, mainly due to the compensation of stomatal limitation by carbon concentration mechanism and re-fixation of photorespired CO 2 (Ghannoum 2009). However, this behaviour is not as clear in longterm or severe drought events (Taylor et al. 2011). In general, the gas-exchange results of this study are in agreement with both above-mentioned patterns: C4 advantages at moderate water deficit and lost of the advantage in more severe limitation. ...
... supports its qualification as specialist. This may also help to explain the fact that C4 species may lose their evolutive-acquired advantages in long-term or severe drought events (Taylor et al. 2011). ...
C3 and C4 plants, as their intermediates, respond differently to short-term changes in environmental conditions. This difference is linked to contrasting levels of phenotypic plasticity and photosynthetic apparatus specialization. Phenotypic plasticity is an underexplored topic although its understanding is crucial to predict plant behaviour in future climatic scenarios. In this research, the phenotypic plasticity of anatomical traits and its influence to carbon uptake efficiency was studied in plants with different photosynthetic types, under contrasting water regimes. Oryza sativa cvs. Soberana (drought-sensitive) and Douradão (drought-tolerant) (C3), Homolepis isocalycia (C3 proto-Kranz) and Andropogon gayanus (C4), grown at three water treatments (100, 75 and 50% of substrate water holding capacity), were phenotyped for leaf anatomy and gas-exchange parameters. The results showed that plasticity trends indicated different strategies between O. sativa cultivars to deal with water shortage, explaining their classification as drought-sensitive or tolerant. We also mapped typical characteristics of C3–C4 intermediate plant, H. isocalycia, mainly in the ratio mesophyll:bundle sheath cells and hypothesize how it may influence photosynthesis. Finally, we have confirmed previous claims that C4 carbon uptake advantages may be limited under severe drought conditions, as A. gayanus have drastically reduced its photosynthetic rates at lower water levels. By studying C3–C4 intermediates, this study may also be a starting point to unravel the trade-offs of anatomical changes during the evolutionary process from C3 to C4 photosynthesis, and also improve the understanding of their impact in carbon uptake in different water conditions.
... This does not hold true for barley, where moderate water shortage reduced leaf Si content by nearly 40% [23]. The differences regarding Si uptake might also arise due to different water-use efficiencies, which are significantly higher in C 4 plants compared to C 3 plants [24]. Indeed, Si is especially important for grasses, where its deposition in the plant tissues provides structural rigidity to leaves and stems, and thereby prevents plant lodging [25]. ...
... Afterwards, they were measured an additional seven times, to the end experimental period. The first five soil moisture measurements were~6 days apart (days 0, 6,12,17,24), while the remaining three measurements were carried out within the last week of the experimental period (days 25,27,32). The soil temperatures were recorded once every 2 h from 28 June to 17 July, 2018 (days 13-32), using water temperature data loggers (UTBI-001 TidbiT v2; Onset Computer Corporation, Bourne, MA, USA). ...
Climate change can result in extreme droughts, significantly affecting crop production. C4 crop proso millet (Panicum miliaceum L.) has the lowest water consumption among all of the cereal crops. Understanding its survival mechanisms is thus crucial for agriculture. Furthermore, yield reduction does not only occur directly due to water shortage, but is also a consequence of an impaired element uptake during drought. This study aimed to examine the effect of water deficiency on proso millet leaf traits, plant biomass partition, and yield. In addition, leaf element contents were analysed, including silicon, which is an important multifunctional element for grasses. The majority of the measured parameters showed little change from the control to the moderate and severe water shortage treatments, even though the soil moisture levels differed significantly. The most pronounced reduction in comparison to the control was for leaf biomass, leaf stomatal conductance, and leaf silicon, phosphorus, calcium, and sulphur contents. Conversely, an increase was obtained for leaf potassium and chlorine contents. Panicle biomass was the same for all plant groups. Leaf silicon was positively correlated to reflectance in the UV region, while leaf calcium was negatively correlated to reflectance in the visible regions, which might prevent damage due to shortwave UV radiation and provide sufficient visible light for photosynthesis. The efficient light and water management, reduction of leaf biomass, and same-sized root system may be the mechanisms that mitigate the negative effects of water shortage in proso millet.
... C4 plants are recognized to be more drought tolerant than C3 species, mainly due to faster fixation of Carbon dioxide than C3 plants (Ghannoum 2009). However, this behaviour is not clear in longterm or severe drought events (Taylor et al. 2011). The C4 grasses generally are more drought tolerant and less shade tolerant (i.e., need more light) for photosynthesis than C3 crops, and sites under trees yieldedless grass that sites in open conditions during the second phase. ...
Rehabilitation of degraded land is considered one of the most important issues in the present era. Cultivation of fruit trees is considered an effective strategy to utilize degraded land and combat the issue of desertification sustainably. Therefore, a long-term (1995–2015) land use experiment was conducted to observe the response of peach (Prunus persica L.) trees to various soils composition ratios (soil (A) %: gravel (G) %: manure (M), kg tree⁻¹ under irrigation or rainfed (RF) conditions. Treatments included: T1 (S20:G80:M80), T2 (S50:G50:M70), T3 (S75:G25:M60), T4 (S100:G0:M50) under irrigation and T5 (S100:G0:M50) in rain-fed conditions. The study of peach-based land uses (PBLUs) evaluated the long-term impact of treatment on canopy spread, fruit yield, litter production, crop yield, residues biomass, soil moisture, biomass production, carbon stocks, and system economics in the degraded lands of the western Himalaya. The black gram (Vigna mungo L. Hepper) – toria- (Brassica juncea L. Czern) based crop rotation was practiced (1996–2005), followed by the cultivation of naturalized grasses (Sorghum halepene, Panicum maximum, P. notatum) to best utilize the available interspaces (2006–2010). Peach trees grown on only soil (i.e., no gravel) with 17.6% clay under drip irrigation (T4) had greater fruit yield (11.44 t ha⁻¹), more litter production (3.05 t ha⁻¹), and better intercrops yield (0.92 t ha⁻¹) during the first phase (1996–2005) and greater fruit yield (12.58 t ha⁻¹), more litter production (6.08 t ha⁻¹) and better intercrop perennial grass yield (1.45 tha⁻¹) during the second phase (2006–2015), compared to the rest of the treatment combinations. Likewise, the T4 treatment produced greater dry biomass of peach tree plus intercrops (63.62 t ha⁻¹), more aboveground carbon stocks (29.90 t C ha⁻¹), and greater soil carbon stocks (40.90 t C ha⁻¹). In terms of economics, growing trees with soil and irrigation resulted in greater net present value NPV ($22700 ha⁻¹), larger benefit:cost ratio (3.13:1), and higher internal rate of return (39.90%) with a shorter minimum payback period (3.10 years). This was followed by growing peaches with limited gravel in the media (T3) or with only soil but without irrigation (T5). Hence, the present study recommends 100% soil followed by 75% soil with irrigation practices when using peach-based agroforestry practices to rehabilitate degraded lands and improve ecosystem services under these edaphoclimatic conditions.
... Our δ 13 C values are consistent with C 3 vegetation, consistent with the present-day low proportion of C 4 plants in the Azores of only ∼4%, although almost half of its vegetation cover has been affected by human activity (Collins & Jones, 1986). The scarcity of water-stress thriving C 4 vegetation could indicate the absence of long periods with prevailing dry conditions (e.g., Ghannoum, 2009;Taylor et al., 2011), also pointing to the south-centered or weakened Azores High. The δ 13 C values are consistent with our paleoecological reconstruction based on PS elemental geochemistry, which indicates that PSs were formed under a humid forest all over the last 1 Myr in the Eastern and Central Azores (Figure 4). ...
The late Quaternary paleoclimate of the North Atlantic region has been widely studied, but the local terrestrial response to broader climatic variations remains underexplored. The Azores Archipelago, influenced by the North Atlantic Oscillation (NAO) and the Azores High, is a strategic target to investigate such interactions. Here, paleosols developed in equilibrium with the atmosphere recorded environmental variations in their geochemistry, and volcanic units sealing those paleosols allow for their precise dating. Clay mineralogical transfer functions from paleosol geochemistry and geochronological data were used to track paleoclimatic and paleoecological changes in this region over the past 1.3 Myr. Mean annual precipitation and air temperature reconstructions range from 620 to 1,520 mm yr⁻¹ and 14–26°C, with the latter tightly coupled with previous reconstructions of sea surface temperature. New K‐Ar ages evidence pulsed soil formation periods under weathering‐favorable wet and warm conditions, suggesting periods of a persistent negative NAO with a weakened or more southern Azores High after glacial Terminations I, II, IV, V, IX, and X. Our humidity province reconstructions indicate a prevailing moist to wet forest under cool temperate to subtropical conditions, with less variability than continental Europe. A rapid paleoecological shift occurred at ∼430 ka in São Miguel Island, probably associated with the high amplitude of Termination V. Paleoecological changes younger than 430 ka could be related to local, not large‐scale, climate changes. Average past precipitations were ∼170 mm yr⁻¹ lower than in the present, which suggests that modern weathering rates are higher than observed in our record.
... Larger widening exponent) toward the leaf tip and resulting in carbon savings to the plant. It is interesting that the widening exponent correlated better with A than g s*wv , and we can think of two possible explanations: (1) Given that g s*wv is highly dynamic and often responds more quickly than A to a variety of environmental conditions (Fletcher et al., 2007;Ripley et al., 2010;Taylor et al., 2011;Ocheltree et al., 2014), it may be that A in this study better reflects the maximum rates of gas exchange expected for these plants. ...
The widening of xylem vessels from tip to base of trees is an adaptation to minimize the hydraulic resistance of a long pathway. Given that parallel veins of monocot leaves do not branch hierarchically, vessels should also widen basipetally but, in addition to minimizing resistance, should also account for water volume lost to transpiration since they supply water to the lamina along their lengths, that is ‘leakiness’.
We measured photosynthesis, stomatal conductance, and vessel diameter at five locations along each leaf of five perennial grass species.
We found that the rate of conduit widening in grass leaves was larger than the widening exponent required to minimize pathlength resistance (0.35 vs c. 0.22). Furthermore, variation in the widening exponent among species was positively correlated with maximal stomatal conductance (r² = 0.20) and net CO2 assimilation (r² = 0.45).
These results suggest that faster rates of conduit widening (> 0.22) were associated with higher rates of water loss. Taken together, our results show that the widening exponent is linked to plant function in grass leaves and that natural selection has favored parallel vein networks that are constructed to meet transpiration requirements while minimizing hydraulic resistance within grass blades.
... Carmo-Silva et al. (2007) showed strong photosynthetic downregulation in three C 4 grasses with different decarboxylating mechanisms, subject to the addition of polyethylene glycol to the nutrient solution 20-26 h before measurements. Comparative studies of related C 3 and C 4 grasses show that C 4 species experience greater reductions in photosynthetic rates during drought compared with C 3 species both in controlled (Taylor et al., 2011) and in common garden conditions (Ripley et al., 2007. Ward et al. (1999) found, in a pot study, that the sensitivity of assimilation to dehydration was 136% higher for C 4 Amaranthus retroflexus than for C 3 Abutilon theophrasti. ...
The high productive potential, heat resilience, and greater water use efficiency of C4 over C3 plants attract considerable interest in the face of global warming and increasing population, but C4 plants are often sensitive to dehydration, questioning the feasibility of their wider adoption.
To resolve the primary effect of dehydration from slower from secondary leaf responses originating within leaves to combat stress, we conducted an innovative dehydration experiment. Four crops grown in hydroponics were forced to a rapid yet controlled decrease in leaf water potential by progressively raising roots of out of the solution while measuring leaf gas exchange.
We show that, under rapid dehydration, assimilation decreased more steeply in C4 maize and sorghum than in C3 wheat and sunflower. This reduction was due to a rise of nonstomatal limitation at triple the rate in maize and sorghum than in wheat and sunflower.
Rapid reductions in assimilation were previously measured in numerous C4 species across both laboratory and natural conditions. Hence, we deduce that high sensitivity to rapid dehydration might stem from the disturbance of an intrinsic aspect of C4 bicellular photosynthesis. We posit that an obstruction to metabolite transport between mesophyll and bundle sheath cells could be the cause.
... As compared to C3 plants, C4 plants exhibit higher photosynthesis rates, increased CO 2 fixation rates, as well as greater water use efficiency (WUE) and transpiration rates, highlighting their advantage. However, it's important to note that the photosynthetic process differs between C3 and C4 species under drought conditions (Taylor et al. 2011;Way et al. 2014;Hatfield and Dold 2019). Gas exchange in C4 plants was less affected by drought compared to C3 plants, as the earliest response to leaf water deficit is stomatal closure, which specifies the CO 2 diffusion limit into the chloroplast (Yan et al. 2016). ...
Plants rely on photosynthesis to convert light energy into chemical energy. However, their photosynthetic performance can be greatly affected by changes in the abiotic environment such as temperature, light intensity, and water availability. This draft summarizes the impact of changing abiotic conditions on photosynthetic adaptation in plants. Plants have developed various adaptive mechanisms to optimize their photosynthetic efficiency under different abiotic stresses. For example, under high light intensity, plants may regulate their photosynthetic apparatus by reducing the size of their light-harvesting antenna or increasing the activity of photorespiration. Similarly, under low water availability, plants can close their stomata to prevent water loss and reduce their photosynthetic activity, or activate molecular pathways to enhance drought tolerance. Understanding the molecular mechanisms underlying these adaptations is essential for developing strategies to improve crop productivity and sustainability under changing environmental conditions. Advances in molecular biology and biotechnology have provided new tools for identifying genes and proteins involved in photosynthetic adaptation in plants. These findings can be applied to develop crop varieties that are better adapted to different environmental conditions, such as drought, high temperatures, or high salinity. Despite the progress made in understanding the impact of changing abiotic environments on photosynthetic adaptation in plants, there are still many challenges to be addressed. The complex interactions between plants and their environment, as well as the potential effects of multiple stresses, require further investigation. In addition, there is a need to develop sustainable agricultural practices that can mitigate the negative impacts of climate change on crop productivity.
... Therefore, it is considered one of the main causes of death in plants (Luna-Flores et al., 2012). First, plants close stomata reducing the exchange of carbon dioxide (CO 2 ); these has a negative impact on plant growth (Engelbrecht and Schulz, 2001;Larcher, 2003, Garreaud et al., 2009) and instantaneous water use efficiency (WUE) could either show a decline or an increase in C3 species (Taylor et al., 2011). On the other hand, the water deficit also can produce morphological changes on plants, such as a decrease in leaves and stems growth, smaller leaf area and a reduction of the specific leaf area (SLA, cm 2 gr − 1 ) (Engelbrecht and Schulz, 2001). ...
In arid environments, stochastic rainfall and high evapotranspiration force plants to optimize water resources.
North Patagonia is characterized by a deep rainfall gradient that gives rise to environments with very contrasting water availability. Festuca pallescens is a key native forage species, growing widely in those environments. To explore morphological and physiological traits involved in the response to drought, we exposed plants from populations sampled along the rainfall gradient to different water availability conditions (Well-watered, Waterpulse,Water-drought). We evaluated morphological traits in all populations to assess inter-population variability and physiological traits between selected populations from sub-humid and arid environments to explore possible macro-environmental responses. Populations showed variation in survival after 45 days of drought conditions and differences in the expression of morphological traits. Also, populations from arid environments were less affected than those from humid environments, showing a longer recovery when they received water pulses. Although a population survival pattern related to the rainfall gradient was not evident, populations from arid environments exhibited local adaptation to their home environments, taking better advantage of water pulses. These results provide information about the response of a non-model species to environments with contrasting water availability and possibly, to changing rain patterns in arid environments under climate change.
... Continuous water stress reduces CO 2 assimilation and inhibits the plant growth [47]. Especially the plants with C3 photosynthetic pathways (including major cereal crops like wheat, rice, barley, oats) have lower water-use efficiency, leaf photosynthesis and chlorophyll content under drought conditions [48]. showed an increase in the biomass and phosphorous content upon the addition of lignin hydrogel and sodium polyacrylate hydrogel [57]. ...
Hydrogels retain substantial quantities of both water and nutrients within their three dimensional polymeric network. As such they have the ability to modify the local micro-environment of seeds/seedlings to enhance their growth outcomes. In terms of both safety and sustainability, the use of natural biopolymer based hydrogels is more advantageous. The network structure of hydrogels is typically formed by physical interaction and/or chemical crosslinking between polymer chains. The nature, strength and extent of crosslinking can be tailored to customize gel properties (such as mechanical strength, porosity and swelling behaviour) to suit a given type of application. This review highlights the use of hydrogels in agriculture where they (i) provide drought resistance to crops, (ii) act as reservoirs for critical nutrients, (iii) function as seed coating agents and (iv) improve transplantation success rate. The biodegradability and environmental compatibility of hydrogels for a range of applications in the farming sector is also discussed. Finally, the challenges of modifying hydrogels to suit specific agricultural applications are elaborated including issues that need to be overcome to exploit the full potential of these novel soft materials in sustainable farming practices of the future.
... This suggests that drought-induced inhibition of photosynthesis in C. ciliaris might be of stomatal rather than metabolic origin. Previous studies have also shown that photosynthesis in water-stressed C 4 plant species was mainly limited by stomata with both rapidly and slowly imposed water deficits (Da Silva & Arrabaca, 2004;Taylor et al., 2011). The decrease in stomatal conductance in C. ciliaris might have led to reduced CO 2 availability to chloroplasts and, consequently, limited photosynthesis. ...
Background
Few studies have evaluated the effect of drought on the morpho‐physiological characteristics of African C4 grasses. We investigated how drought affects leaf gas exchange characteristics, biomass partitioning, and water use efficiencies of Enteropogon macrostachyus and Cenchrus ciliaris.
Methods
The grasses were grown in a controlled environment under optimum conditions, that is, 70% of the maximum water‐holding capacity (WHC) for the first 40 days. Thereafter, half of the columns were maintained under optimum or drought conditions (30% of maximum WHC) for another 20 days.
Results
Under optimum conditions, C. ciliaris showed a significantly higher photosynthetic rate, stomatal conductance, and transpiration rate than E. macrostachyus. Drought decreased the photosynthetic rate, stomatal conductance and transpiration rate only in C. ciliaris. The net photosynthetic rate, stomatal conductance, and leaf transpiration of E. macrostachyus did not differ significantly under optimum and drought conditions. E. macrostachyus showed an increase in its water use efficiencies under drought to a greater extent than C. ciliaris.
Conclusions
Our results demonstrate that C. ciliaris is more sensitive to drought than E. macrostachyus. The decrease in the intercellular CO2 concentration and the increase in stomatal limitation with drought in C. ciliaris and E. macrostachyus suggest that stomatal limitation plays the dominant role in photosynthesis of the studied African C4 grasses.
... The vulnerability of belowground bud banks differs among plant functional groups, with consequences for plant composition and ecosystem function (Taylor et al., 2011;Mackie et al., 2019). For example, functional groups with greater bud density and/or conservative leaf water use traits (e.g., lower specific leaf area and high (Xu et al., 2017). ...
Climate change is expected to increase the magnitude and frequency of extreme drought in most grassland ecosystems. Exploring the responses of below‐ground bud banks and their relationships with above‐ground plant structure and drought is need to explain how climate change will impact grassland ecosystems. However, studies on the response of community‐scale bud and shoot densities to experimental drought along an aridity gradient are rare.
We experimentally removed 66% of growing season precipitation for 4 years in three temperate grasslands that spanned an aridity gradient in northern China. We quantified the legacy effects of drought on grass, forb and total community below‐ground bud density, above‐ground shoot density and the ratio of bud to shoot density 1 year following treatment.
Below‐ground bud density was lowest at the highest aridity site for the entire community, while above‐ground shoot density was highest at the medium aridity site. Below‐ground bud and above‐ground shoot densities were the lowest at the high aridity site for grasses but the highest for forbs at this site. Bud:shoot ratios decreased with increasing aridity for grasses, yet remained constant for forbs along the aridity gradient. Below‐ground bud density in drought plots remained lower than controls a year following drought at each site. Experimental drought did not alter the below‐ground bud bank for grasses but decreased forb bud banks across sites. Experimental drought had little legacy effects on above‐ground shoot density and bud:shoot ratios for grasses, forbs and the total community at each site.
Our results suggest that grass and forb bud banks can differ in their responses to both multi‐year drought along an aridity gradient, and that bud limitation for shoot generation may increase as grasslands get drier. Bud bank responses to climate will impact plant community functioning and resilience. Thus, incorporating bud bank dynamics will improve projections of grassland ecosystems under future climate change.
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... In general, grasslands are composed of two dominant herbaceous functional groups: grass and forb, which show great differences in their vulnerability to extreme drought (Taylor et al., 2011;Wilcox et al., 2020). Grass species are generally better able to tolerate drought, especially C4 grasses, whereas forb species may avoid drought via deeper rooting profiles (Nippert and Knapp, 2007). ...
Grasslands are structurally and functionally controlled by water availability. Ongoing global change is threatening the sustainability of grassland ecosystems through chronic alterations in climate patterns and resource availability, as well as by the increasing frequency and intensity of anthropogenic perturbations. Compared with many studies on how grassland ecosystems respond during drought, there are far fewer studies focused on grassland dynamics after drought. Compensatory growth, as the ability of plants to offset the adverse effects of environmental or anthropogenic perturbations, is a common phenomenon in grassland. However, compensatory growth induced by drought and its underlying mechanism across grasslands remains not clear. In this review, we provide examples of analogous compensatory growth from different grassland types across drought characteristics (intensity, timing, and duration) and explain the effect of resource availability on compensatory growth and their underlying mechanisms. Based on our review of the literature, a hypothetic framework for integrating plant, root, and microbial responses is also proposed to increase our understanding of compensatory growth after drought. This research will advance our understanding of the mechanisms of grassland ecosystem functioning in response to climate change.
... In addition, although the drought degree is the most serious in Golmud, the tradeoff intensity be-tween photosynthesis and water use of the community was lower than that in Nuomuhong. This phenomenon may have been caused by differences between species: C.k. (C4) is the main species in the plant community in Golmud; C4 plants are more resilient to drought stress in terms of stomatal conductance and hydraulic performance than C3 plants, thus maintaining their photosynthetic advantage [45,46]. ...
Leaf functional traits in drylands are sensitive to environmental changes, which are closely related to plant growth strategies and resource utilization ability and can reflect the balance of substance synthesis and water loss. However, the influence of environmental factors on photosynthetic production traits and water use traits is still unclear in drylands. In this study, nine environmental factors (climatic characteristics and soil physical and chemical properties), leaf net photosynthetic rate (A), transpiration rate (E), and stomatal conductance (GSW) were measured via 60 plant samples and 45 soil samples, which were collected at five sampling sites according to rainfall gradient. Redundancy analysis (RDA), structural equation model (SEM), and regression analysis were used to analyze the influencing mechanism of drought on photosynthetic production traits and water use traits. The results provided the following conclusions: (i) The hydrothermal condition determined A, E, and GSW by affecting the spatial distribution of soil nutrients (SN) and soil salinity (SS); meanwhile, temperature was able to affect A, E, and GSW directly. (ii) The water content (WC) was the key driver of the strength of the synergistic relationship between photosynthetic production traits and water use traits; soil salinity (SS) was the main driver of the synergistic relationship between E and GSW.
... This superstructure involves a carbon-concentrating mechanism that makes it possible to use light and water more efficiently at high temperatures and under water deficits owing primarily to the nearly absolute refixation of photorespiratory CO 2 . In general, C4 plants grow faster than plants with C3 photosynthesis (Sage and McKown 2006;Ghannoum 2009;Ripley et al. 2010;Taylor et al. 2011;Way et al. 2014;Rakhmankulova et al. 2019) and these groups of plants usually differ phylogenetically (Zacharias and Baldwin 2010) . ...
Atriplex tatarica (Chenopodiaceae) is an herbal species that is native throughout a wide area of Middle and western Central Asia, Asia Minor, Eastern Europe, and North Africa. It is an annual diploid plant that is propagated by achenes only, which it produces in large quantities. Achenes are part of the persistent seed bank. This species tolerates summer drought and soil salinity well. Ongoing climate change brings suitable conditions for the rapid spread of this sub-halophytic alien species, especially around transportation corridors in the lowlands and warmer regions of Central Europe. The characteristics that predispose A. tatarica to successfully spread around major roads and motorways are explained in this text.
Link: https://rdcu.be/cTihu
... Low soil moisture negatively impacts growth, increases xylem tension, and decreases 334 carbon assimilation [85,86]. The ability to mitigate and recover from drought is based on 335 anatomical and physiological traits [87,88]. While the impacts of severe drought on the 336 physiology of grassland species have been observed in previous research, few studies combined 337 physiological, whole-leaf, and anatomical trait data [47,89]. ...
Grasses are cosmopolitan, existing in many biome and climate types from xeric to tropical. Traits that control physiological responses to drought vary strongly among grass lineages, suggesting that tolerance strategies may differ with evolutionary history. Here, we withheld water from 12 species representing six tribes of grasses to compare how species respond to drought in different grass lineages. We measured physiological, morphological, and anatomical traits. Dominant lineages from tropical savannas, like Andropogoneae, tolerated drought due to above and belowground morphological traits (specific leaf area and root length, SLA and SRL), while temperate grasses in this study utilized conservative leaf physiology (gas exchange) and anatomy traits. Increased intrinsic water-use efficiency coincided with a larger number of stomata, resulting in greater water loss (with inherently greater carbon gain) and increased drought sensitivity. Inherent leaf and root economic strategies impacting drought response were observed in all species, resulting in either high SLA or SRL, but not both. Our results indicate that grasses subjected to severe drought were influenced by anatomical traits (e.g., number of stomata and xylem area) and similar within lineages. In addition, grasses recovered at least 50% of physiological functioning across all lineages and 92% within Andropogoneae species, illustrating how drought can influence functional responses across diverse grass lineages.
... This means that at low moisture, the processes involved in the remediation of Kastanozem soil proceed more intensely in the rhizosphere of alfalfa than they do in the rhizosphere of sorghum. With account taken of the findings of Taylor et al. (2011), who showed that the photosynthetic water-use and nitrogen-use efficiency advantages of C4 plants over C3 plants at normal moisture were sharply reduced under a moisture deficit, we believe that C3 plants may compete with C4 plants as soil remediators in arid regions. A similar situation in the competitive relationship between C3 and C4 plants can also occur at low stress (Nayyar and Gupta, 2006). ...
Many petroleum extraction and refinement plants are located in arid climates. Therefore, the remediation of petroleum-polluted soils is complicated by the low moisture conditions. We ran a 70-day experiment to test the efficacy of various combining of remediation treatments with sorghum, yellow medick, and biochar to remove petroleum from and change the biological activity of Kastanozem, a soil typical of the dry steppes and semideserts of the temperate zone. At normal moisture, the maximum petroleum-degradation rate (40%) was obtained with sorghum–biochar. At low moisture, the petroleum-degradation rate was 22 and 30% with yellow medick alone and with yellow medick − sorghum, respectively. Biochar and the biochar-plant interaction had little effect on soil remediation. Both plants promoted the numbers of soil microbes in their rhizosphere: yellow medick promoted mostly hydrocarbon-oxidizing microorganisms, whereas sorghum promoted both hydrocarbon-oxidizing and total heterotrophic microorganisms. Low moisture did not limit microbial development. In the rhizosphere of sorghum, dehydrogenase and urease activities were maximal at normal moisture, whereas in the rhizosphere of yellow medick, they were maximal at low moisture. Peroxidase activity was promoted by the plants in unpolluted soil and was close to the control values in polluted soil. Biochar and the biochar-plant interaction did not noticeably affect the biological activity of the soil.
... reduced water loss) without compromising carbon assimilation (Taylor et al., 2010;Vogan and Sage, 2011;Osborne and Sack, 2012), which raises the possibility that C 4 photosynthesis might have been selected as a water-conserving mechanism (Osborne and Sack, 2012) and that water limitation might be a primary driver of C 4 evolution (Williams et al., 2013;Reeves et al., 2018;Zhou et al., 2018). A comparison study on multiple independent lineages of C 4 grasses showed that the g s is substantially lower in C 4 species relative to C 3 relatives (Taylor et al., 2010(Taylor et al., , 2011, and that the higher intrinsic water-use efficiency (iWUE) of C 4 plants compared with that of C 3 plants can be attributed to both lower g s and higher photosynthetic CO 2 uptake rate (A) (Taylor et al., 2010;Uzilday et al., 2014;Kocacinar, 2015;Aubry et al., 2016). The high carbon assimilation capacity of C 4 plants contributes to their high biomass, while low g s is crucial for C 4 plants to better adapt to saline land, and hot, arid and open habitat (Powell, 1978;Sage, 2004). ...
C4 photosynthesis optimizes plant carbon and water relations, allowing high photosynthetic rates with low stomatal conductance. Stomata have long been considered a part of the C4 syndrome. However, it remains unclear how stomatal traits evolved along the path from C3 to C4. Here, we examined stomata in the Flaveria genus, a model used for C4 evolutionary study. Comparative, transgenic, and semi-in-vitro experiments were performed to study the molecular basis that underlies the changes of stomatal traits in C4 evolution. The evolution from C3 to C4 species is accompanied by a gradual rather than an abrupt change in stomatal traits. The initial change appears near the Type I intermediate stage. Co-evolution of the photosynthetic pathway and stomatal traits is supported. On the road to C4, stomata tend to be fewer in number but larger in size, and stomatal density dominates changes in anatomical maximum stomatal conductance (gsmax). Reduction of FSTOMAGEN expression underlies decreased gsmaxin Flaveria and likely occurs in other C4 lineages. Decreased gsmax contributes to the increase in intrinsic water use efficiency in C4 evolution. This work highlights the stomatal traits in the current C4 evolutionary model. Our study provides insights into the pattern, mechanism, and role of stomatal evolution along the road towards C4.
... The photosynthetic activity of C 3 and C 4 species is different under drought conditions. C 4 species can effectively maintain high WUE under drought conditions, which gives them a greater photosynthetic advantage than C 3 plants [18][19][20]. ...
One of the problems of sustainable agricultural land management (SALM) is the competition between food production and biomass production. For this reason, marginal lands with unfavorable agrotechnical conditions have been proposed for non-food crops in recent years. To this end, a better understanding of the impact of environmental factors on crop development and yield is needed. The objective of the study was to investigate the effects of soil water availability on selected morphological, physiological and growth characteristics of four C4 grass species (Miscanthus × giganteus, Miscanthus sacchariflorus, Miscanthus sinensis and Spartina pectinate) growing under different water and fertilizer conditions. A pot experiment was conducted under greenhouse conditions with four grass species, three different water rates (100, 85 and 70%) and three fertilizer rates (270, 180 and 90 kg NPK ha−1). The study showed that water stress, regardless of plant species, increased the chlorophyll content index without affecting the photosynthetic efficiency of the plants. Water stress significantly decreased plant fresh and dry mass, shoot number and length, and shoot/leaf ratio. The response to water deficit depended on the plant species. Miscanthus sinensis was the most sensitive to water deficit and Spartina pectinate the most tolerant (reduction in dry mass of 41.5% and 18%, respectively). Water stress (85% and 70%) reduced the number and the length of shoots without affecting the average diameter of shoots of the tested grasses, resulting in a significant reduction in biomass production of plants grown under optimal conditions with mineral NPK fertilization (180 kg NPK ha−1). Miscanthus sacchariflorus showed the highest dry matter under the worst growing conditions (70% and 90 NPK) and therefore could be recommended for cultivation on marginal lands with unfavorable agrotechnical conditions. It should be emphasized that the high yield of this species was not due to the photosynthetic efficiency, but better growth stem parameters (length and number). It appears that, for long-term agricultural land management, it is preferable to determine fertilizer rates for each crop species based on soil water availability. It should also be emphasized that increasing the yield of potential lignocellulosic crops for energy purposes while reducing environmental impact appears to be one of the viable answers to the difficulties of conventional energy production.
... In nature, drought tolerance and drought sensitivity occurs in both C3 and C4 plants. Furthermore, it cannot be ruled out that there is causal relationship between drought tolerance and C4 photosynthesis and hence, no specific correlation can be established between the type of photosynthesis and drought tolerance (Taylor et al., 2011). ...
... C 4 plants have a photosynthetic apparatus effective in warm and dry habitats. The C 4 species' high water use efficiency (WUE) led to the general consensus that plants with C 4 photosynthesis are drought tolerant [2]; however, some studies have provided more current information on the low drought tolerance of some C 4 species [3,4]. Sage and McKown [5] suggested that some unique functions of C 4 photosynthesis, and a more complex biochemical pathway, can reduce the potential for general phenotypic plasticity and the acclimatisation of photosynthesis to environmental changes. ...
The effects of water deficiency (–0.3 MPa) on plant growth, the water and proline content, fluorescence parameters chlorophyll PSI and II, and CO2/H2O gas exchange in plant leaves were studied in two populations of xero-halophyte Atriplex tatarica L. (C4 NAD-ME) with contrasting productivity. Based on growth parameter analysis, a less-productive population (P1) was more tolerant of osmotic stress, and a more-productive population (P2) was less tolerant. The studied populations demonstrated different ways of maintaining the water balance in leaves. P1 was characterised by an insensitivity of its stomatal apparatus, a significant decrease in water potential of mesophyll cells’ apoplast in substomatal cavity, an increase in proline content, and activation of PSI cyclic electron transport in leaves. In P2, maintaining the water content in leaves under stress conditions was achieved by stomatal closure. The impact of stress was manifested by decreased intensity of photosynthesis, transpiration, PSII efficiency and more intensified of dark respiration in P2. Thus, various ways by which to maintain the water balance in plant leaves in two populations were revealed under weak osmotic stress.
... Photosynthetic activity in C 3 and C 4 species is significantly different under drought conditions. C 4 species can effectively preserve high WUE under drought conditions, thus have a higher photosynthetic advantage than C 3 plants (Taylor et al., 2011;Way et al., 2014;Hatfield and Dold, 2019). ...
Drought stress affects a range of plant processes. It is still not well-known how C3 and C4 plants respond to drought. Here, we used a combination of meta-analysis and network analysis to compare the transcriptional responses of Oryza sativa (rice), a C3 plant, and Zea mays (maize), a C4 plant, to drought stress. The findings showed that drought stress changes the expression of genes and affects different mechanisms in the C3 and C4 plants. We identified several genes that were differentially expressed genes (DEGs) under stress conditions in both species, most of which are associated with photosynthesis, molecule metabolic process, and response to stress. Additionally, we observed that many DEGs physically located within the quantitative trait locus regions are associated with C isotope signature (d¹³C), photosynthetic gas exchange, and root characteristics traits. Through the gene co-expression and differential co-expression network methods, we identified sets of genes with similar and different behaviors among C3 and C4 plants during drought stress. This result indicates that mitogen-activated protein kinases (MAPK) signaling pathway plays an important part in the differences between the C3 and C4 species. The present study provides a better understanding of the mechanisms underlying the response of C3 and C4 plants to drought stress, which may useful for engineering drought tolerance in plants.
... at the beginning of crop development, may have been the factor that influenced competition among weeds the most during the carrot cultivation cycle in the drip irrigation system. As a C4 metabolism plant, this damaging species is better adapted to more intense temperature and light, presenting greater efficiency in the use of water (TAYLOR et al., 2011). Therefore, the lower availability of water in this system may have intensified competition for this resource, limiting the growth and development of the crop. ...
Weed interference is one of the factors that reduces carrot yield considerably. The aim of this study was to determine the periods of weed interference in carrots cultivated under two localized irrigation systems. The experiment used a completely randomized block design, with three replications, using the split plot scheme. The plots consisted of two irrigation systems (drip and micro sprinkler) and the subplots corresponded to the duration of coexistence of the crop with weeds, comprising periods of control (weed-free) or coexistence (with weeds) (0, 10, 20, 30, 40, 50, and 120 days after emergence (DAE) of the crop). Considering a yield loss of 2.5%, 5%, and 10% in marketable carrots, the beginning and end of the critical period of weed control (CPWC) was determined by adjusting a sigmoid model to the relative production data. The presence of the weed community throughout the crop cycle resulted in yield losses of up to 98%. The CPWP varied for the irrigation systems used. Carrot cultivation with and without competition, under the micro sprinkler irrigation system showed a higher yield than with the drip system. Considering a yield loss of 5%, the CPWC was 23 DAE and 7 DAE in the drip irrigation and micro sprinkler irrigation systems, respectively.
... PNUE in the C4 photosynthetic plant is generally greater than that in the C3 plant [24]. In addition, C4 plants are tolerant to drought stress [44] and have higher photosynthetic wateruse efficiency (PWUE) than C3 plants [45]. However, unlike PNUE and PWUE, our results clearly showed that the average PIUE value collected from sorghum varieties (which have C4 photosynthesis) was significantly decreased by Fe-deficiency ( Figure 4C). ...
Leaf iron (Fe) contents in Fe-deficiency-tolerant plants are not necessarily higher than that in Fe-deficiency-susceptible ones, suggesting an unknown mechanism involved in saving and allowing the efficient use of minimal Fe. To quantitatively evaluate the difference in Fe economy for photosynthesis, we compared the ratio of CO2 assimilation rate to Fe content in newly developed leaves as a novel index of photosynthetic iron-use efficiency (PIUE) among 23 different barley (Hordeum vulgare L.) varieties. Notably, varieties originating from areas with alkaline soil increased PIUE in response to Fe-deficiency, suggesting that PIUE enhancement is a crucial and genetically inherent trait for acclimation to Fe-deficient environments. Multivariate analyses revealed that the ability to increase PIUE was correlated with photochemical quenching (qP), which is a coefficient of light energy used in photosynthesis. Nevertheless, the maximal quantum yield of photosystem II (PSII) photochemistry, non-photochemical quenching, and quantum yield of carbon assimilation showed a relatively low correlation with PIUE. This result suggests that the ability of Fe-deficiency-tolerant varieties of barley to increase PIUE is related to optimizing the electron flow downstream of PSII, including cytochrome b6f and photosystem I.
... GCM data or interpolated data such as ISIMIP instead of RCM data), different DGVMs (Doherty et al., 2010;Gonzalez et al., 2010) and that precipitation changes until 2100 were not accounted for are hampered by low soil water availability (Nowak et al., 2004;Reich et al., 2014). On the other hand, advantages of C 4 grasses over C 3 grasses in dry habitats may be reduced under drought conditions (Taylor et al., 2011). ...
Anthropogenic climate change is expected to impact ecosystem structure, biodiversity and ecosystem services in Africa profoundly. We used the adaptive Dynamic Global Vegetation Model (aDGVM), which was originally developed and tested for Africa, to quantify sources of uncertainties in simulated African potential natural vegetation towards the end of the 21st century. We forced the aDGVM with regionally downscaled high‐resolution climate scenarios based on an ensemble of six general circulation models (GCMs) under two representative concentration pathways (RCPs 4.5 and 8.5). Our study assessed the direct effects of climate change and elevated CO2 on vegetation change and its plant‐physiological drivers. Total increase in carbon in aboveground biomass in Africa until the end of the century was between 18% to 43% (RCP4.5) and 37% to 61% (RCP8.5) and was associated with woody encroachment into grasslands and increased woody cover in savannas. When direct effects of CO2 on plants were omitted, woody encroachment was muted and carbon in aboveground vegetation changed between –8 to 11% (RCP 4.5) and –22 to –6% (RCP8.5). Simulated biome changes lacked consistent large‐scale geographical patterns of change across scenarios. In Ethiopia and the Sahara/Sahel transition zone, the biome changes forecast by the aDGVM were consistent across GCMs and RCPs. Direct effects from elevated CO2 were associated with substantial increases in water use efficiency, primarily driven by photosynthesis enhancement, which may relieve soil moisture limitations to plant productivity. At the ecosystem level, interactions between fire and woody plant demography further promoted woody encroachment. We conclude that substantial future biome changes due to climate and CO2 changes are likely across Africa. Because of the large uncertainties in future projections, adaptation strategies must be highly flexible. Focused research on CO2 effects, and improved model representations of these effects will be necessary to reduce these uncertainties. Climate change and elevated CO2 are expected to drive vegetation changes in Africa. We used an ensemble of dynamic vegetation model simulations to assess the impacts of these drivers on carbon stocks and biomes until 2099. Climate change and elevated CO2 led to an 18% to 61% increase in carbon stocks, which was primarily driven by CO2 fertilization. Associated biome changes are likely across Africa, especially changes from savanna to forest. Disabling CO2 fertilization resulted in a −22% to +11% change in carbons stocks. These large uncertainties in future projections imply that adaptation strategies need to be flexible.
... In the past decades, much research has challenged generalizations regarding how photosynthetic type has influenced the past and present distribution and ecology of C 3 and C 4 grasses, leading to a more nuanced understanding of the key roles of, for example, disturbance regime, phylogenetic history, and other traits not specific to photosynthetic type (42,43). For example, tolerance of water stress can in some cases be greater in C 3 than C 4 species (44). Indeed, when comparing traits of the North American C 3 vs. ...
Significance
During the Dust Bowl drought, central US grasslands responded unexpectedly to a decade of hot, dry conditions. Grass species adapted to high temperatures with higher water use efficiency (C 4 grasses) decreased, while those preferring cooler climates (C 3 grasses) increased. We reproduced this surprising response by experimentally imposing extreme drought in two native grasslands. Analysis of historical climate records revealed that during extreme drought years, the proportion of annual precipitation that occurs during cooler months increases. This previously unidentified shift in seasonal precipitation patterns during extreme drought years provides a mechanism for C 3 grasses to increase despite overall hot, dry conditions. Thus, alterations in precipitation seasonality may be as important as reduced precipitation amount when forecasting ecosystem responses to extreme drought.
... Although C 4 dominant managed pastures theoretically should have advantages in water limiting conditions over the NP with mixed C 3 and C 4 grasses that was not realized in our study. Several other studies (Briggs and Knapp, 2001;Nippert et al., 2007;Taylor et al., 2011;Tieszen et al., 1997) also reported that C 4 species failed to perform with the same higher intrinsic photosynthetic capacity (as measured in laboratory conditions) under field conditions and monoculture C 4 in our MP also showed lower adaptability in dry conditions. Some major differences in productivity of NP and MP in responses to the variability in environmental variables over 17 years are discussed below: ...
Future weather and climates, especially rainfall, are expected to have larger variability in the Southern Plains of the United States. However, the degree and timing of environmental variability that affect productivity of pastures managed differently have not been well studied. We examined the impacts of environmental variability on grassland productivity using 17 years of gross primary productivity (GPP) data for co-located native and managed prairie pastures in Oklahoma. We also considered the interactive effects of management factors and environmental variability into the regression models and identified the critical temporal windows of environmental variables (CWE) that influence annual variability in GPP. Managed pasture (MP) showed greater variability of GPP than did native pasture (NP), particularly with reduced GPP in drought years. The resilience of native prairies under unfavorable climate extremes was evident by lower GPP anomalies in NP than MP during the 2011–2012 drought. Although both pastures experienced the same degree of environmental variability, the CWE affecting GPP was significantly different between NP and MP due to the modulating impact of management practices on the responses of GPP. Not only the range but also the timings of the CWE were different between NP and MP as MP was more responsive to the spring temperature and fall rainfall. Our findings warrant the incorporation of MP as a different commodity from NP when accounting for the ecosystem responses to environmental variability in global climate models.
... C 4 grass species typically exhibit conservative regulation in stomatal aperture, because the biochemical adaptation for concentrating CO 2 inside bundle sheath cells maximizes carboxylation per unit water loss (Hatch, 1987;Edwards et al., 2001;Zhou et al., 2018). Relatively low variation (CV) in carbon-use tissues (Fig. 3A, C) reflects the innate biochemical adaptations of C 4 species, resulting in a lower quantum efficiency and a higher photosynthetic capacity than C 3 species (Taylor et al., 2011). While the C 4 biochemical strategy has an additional carboxylation step requiring additional ATP, the modified leaf anatomy (Kranz) allows greater overall carbon assimilation, which reduces the need for large structural leaf variation (CV) within species (Lundgren et al., 2014). ...
Background and aims:
Andropogon gerardii is a highly productive C4 grass species with a large geographic range throughout the North American Great Plains, a biome characterized by a variable temperate climate. Plant traits are often invoked to explain growth rates and competitive abilities within broad climate gradients. For example, plant competition models typically predict that species with large geographic ranges benefit from variation in traits underlying high growth potential. Here, we examined the relationship between climate variability and leaf-level traits in A. gerardii, emphasizing how leaf-level microanatomical traits serve as a mechanism that may underlie variation in commonly measured traits, such as SLA.
Methods:
A. gerardii leaves were collected in August of 2017 from Cedar Creek Ecosystem Science Reserve (MN), Konza Prairie Biological Station (KS), Platte River Prairie (NE), and Rocky Mountain Research Station (SD). Leaves from ten individuals from each site were trimmed, stained, and prepped for fluorescent confocal microscopy to analyze internal leaf anatomy. Leaf microanatomical data was compared with historical and growing season climate data which was extracted from PRISM spatial climate models.
Key results:
Microanatomical traits displayed large variation within and across sites. According to AICc selection scores, the interaction of mean precipitation and temperature for the 2017 growing season was the best predictor of variability for the anatomical and morphological traits measured here. Mesophyll area and bundle sheath thickness were directly correlated with mean temperature (annual and growing season). Tissues related to water-use strategies, such as bulliform cell and xylem area, were significantly correlated with one another.
Conclusions:
The results indicate (1) microanatomical trait variation exists within this broadly distributed grass species (2) microanatomical trait variability appears likely to impact leaf-level carbon and water use strategies, and (3) microanatomical trait values vary across climate gradients, and may underlie variation in traits measured at larger ecological scales.
... Hence, C 4 species have higher affinity for CO 2 and possess greater maximum velocity than C 3 species which fix CO 2 through ribulose-1,5-bisphosphate carboxylase-oxygenase (RuBisCO) at the carboxylation site (Ehleringer & Monson, 1993). C 4 species also have higher WUE relative to C 3 species (Long, 1999;Taylor, Ripley, Woodward, & Osborne, 2011;Wolf & Ziska, 2018). Despite variation among species, C 4 plants tend to occupy a drier niche than C 3 plants (Edwards & Smith, 2010;Osborne & Freckleton, 2009), implying that C 3 plants are more susceptible to water limitation than C 4 plants. ...
Biochar is a carbon (C)‐rich solid produced from thermochemical pyrolysis of biomass. Its amendment to soils has been proposed as a promising mean to mitigate greenhouse gas emissions and simultaneously benefit agricultural crops. However, how biochar amendment affects plant photosynthesis and growth remains unclear, especially on a global scale. In this study, we conducted a global synthesis of 74 publications with 347 paired comparisons to acquire an overall tendency of plant photosynthesis and growth following biochar amendment. Overall, we found that biochar amendment significantly increased photosynthetic rate (P n) by 27.1%, and improved stomatal conductance (g s), transpiration rate (E ), water use efficiency (WUE) and chlorophyll (Chl) concentration by 19.6%, 26.9%, 26.8% and 16.1%, respectively. Meanwhile, plant total biomass (TB), shoot biomass (SB), and root biomass (RB) increased by 25.4%, 22.1% and 34.4%, respectively. Interestingly, plant types (C3 and C4 plants) showed greater control over plant photosynthesis and biomass than a broad suite of soil and biochar factors. Biochar amendment largely boosted photosynthesis and biomass on C3 plants, but had a limited effect on C4 plants. Our results highlight the importance of the differential response of plant types to biochar amendment with respect to plant growth and photosynthesis, providing a scientific foundation for making reasonable strategies towards an extensive application of biochar for agricultural production management.
... Higher uptake of CO 2 at reduced intercellular CO 2 concentration (c i ) in C 4 plants allows equivalent or greater A at lower stomatal conductance (g s ) than in C 3 species [10,11], indicating that C 4 is characterized by maximal rates of net leaf photosynthesis (A) at a lower stomatal conductance than in C 3 species, also by lower transpiration and conserving water, especially in hot conditions when evaporative demand is high. Moreover, the authors of [12] conclude in their investigation that C 4 grasses in control treatments were characterized by higher CO 2 assimilation rates and water potential, but lower stomatal conductance and under drought, stomatal conductance declined more dramatically in C 3 than C 4 species. Furthermore, the authors of [13] have indicated that lower gs associated with C 4 photosynthesis may result in adaptation of plant hydraulics. ...
Grasslands have a natural capacity to decrease air pollution and a positive impact on human life. However, their maintenance requires adequate irrigation, which is difficult to apply in many regions where drought and high temperatures are frequent. Therefore, the selection of grass species more tolerant to a lack of irrigation is a fundamental criterion for green space planification. This study compared responses to deficit irrigation of different turfgrass mixtures: a C4 turfgrass mixture, Cynodon dactylon-Brachypodium distachyon (A), a C4 turfgrass mixture, Buchloe dactyloides-Brachypodium distachyon (B), and a standard C3 mixture formed by Lolium perenne-Festuca arundinacea-Poa pratensis (C). Three different irrigation regimes were assayed, full irrigated to 100% (FI-100), deficit irrigated to 75% (DI-75), and deficit irrigated to 50% (DI-50) of container capacity. Biomass, normalized difference vegetation index (NDVI), green area (GA), and greener area (GGA) vegetation indices were measured. Irrigation significantly affected the NDVI, biomass, GA, and GGA. The most severe condition in terms of decreasing biomass and vegetation indices was DI-50. Both mixtures (A) and (B) exhibited higher biomass, NDVI, GA, and GGA than the standard under deficit irrigation. This study highlights the superiority of (A) mixture under deficit irrigation, which showed similar values of biomass and vegetation indices under full irrigated and deficit irrigated (DI-75) container capacities.
... This indicates that the assimilation of soil moisture has increased the sensitivity of C3 grass to water stress. Since most of the C3 grass are from temperate regions and the photosynthesis for C3 is more dependent on water availability than C4 (Taylor et al., 2011), the C3 grass productivity reduction due to soil moisture deficit can therefore be detected by assimilation of soil moisture in CCDAS. Moreover, as shown in Fig. 2, those parameters such as inverse of leaf longevity (k L ), length of dry spell before leaf shedding (τ W ), the effect of temperature on soil respiration from the slow pool (Q 10,s ) the fraction of fast soil decomposition (f s ), ratio of maximum water supply rate (C W0 ) and emissivity of the atmosphere (emis0) are changed substantially. ...
The terrestrial carbon cycle is an important component of the global carbon budget due to its large gross exchange fluxes with the atmosphere and their sensitivity to climate change. Terrestrial biosphere models show large uncertainties in simulating carbon fluxes, which impact global carbon budget assessments. The land surface carbon cycle is tightly controlled by soil moisture through plant physiological processes. Accurate soil moisture observations thereby have the potential to improve the modeling of carbon fluxes in a model-data fusion framework. We employ the Carbon Cycle Data Assimilation System (CCDAS) to assimilate six years of surface soil moisture provided by the SMOS satellite in combination with global-scale observations of atmospheric CO 2 concentrations. We find that assimilation of SMOS soil moisture exhibits better performance on soil hydrology modeling at both global and site-level than only assimilating atmospheric CO 2 concentrations, and it improves the soil moisture simulation particularly in mid-to high-latitude regions where the plants suffer from water stress frequently. The optimized model also shows good agreements with inter-annual variability in simulated Net Primary Productivity (NEP) and Gross Primary Productivity (GPP) from an atmospheric inversion (Jena CarboScope) and the up-scaled eddy covariance flux product (FLUXNET-MTE), respectively. Correlation between SIF (Solar Induced Fluorescence) and optimized GPP also shows to be the highest when soil moisture and atmospheric CO 2 are simultaneously assimilated. In general, CCDAS obtains smaller annual mean NEP values (1.8 PgC/yr) than the atmospheric inversion and an ensemble of Dynamic Global Vegetation Models (DGVMs), but larger GPP values (167.8 PgC/yr) than the up-scaled eddy covariance dataset (FLUXNET-MTE) and the MODIS based GPP product for the years 2010 to 2015. This study demonstrates the high potential of constraining simulations of the terrestrial biosphere carbon cycle on inter-annual time scales using long-term microwave observations of soil moisture.
... Yet the determinants of grassland resilience to extreme drought remain poorly resolved. Grasslands are generally composed of two dominant herbaceous functional groups-grasses and forbs-which differ widely in their vulnerability to extreme drought (e.g., Taylor et al. 2011). In many grasslands, grasses are better able to tolerate drought because of their C 4 photosynthetic machinery (Ward et al. 1999), whereas forbs may avoid drought conditions via deeper rooting profiles (Nippert and Knapp 2007). ...
Climatic extremes, such as severe drought, are expected to increase in frequency and magnitude with climate change. Thus, identifying mechanisms of resilience is critical to predicting the vulnerability of ecosystems. An exceptional drought (<first percentile) impacted much of southern Africa during the 2015 and 2016 growing seasons, including the site of a long‐term fire experiment in Kruger National Park, South Africa. Prior to the drought, experimental fire frequencies (annual, triennial, and unburned) created savanna grassland plant communities that differed in composition and function, providing a unique opportunity to assess ecosystem resilience mechanisms under different fire regimes. Surprisingly, aboveground net primary productivity (ANPP) recovered fully in all fire frequencies the year after this exceptional drought. In burned sites, resilience was due mostly to annual forb ANPP compensating for reduced grass ANPP. In unburned sites, resilience of total and grass ANPP was due to subdominant annual and perennial grass species facilitating recovery in ANPP after mortality of other common grasses. This was possible because of high evenness among grass species in unburned sites predrought. These findings highlight the importance of both functional diversity and within‐functional group evenness as mechanisms of ecosystem resilience to extreme drought.
... C 4 plants evolved an augmentation to C 3 photosynthesis consisting of a biochemical CO 2 -concentrating mechanism. This mechanism concentrates CO 2 around Rubisco, allowing C 4 plants to operate at lower stomatal conductance (g S ) and transpiration (E), giving higher instantaneous photosynthetic water-use efficiency (WUE = A/E) compared with C 3 plants, particularly in Downloaded from https://academic.oup.com/aob/advance-article-abstract/doi/10.1093/aob/mcz048/5476057 by Library (Hancock) user on 01 May 2019 warm environments and under low [CO 2 ] a (Ward et al., 1999;Anderson et al., 2001;Seibt et al., 2008;Taylor et al., 2011;Cunniff et al., 2016). Selection pressure to reduce photorespiration under high evaporative demand and low [CO 2 ] a promoted the evolution of lineages that subsequently played a role in the expansion of C 4 -grass-dominated savannahs at the expense of closed woodland 8-10 Myr ago (Cerling et al., 1997;Edwards et al., 2010;Hoetzel et al., 2013). ...
Background and aims:
By the year 2100, atmospheric CO2 concentration ([CO2]a) could reach 800 ppm, having risen from ~200 ppm since the Neogene, beginning ~24 Myr ago. Changing [CO2]a affects plant carbon-water balance, with implications for growth, drought tolerance and vegetation shifts. The evolution of C4 photosynthesis improved plant hydraulic function under low [CO2]a and preluded the establishment of savannahs, characterized by rapid transitions between open C4-dominated grassland with scattered trees and closed forest. Understanding directional vegetation trends in response to environmental change will require modelling. But models are often parameterized with characteristics observed in plants under current climatic conditions, necessitating experimental quantification of the mechanistic underpinnings of plant acclimation to [CO2]a.
Methods:
We measured growth, photosynthesis and plant-water relations, within wetting-drying cycles, of a C3 tree (Vachellia karroo, an acacia) and a C4 grass (Eragrostis curvula) grown at 200, 400 or 800 ppm [CO2]a. We investigated the mechanistic linkages between trait responses to [CO2]a under moderate soil drying, and photosynthetic characteristics.
Key results:
For V. karroo, higher [CO2]a increased assimilation, foliar carbon:nitrogen, biomass and leaf starch, but decreased stomatal conductance and root starch. For Eragrostis, higher [CO2]a decreased C:N, did not affect assimilation, biomass or starch, and markedly decreased stomatal conductance. Together, this meant that C4 advantages in efficient water-use over the tree were maintained with rising [CO2]a.
Conclusions:
Acacia and Eragrostis acclimated differently to [CO2]a, with implications for their respective responses to water limitation and environmental change. Our findings question the carbon-centric focus on factors limiting assimilation with changing [CO2]a, how they are predicted and their role in determining productivity. We emphasize the continuing importance of water-conserving strategies in the assimilation response of savannah plants to rising [CO2]a.
... An enzyme, phosphoenolpyruvate carboxylase, is regulated by drought stress in the CAM pathway (Bayoumi et al., 2008;Said, 2014;Yoshida et al., 2014). Majority of crops in the Solanaceae family including S. aethiopicum group use the C3 photosynthetic pathway which predisposes the crop to excessive water loss (Ripley et al., 2007;Taylor et al., 2011). ...
Solanum aethiopicum is one of the most important Solanum species, with four morphological groups. Two of the groups, Gilo and Shum, are mainly cultivated because of their nutritional value and income generating potential for farmers in developing countries. Of focus for this study was the Shum, a leafy morphological group whose productivity and quality is directly affected by drought. Global limitations on water resource availability call for the need to develop productive varieties that are drought tolerant. This research was aimed at: (i) determining the genetic distinctiveness between Shum and its progenitor, S. anguivi (SAN); (ii) evaluating genetic diversity within Shum germplasm; (iii) identifying parental material for development of drought tolerant S. aethiopicum Shum varieties; and (iv) determining the combining ability of selected Shum group germplasm for drought tolerance. Twenty-five accessions, five of which were wild progenitors, were evaluated for morphological attributes. Similarly, clustering was used to identify structure within 20 accessions of Shum based on 61 morphological variables. Further, Shum germplasm were evaluated to discover accessions (G) which excelled across water deficit regimes (WLs) where a split-plot arrangement was used. In order to determine the mode of gene action and combining ability for drought resistance among accessions, 24 F1 hybrids from a North Carolina II mating design were evaluated at five moisture regimes premised on crop growth stage and applied moisture as a percentage of field capacity of potting substrate. Five distinct clusters were identified; the progenitor accessions for Shum were grouped in their own cluster; and days to germination and emergence provided the best separation between Shum and SAN. Four distinct clusters were obtained within Shum where it was established that genotype discrimination is possible at seedling (seedling vigor), vegetative (leaves per plant, harvest index and plant growth habit) and reproductive (for instance basing on petal length and seed color) stages. From drought screening study, highly significant effect (p < 0.05) of at least two WLs on performance among at least two genotypes for majority of the traits was obtained; in addition to very highly significant (p < 0.001) G x WL interactions for leaf relative water content (LRWC), leaves per plant (LPP) and plant height (PH). Basing on LRWC, superior and most stable genotypes were identified as E6 followed by E12, E15, E18 and E14GP. The broad sense heritability for each measured trait for water deficit stress tolerance breeding was > 0.9 and expected genetic advance as per cent of grand mean ranged from 16.68 (for LRWC) to 70.38 % (for PH) per generation; indicating a prospective response to selection. Effects of specific combining ability (SCA) were significant across and within moisture regimes for all traits studied unlike for general combining ability (GCA) where significant effects were obtained with chlorophyll content (CHL) only. In the narrow sense (h2), the most highly heritable traits were identified as LPP, CHL, leaf fresh yield (LYF) and leaf dry yield (LYD) while leaf area (LA), leaf mass area (LMA) and LRWC were least heritable. Broad sense heritability (H2) was however, > 0.80 for all measured traits, indicating that nonadditive gene action exceeded additive gene effects (VA) for moisture deficit stress tolerance in Shum. Female parent E11 had the best GCA effects for CHL. The crosses with best SCA effects were identified as E10xE20 (for LA under well-watered), E3HxE15 (for LYF across watering environments, LRWC under drought stress and CHL under drought recovery), and E11xE4 (for LMA under drought recovery). This research established that morphological markers are useful for distinguishing the Shum from its progenitor; as well as within Shum genotypes at any growth stage. Also, genotypes with good breeding value and promising specific crosses offer vital information as basis for establishment of a breeding programme for the crop.
Coastal wetland communities provide valuable ecosystem services such as erosion prevention, soil accretion, and essential habitat for coastal wildlife, but are some of the most vulnerable to the threats of climate change. This work investigates the combined effects of two climate stressors, elevated temperature (ambient, + 1.7 °C, + 3.4 °C, and 5.1 °C) and elevated CO 2 ( e CO 2 ), on leaf physiological traits of dominant salt marsh plant species. The research took place at the Salt Marsh Accretion Response to Temperature eXperiment (SMARTX) at the Smithsonian Environmental Research Center, which includes two plant communities: a C 3 sedge community and a C 4 grass community. Here we present data collected over five years on rates of stomatal conductance (g s ), quantum efficiency of PSII photochemistry ( F v / F m ), and rates of electron transport (ETR max ). We found that both warming and e CO 2 caused declines in all traits, but the warming effects were greater for the C 3 sedge. This species showed a strong negative stomatal response to warming in 2017 and 2018 (28% and 17% reduction, respectively in + 5.1 °C). However, in later years the negative response to warming was dampened to < 7%, indicating that S. americanus was able to partially acclimate to the warming over time. In 2022, we found that sedges growing in the combined + 5.1 °C e CO 2 plots exhibited more significant declines in g s , F v /F m , and ETR max than in either treatment individually. These results are important for predicting future trends in growth of wetland species, which serve as a large carbon sink that may help mitigate the effects of climate change.
Coastal wetland communities provide valuable ecosystem services such as erosion prevention, soil accretion, and essential habitat for coastal wildlife, but are some of the most vulnerable to the threats of climate change. This work investigates the combined effects of two climate stressors, elevated temperature (ambient, +1.7°C, +3.4°C, and 5.1 °C) and elevated CO2 (eCO2), on leaf physiological traits of dominant salt marsh plant species. The research took place at the Salt Marsh Accretion Response to Temperature eXperiment (SMARTX) at the Smithsonian Environmental Research Center, which includes two plant communities: a C3 sedge community and a C4 grass community. Here we present data collected over five years on rates of stomatal conductance (gs), quantum efficiency of PSII photochemistry (Fv/Fm), and rates of electron transport (ETRmax). We found that both warming and eCO2 caused declines in all traits, but the warming effects were greater for the C3 sedge. This species showed a strong negative stomatal response to warming in 2017 and 2018 (28% and 17% reduction, respectively in +5.1°C). However, in later years the negative response to warming was dampened to <7%, indicating that S. americanus was able to partially acclimate to the warming over time. In 2022, we found that sedges growing in the combined +5.1°C eCO2 plots exhibited more significant declines in gs, Fv/Fm, and ETRmax than in either treatment individually. These results are important for predicting future trends in growth of wetland species, which serve as a large carbon sink that may help mitigate the effects of climate change.
Fenlong-ridging (FL) is a new type of conservation tillage. In many crops, FL increases crop yield and quality; however, the cytology and molecular mechanisms of crops under FL is not completely understood. This study investigated soil physical and chemical properties under FL and conventional tillage (CK) during 2018–2019 (plant cane) and 2019–2022 (first stubble), and analyzed the agronomic trait, physiology, leaf anatomical structure, and gene expression related to photosynthesis between FL and CK of sugarcane (Guitang 42). Soil bulk density significantly increased, and soil porosity, water storage, and content of available nitrogen and phosphorus under FL were significantly higher than those under CK. Plant height, stem diameter, single stem weight, effective stem number and yield significantly increased under FL compared to under CK. Sugar content significantly increased in plant cane under FL. Chlorophyll content and the photosynthetic rate increased, with significantly higher activity of photosynthetic enzymes including NADP-malate dehydrogenase (NADP-MDH), phosphoenolpyruvate carboxylase (PEPC), and ribulose-1,5-bisphosphate carboxylase (RuBPC) under FL compared to CK. Fenlong-ridging cytology results showed that the mesophyll cells were large and arranged well, the Kranz anatomy was noticeable, and there were a high number of large chloroplasts in mesophyll cell and in the vascular bundle sheath. Furthermore, the bundle sheath in FL was larger than that in CK. Transcriptomics results showed that 19,357 differentially genes (DEGs) were up-regulated and 28,349 DEGs were down-regulated in sugarcane leaves under FL vs. CK. The Gene Ontology and Kyoto Encyclopedia of Genes and Genomes enrichment analysis revealed that abundant DEGs were enriched in photosynthesis, photosynthesis-antenna protein, carotenoid biosynthesis, and other pathways associated with photosynthesis. Most expression was up-regulated, thus, facilitating photosynthesis regulation. Quantitative real-time polymerase chain reaction analysis revealed the up-regulation of genes related to photosynthesis (PsaH and PsbS) under FL. Overall, this study provides insights into the role of FL in increased sugarcane yield by integrating physiology, cytology, and proteomics analysis. These findings could be used to further improve its application and promotion.
The world’s population has been increasing rapidly day by day and would demand more food from the limited natural resources such as land and water. Agricultural productivity will have to be increased substantially by using available resources, which are being depleted rapidly. Therefore, it is a challenging and herculean task for farming communities and agricultural technologists to fulfill the basic needs of the ever-increasing population. Agricultural scientists are engaged in developing improved varieties of crops along with their matching agro-technologies. Enhancing productivity and improving the quality of agricultural produce are the prime objectives of all the agricultural development organizations and funding agencies, and they are striving hard to achieve the same. Plant nutrients play a very important role in crop growth, development, and production. The role of phosphorus (P) in metabolic processes and potash (K) for inducing ability in plants is very significant to tolerate major abiotic and biotic stresses. These major crop nutrients are supplied traditionally through chemical fertilizers through soil irrigation, resulting in only 10–20% absorption by crop plants. The share of 80–90% of phosphate gets fixed in soil which is not available for the plants. To overcome these challenges on phosphorus and potash, the potassium salt of active phosphorus (PSAP) was invented using catalytic technology. The technical molecule of PSAP is 180% water-soluble and easily absorbed by the plant roots and leaves and plays a vital role in plant metabolism by inducing tolerance to the major biotic and abiotic stresses. Application of PSAP increases plant productivity from 30 to 50% with remarkable improvement in product quality along with the reduction in the cost of cultivation. The inclusion of PSAP in farming will certainly enhance the farmers’ income due to earning substantial additional profits. In conclusion, PSAP has emerged as a molecule of choice for enhancing the farmers’ income by improving the yield and quality and reducing the cost of crucial inputs.
Extreme environments, such as deserts and high-elevation ecosystems, are very important from biodiversity and ecological perspectives. However, plant physiology at those sites has been scarcely studied, likely due to logistic difficulties. In the present study, leaf physiological traits in native plants were analyzed from arid zones across an elevational transect in Western China, from Turpan Basin to the Qinghai-Tibet Plateau (QTP) at Delingha. The aim of this study was to use leaf physiological traits to help identifying potentially threatened species and true extremophiles. Physiological measurements in the field, and particularly in situ measurements of gas exchange and chlorophyll fluorescence, have been determined to be useful to determine the current state of plants at a given environment. Using this approach plus a combination of leaf traits, several species performing particularly well at the QTP were identified, e.g. Hedysarum multijugum, as well as at Manas drylands, e.g. Peganum harmala and Setaria viridis. On the other hand, several species showed marked signs of severe stress, in particular a very low photosynthetic rate over its potential maximum, as well as other negative traits, like low water and/or nitrogen-use-efficiency, which should be considered in conservation plans. Interestingly, all C4 species studied except Setaria viridis were among the most stressed species. Despite their higher water use efficiency and drought-tolerance reputation, they presented a much larger photosynthesis depression than most C3 species. This is an intriguing and interesting observation that deserves further studies.
Many aspects of early plant development are dependent on light exposure, but functional measures of chlorophyll development and chlorophyll fluorescence have not been conducted during a dark-to-light transition in seedlings. To study chlorophyll biosynthesis and overall photosynthetic activity development in leaves, seeds were germinated in darkness and etiolated leaves were then allowed to develop in lighted conditions. Zea mays (corn), Sorghum bicolor (sorghum), Vicia faba (broad bean), and Triticum aestivum (wheat) were investigated for the first eight days of sunlight exposure. Chlorophyll content and chlorophyll fluorescence measurements were conducted daily on the first true leaf on each plant. The first 5 days of the experiment, days 0 to 4 in light, had the greatest physiological impact on leaves of etiolated plants as they transitioned to a green state. Vicia faba and T. aestivum plants developed more chlorophyll and had faster rates of chlorophyll accumulation compared to Z. mays and S. bicolor plants. The majority of chlorophyll fluorescence parameters measured had less than a 20 percent change from days 4 to 8 in light. Chlorophyll fluorescence parameters in V. faba and Z. mays were higher than in T. aestivum and S. bicolor and took longer to reach a maximum value. Chlorophyll content and chlorophyll fluorescence had similar patterns of development, with consistent differences among species. This indicates that development of photosynthetic electron transport is related to chlorophyll content and likely differs based on leaf structure or other physiological factors.
Sufficient water and fertilizer inputs in agriculture play a major role in crop growth, production, and quality. In this study, the response of sugarcane to limited water irrigation and foliar application of potassium salt of active phosphorus (PSAP) for photosynthetic responses were examined, and PSAP's role in limited water irrigation management was assessed. Sugarcane plants were subjected to limited irrigation (95−90 and 45−40% FC) after three months of germination, followed by a foliar spray (0, 2, 4, 6, and 10 M) of PSAP. The obtained results indicated that limited water irrigation negatively affected sugarcane growth and reduced leaf gas exchange activities. However, the application of PSAP increased the photosynthetic activities by protecting the photosynthetic machinery during unfavorable conditions. Mathematical modeling, a Skewed model, was developed and compared with the existing Gaussian model to describe the photosynthetic responses of sugarcane leaves under the limited irrigation with and without PSAP application. The models fitted well with the observed values, and the predicted photosynthetic parameters were in close relationship with the obtained results. The Skewed model was found to be better than the Gaussian model in describing the photosynthetic parameters of plant leaves positioned over a stem of limited water irrigation and applied PSAP application and is recommended for further application.
Photosynthetic pathway is an important cause of growth rate variation between species such that the enhanced carbon uptake of C4 species leads to faster growth than their C3 counterparts. Leaf traits that promote rapid resource acquisition may further enhance the growth capacity of C4 species. However, how root economic traits interact with leaf traits, and the different growth strategies adopted by plants with C3 and C4 photosynthetic pathways is unclear. Plant economic traits could interact with, or act independently of, photosynthetic pathway in influencing growth rate, or C3 and C4 species could segregate out along a common growth rate–trait relationship.
We measured leaf and root traits on 100+ grass species grown from seeds in a controlled, common environment to compare with relative growth rates (RGR) during the initial phase of rapid growth, controlling for phylogeny and allometric effects.
Photosynthetic pathway acts independently to leaf and root functional traits in causing fast growth. Using C4 photosynthesis, plants can achieve faster growth than their C3 counterparts (by an average 0.04 g g⁻¹ day⁻¹) for a given suite of functional trait values, with lower investments of leaf and root nitrogen. Leaf and root traits had an additive effect on RGR, with plants achieving fast growth by possessing resource‐acquisitive leaf traits (high specific leaf area and low leaf dry matter content) or root traits (high specific root length and area, and low root diameter), but having both leads to an even faster growth rate (by up to 0.06 g g⁻¹ day⁻¹). C4 photosynthesis can provide a greater relative increase in RGR for plants with a ‘slow’ ecological strategy than in those with fast growth. However, above‐ground and below‐ground strategies are not coordinated so that species can have any combination of ‘slow’ or ‘fast’ leaf and root traits.
Synthesis. C4 photosynthesis increases growth rate for a given combination of economic traits, and significantly alters plant nitrogen economy in the leaves and roots. However, leaf and root economic traits act independently to further enhance growth. The fast growth of C4 grasses promotes a competitive advantage under hot, sunny conditions.
Since 1986, non-uniform photosynthesis over the leaf area that may be attributed to patchy stomatal closure, has been an important issue in stress physiology of photosynthesis. In this review, I first outline the gaseous environment within the intercellular spaces, because this is the most fundamental background of this problem. Then, recent studies approaching non-uniform photosynthesis are reviwed. After examining techniques for the detection of non-uniform photosynthesis or non-uniform stomatal aperture, results of the relevant studies are discussed for respective stress factors, seeking causes and consequences of non-uniform photosynthesis. From these, mechanisms responsible for, and consequences of non-uniform photosynthesis, are considered. The problems which should be challenged are also pointed out.
The global distribution of C3 and C4 plants is required for accurately simulating exchanges of CO2, water, and energy between the land surface and atmosphere. It is also important to know the C3/C4 distribution for simulations of the carbon isotope composition of atmospheric CO2 owing to the distinct fractionations displayed by each photosynthetic type. Large areas of the land surface are spatial and temporal mosaics of both photosynthetic types. We developed an approach for capturing this heterogeneity by combining remote sensing products, physiological modeling, a spatial distribution of global crop fractions, and national harvest area data for major crop types. Our C3/C4 distribution predicts the global coverage of C4 vegetation to be 18.8 million km2, while C3 vegetation covers 87.4 million km2. We incorporated our distribution into the SiB2 model and simulated carbon fluxes for each photosynthetic type. The gross primary production (GPP) of C4 plants is 35.3 Pg C yr-1, or ~23% of total GPP, while that of C3 plants is 114.7 Pg C yr-1. The assimilation-weighted terrestrial discrimination against 13CO2 is -16.50/00. If the terrestrial component of the carbon sink is proportional to GPP, this implies a net uptake of 2.4 Pg C yr-1 on land and 1.4 Pg C yr-1 in the ocean using a 13C budgeting approach and average carbon cycle parameter values for the 1990s. We also simulated the biomass of each photosynthetic type using the CASA model. The simulated biomass values of C3 and C4 vegetation are 389.3 and 18.6 Pg C, respectively.
C4 grasses constitute the main component of savannas and are pervasive in other dry tropical ecosystems where they serve as the main diet for grazing animals. Among potential factors driving C4 evolution of grasses, the interaction between grasses and grazers has not been investigated. To evaluate if increased grazing pressure may have selected for higher leaf silica production as the grasses diverged, we reconstructed the phylogeny of all 800 genera of the grass family with both molecular (combined multiplastid DNA regions) and morphological characters. Using molecular clocks, we also calculated the age and number of origins of C4 clades and found that shifts from C3 to C4 photosynthesis occurred at least 12 times starting 30.9 million years ago and found evidence that the most severe drop in atmospheric carbon dioxide in the late Oligocene (between 33 and 30 million years ago) matches the first origin of C4 photosynthesis in Chloridoideae. By combining fossil and phylogenetic data for ungulates and implementing a randomization procedure, our results showed that the appearance of C4 grass clades and ungulate adaptations to C4-dominated habitats match significantly in time. An increase of leaf epidermal density of silica bodies was found to correspond to postulated shifts in diversification rates in the late Miocene [24 significant shifts in diversification (P<0.05) were detected between 23 and 3.7 million years ago]. For aristidoid and chloridoid grasses, increased grazing pressure may have selected for a higher leaf epidermal silica production in the late Miocene.
Living cells need to be more or less saturated with water to function normally, but they are usually incomplete in this desirable condition. The two basic parameters which describe the degree of unsaturation, i.e. the plant water deficit are (i) the water content and (ii) the energy status of the water in the cell. The water content is usually expressed as relative to that at full saturation, i.e. the relative water content or water saturation deficit, and the energy status of the water is usually expressed as the total water protential. Although the two parameters are linked in such a way that the total water potential decreases as the water content decreases, the relationship between the two, variously known as the moisture release curve, water potential isotherm or water retention characteristic, is not unique but varies with species, growth conditions and stress history (Slatyer, 1960; Jarvis and Jarvis, 1963; Altmann and Dittmer, 1966; Noy Meir and Ginzburg, 1969; Ludlow, 1976; Jones and Turner, 1978). Thus for completeness, both the water content and energy status of the water in plant tissue need to be measured. The total water potential (7') at any point in the plant can be partitioned into its components: the osmotic potential (re), turgor pressure (P), matric potential (z) and gravitational potential. As the gravitational component of the total water potential is only 0.01 MPa m- 1 (0.1 MPa = 1 bar), it can be neglected, except in very tall trees (Conner et al., 1977). For cells in equilibrium with their surroundings the total water potential is the same throughout the system, i.e. in the wall, cytoplasm, organelles and vacuole. However, the components of the total water potential may be quite different: in the vacuole the total water potential arises largely from osmotic and turgor forces, whereas in the wall, it arises largely from matric forces and to a small degree from osmotic forces. Thus the total water potential of a plant cell is given
At high temperatures and relatively low CO2 concentrations, plants can most efficiently fix carbon to form carbohydrates through C4 photosynthesis rather than through the ancestral and more widespread C3 pathway. Because most C4 plants are grasses, studies of the origin of C4 are intimately tied to studies of the origin of the grasses. We present here a phylogeny of the grass family, based on nuclear and chloroplast genes, and calibrated with six fossils. We find that the earliest origins of C4 likely occurred about 32 million years ago (Ma) in the Oligocene, coinciding with a reduction in global CO2 levels. After the initial appearance of C4 species, photosynthetic pathway changed at least 15 more times; we estimate nine total origins of C4 from C3 ancestors, at least two changes of C4 subtype, and five reversals to C3. We find a cluster of C4 to C3 reversals in the Early Miocene correlating with a drop in global temperatures, and a subsequent cluster of C4 origins in the Mid-Miocene, correlating with the rise in temperature at the Mid-Miocene climatic optimum. In the process of dating the origins of C4, we were also able to provide estimated times for other major events in grass evolution. We find that the common ancestor of the grasses (the crown node) originated in the upper Cretaceous. The common ancestor of maize and rice lived at 52 ± 8 Ma.
The success of C4 plants lies in their ability to attain greater efficiencies of light, water and nitrogen use under high temperature, providing an advantage in arid, hot environments. However, C4 grasses are not necessarily less sensitive to drought than C3 grasses and are proposed to respond with greater metabolic limitations, while the C3 response is predominantly stomatal. The aims of this study were to compare the drought and recovery responses of co-occurring C3 and C4 NADP-ME grasses from the subfamily Panicoideae and to determine stomatal and metabolic contributions to the observed response.
Six species of locally co-occurring grasses, C3) species Alloteropsis semialata subsp. eckloniana, Panicum aequinerve and Panicum ecklonii, and C4 (NADP-ME) species Heteropogon contortus, Themeda triandra and Tristachya leucothrix, were established in pots then subjected to a controlled drought followed by re-watering. Water potentials, leaf gas exchange and the response of photosynthetic rate to internal CO2 concentrations were determined on selected occasions during the drought and re-watering treatments and compared between species and photosynthetic types.
Leaves of C4 species of grasses maintained their photosynthetic advantage until water deficits became severe, but lost their water-use advantage even under conditions of mild drought. Declining C4 photosynthesis with water deficit was mainly a consequence of metabolic limitations to CO2 assimilation, whereas, in the C3 species, stomatal limitations had a prevailing role in the drought-induced decrease in photosynthesis. The drought-sensitive metabolism of the C4 plants could explain the observed slower recovery of photosynthesis on re-watering, in comparison with C3 plants which recovered a greater proportion of photosynthesis through increased stomatal conductance.
Within the Panicoid grasses, C4 (NADP-ME) species are metabolically more sensitive to drought than C3 species and recover more slowly from drought.
The effects of abscisic acid (ABA) on photosynthesis in leaves of Helianthus annuus L. were compared with those in leaves of Vicia faba L. After the ABA treatment, the response of photosynthetic CO2 assimilation rate, A, to calculated intercellular partial pressure of CO2, Pi, (A(pi) relationship) was markedly depressed in H. annuus. A less marked depression was also observed in V.faba. However, when the abaxial epidermes were removed from these leaves, neither the maximum rate nor the CO2 response of photosynthetic oxygen evolution was affected by the application of ABA.
Starch-iodine tests revealed that photosynthesis was not uniform over the leaves of H. annuus treated with ABA. The starch content was diffferent in each bundle sheath extension compartment (the smallest subdivision of mesophyll by veins with bundle sheath extensions, having an area of ca. 0.25 mm² and ca. 50 stomata). In some compartments, no starch was detected. The distribution of open stomata, examined using the silicone rubber impression techniques, was similar to the pattern of starch accumulation. In V.faba leaves, which lack bundle sheath extensions, distribution of starch was more homogeneous.
These results indicate that the apparent non-stomatal inhibition of photosynthesis by ABA deduced from the depression of A(pⁱ) relationship is an artifact which can be attributed to the non-uniform distribution of transpiration and photosynthesis over the leaf. Intercellular gaseous environment in the ABA-treated leaves is discussed in relation to mesophyll anatomy.
Grasses using the C(4) photosynthetic pathway dominate grasslands and savannahs of warm regions, and account for half of the species in this ecologically and economically important plant family. The C(4) pathway increases the potential for high rates of photosynthesis, particularly at high irradiance, and raises water-use efficiency compared with the C(3) type. It is therefore classically viewed as an adaptation to open, arid conditions. Here, we test this adaptive hypothesis using the comparative method, analysing habitat data for 117 genera of grasses, representing 15 C(4) lineages. The evidence from our three complementary analyses is consistent with the hypothesis that evolutionary selection for C(4) photosynthesis requires open environments, but we find an equal likelihood of C(4) evolutionary origins in mesic, arid and saline habitats. However, once the pathway has arisen, evolutionary transitions into arid habitats occur at higher rates in C(4) than C(3) clades. Extant C(4) genera therefore occupy a wider range of drier habitats than their C(3) counterparts because the C(4) pathway represents a pre-adaptation to arid conditions. Our analyses warn against evolutionary inferences based solely upon the high occurrence of extant C(4) species in dry habitats, and provide a novel interpretation of this classic ecological association.
I compared the C(4) grass flora and climatic records for 32 sites in the United States. Consistent with previous studies, I found that the proportion of the grass flora that uses the NADP malic enzyme (NADP-ME) variant of C(4) photosynthesis greatly increases with increasing annual precipitation, while the proportion using the NAD malic enzyme (NAD-ME) variant (and also the less common phosphoenolpyruvate carboxykinase [PCK] variant) decreases. However the association of grass subfamilies with annual precipitation was even stronger than for the C(4) decarboxylation variants. Analysis of the patterns of distribution by partial correlation analysis showed that the correlations between the frequency of various C(4) types and rainfall were solely due to the association of the C(4) types with particular grass subfamilies. In contrast, there was a strong correlation of the frequency of the different subfamilies with annual precipitation that was independent of the influence of the different C(4) variants. It therefore appears that other, as yet unidentified, characteristics that differ among grass subfamilies may be responsible for their differences in distribution across natural precipitation gradients.
Experimental studies on CO2 assimilation of mesophytic C3 plants in relation to relative water content (RWC) are discussed. Decreasing RWC slows the actual rate of photosynthetic CO2 assimilation (A) and decreases the potential rate (Apot). Generally, as RWC falls from c. 100 to c. 75%, the stomatal conductance (gs) decreases, and with it A. However, there are two general types of relation of Apot to RWC, which are called Type 1 and Type 2. Type 1 has two main phases. As RWC decreases from 100 to c. 75%, Apot is unaffected, but decreasing stomatal conductance (gs) results in smaller A, and lower CO2 concentration inside the leaf (Ci) and in the chloroplast (Cc), the latter falling possibly to the compensation point. Down-regulation of electron transport occurs by energy quenching mechanisms, and changes in carbohydrate and nitrogen metabolism are considered acclimatory, caused by low Ci and reversible by elevated CO2. Below 75% RWC, there is metabolic inhibition of Apot, inhibition of A then being partly (but progressively less) reversible by elevated CO2; gs regulates A progressively less, and Ci and CO2 compensation point, Gamma rise. It is suggested that this is the true stress phase, where the decrease in Apot is caused by decreased ATP synthesis and a consequent decreased synthesis of RuBP. In the Type 2 response, Apot decreases progressively at RWC 100 to 75%, with A being progressively less restored to the unstressed value by elevated CO2. Decreased gs leads to a lower Ci and Cc but they probably do not reach compensation point: gs becomes progressively less important and metabolic limitations more important as RWC falls. The primary effect of low RWC on Apot is most probably caused by limited RuBP synthesis, as a result of decreased ATP synthesis, either through inhibition of Coupling Factor activity or amount due to increased ion concentration. Carbohydrate synthesis and accumulation decrease. Type 2 response is considered equivalent to Type 1 at RWC below c. 75%, with Apot inhibited by limited ATP and RuBP synthesis, respiratory metabolism dominates and Ci and Gamma rise. The importance of inhibited ATP synthesis as a primary cause of decreasing Apot is discussed. Factors determining the Type 1 and Type 2 responses are unknown. Electron transport is maintained (but down-regulated) in Types 1 and 2 over a wide range of RWC, and a large reduced/oxidized adenylate ratio results. Metabolic imbalance results in amino acid accumulation and decreased and altered protein synthesis. These conditions profoundly affect cell functions and ultimately cause cell death. Type 1 and 2 responses may reflect differences in gs and in sensitivity of metabolism to decreasing RWC.
Cuticular properties affect the gas exchange of leaves, but little is known about how much CO2 and water vapor cross the cuticular barrier or whether low water potentials affect the process. Therefore, we measured the cuticular conductances for CO2 and water vapor in grape (Vitis vinifera L.) leaves having various water potentials. The lower leaf surface was sealed to force all gas exchange through the upper surface, which was stoma-free. In this condition both gases passed through the cuticle, and the CO2 conductance could be directly determined from the internal mole fraction of CO2 near the compensation point, the external mole fraction of CO2, and the CO2 flux. The cuticle allowed small amounts of CO2 and water vapor to pass through, indicating that gas exchange occurs in grape leaves no matter how tightly the stomata are closed. However, the CO2 conductance was only 5.7% of that for water vapor. This discrimination against CO2 markedly affected calculations of the mole fraction of CO2 in leaves as stomatal apertures decreased. When the leaf dehydrated, the cuticular conductance to water vapor decreased, and transpiration and assimilation diminished. This dehydration effect was largest when turgor decreased, which suggests that cuticular gas exchange may have been influenced by epidermal stretching.
Nine conifer species with narrow (<5 mm), single-veined leaves were selected for the purpose of examining changes in intercellular CO2 concentration (ci) during drought. Due to the leaf morphology of the study plants, the confounding effects of nonhomogenous photosynthesis common to most reticulate-veined angiosperms were largely avoided, giving a clear picture of ci dynamics under increasing drought. A characteristic biphasic response was observed in all species, with an initial stomatal control phase resulting in a substantial reduction in ci as stomatal conductance (gs) decreased. As gs reached low levels, a strong nonstomatal limitation phase was observed, causing ci to increase as gs approached a minimum. This nonstomatal phase was linked to a concomitant rapid decrease in the fluorescence parameter quantum efficiency, indicating the onset of nonreversible photoinhibition. The ratio of internal to atmospheric CO2 concentration (ci/ca) decreased from values of between 0.68 and 0.57 in undroughted plants to a minimum, (ci/ca)min, which was well defined in each species, ranging from 0.10 in Actinostrobus acuminatus to 0.36 in Acmopyle pancheri. A high correlation was found to exist between (ci/ca)min and leaf water potential measured at (ci/ca)min. Species developing high maximum intrinsic water use efficiencies (low [ci/ca]min), such as A. acuminatus, did so at lower leaf water potentials (-4.5 MPa) than more mesic species (-1.75 MPa for A. pancheri). It is concluded that in the absence of patchy stomatal closure, (ci/ca)min gives a good representation of the drought tolerance of foliage.
Observations of nonuniform photosynthesis across leaves cast doubt on internal CO(2) partial pressures (p(i)) calculated on the assumption of uniformity and can lead to incorrect conclusions about the stomatal control of photosynthesis. The problem can be avoided by measuring p(i) directly because the assumptions of uniformity are not necessary. We therefore developed a method that allowed p(i) to be measured continuously in situ for days at a time under growth conditions and used it to investigate intact leaves of sunflower (Helianthus annuus L.), soybean (Glycine max L. Merr.), and bush bean (Phaseolus vulgaris L.) subjected to high or low leaf water potentials (psi(w)) or high concentrations of abscisic acid (ABA). The leaves maintained a relatively constant differential (Deltap) between ambient CO(2) and measured p(i) throughout the light period when water was supplied. When water was withheld, psi(w) decreased and the stomata began to close, but measured p(i) increased until the leaf reached a psi(w) of -1.76 (bush bean), -2.12 (sunflower) or -3.10 (soybean) megapascals, at which point Deltap = 0. The increasing p(i) indicated that stomata did not inhibit CO(2) uptake and a Deltap of zero indicated that CO(2) uptake became zero despite the high availability of CO(2) inside the leaf. In contrast, when sunflower leaves at high psi(w) were treated with ABA, p(i) did not increase and instead decreased rapidly and steadily for up to 8 hours even as psi(w) increased, as expected if ABA treatment primarily affected stomatal conductance. The accumulating CO(2) at low psi(w) and contrasting response to ABA indicates that photosynthetic biochemistry limited photosynthesis at low psi(w) but not at high ABA.
Isohydric and anisohydric regulations of plant water status have been observed over several decades of field, glasshouse and laboratory studies, yet the functional significance and mechanism of both remain obscure. We studied the seasonal trends in plant water status and hydraulic properties in a natural stand of Eucalyptus gomphocephala through cycles of varying environmental moisture (rainfall, groundwater depth, evaporative demand) in order to test for isohydry and to provide physiological information for the mechanistic interpretation of seasonal trends in plant water status. Over a 16 month period of monitoring, spanning two summers, midday leaf water potential (psi(leaf)) correlated with predawn psi(leaf), which was correlated with water table depth below ground level, which in turn was correlated with total monthly rainfall. Eucalyptus gomphocephala was therefore not seasonally isohydric. Despite strong stomatal down-regulation of transpiration rate in response to increasing evaporative demand, this was insufficient to prevent midday psi(leaf) from falling to levels below -2 MPa in the driest month, well into the region likely to induce xylem air embolisms, based on xylem vulnerability curves obtained in the study. However, even though midday psi(leaf) varied by over 1.2 MPa across seasons, the hydrodynamic (transpiration-induced) water potential gradient from roots to shoots (delta psi(plant)), measured as the difference between predawn and midday psi(leaf), was relatively constant across seasons, averaging 0.67 MPa. This unusual pattern of hydraulic regulation, referred to here as isohydrodynamic, is explained by a hydromechanical stomatal control model where plant hydraulic conductance is dependent on transpiration rate.
Phylogenetic thinking has infiltrated many areas of biological research, but has had little impact on studies of global ecology or climate change. Here, we illustrate how phylogenetic information can be relevant to understanding vegetation-atmosphere dynamics at ecosystem or global scales by re-analyzing a data set of carbonic anhydrase (CA) activity in leaves that was used to estimate terrestrial gross primary productivity. The original calculations relied on what appeared to be low CA activity exclusively in C4 grasses, but our analyses indicate that such activity might instead characterize the PACCAD grass lineage, which includes many widespread C3 species. We outline how phylogenetics can guide better taxon sampling of key physiological traits, and discuss how the emerging field of phyloinformatics presents a promising new framework for scaling from organism physiology to global processes.
The C4 photosynthetic pathway uses water more efficiently than the C3 type, yet biogeographical analyses show a decline in C4 species relative to C3 species with decreasing rainfall. To investigate this paradox, the hypothesis that the C4 advantage over C3 photosynthesis is diminished by drought was tested, and the underlying stomatal and metabolic mechanisms of this response
determined. The effects of drought and high evaporative demand on leaf gas exchange and photosynthetic electron sinks in C3 and C4 subspecies of the grass Alloteropsis semialata were examined. Plant responses to climatic variation and soil drought were investigated using a common garden experiment
with well-watered and natural rainfall treatments, and underlying mechanisms analysed using controlled drying pot experiments.
Photosynthetic rates were significantly higher in the C4 than the C3 subspecies in the garden experiment under well-watered conditions, but this advantage was completely lost during a rainless
period when unwatered plants experienced severe drought. Controlled drying experiments showed that this loss was caused by
a greater increase in metabolic, rather than stomatal, limitations in C4 than in the C3 leaves. Decreases in CO2 assimilation resulted in lower electron transport rates and decreased photochemical efficiency under drought conditions,
rather than increased electron transport to alternative sinks. These findings suggest that the high metabolic sensitivity
of photosynthesis to severe drought seen previously in several C4 grass species may be an inherent characteristic of the C4 pathway. The mechanism may explain the paradox of why C4 species decline in arid environments despite high water-use efficiency.
The discipline of environmental biophysics relates to the study of energy and mass exchange between living organisms and their environment. The study of environmental biophysics probably began earlier than that of any other science, since knowledge of organism-environment interaction provided a key to survival and progress. Systematic study of the science and recording of experimental results, however, goes back only a few hundred years. Recognition of environmental biophysics as a discipline has occurred just within the past few decades.
R package for Data Analysis using multilevel/hierarchical model
Anatomical and morphological structures of leaf blades were compared between C3 and C4 species in Panicum. Inter-specific variation of stomatal density, longitudinal vein density and mesophyll thickness was highly correlative either plus or minus within respective groups. The two groups could not be distinguished by a single character, since the variation ranges overlapped each other. However, the quantitative relations between vein density and the other two characters differentiated the two groups well. In C3, stomatal density seemed to be a primary factor for regulating water balance, while in C4 vein system was considered to be important for the regulation. The species with intermediate photosynthesis behaved similar to the C3 species. In the C3 group, correlative variation was observed between leaf width, leaf angle and the three characters mentioned above. Variation of light-receiving area due to the changes of width and angle of leaf blades was considered to be one of the adaptive strategies of this group. Increase of light-receiving area was in connection with the thinning of leaves. On the other hand, in the C4 correlations between length, width and angle of leaves were low. Such loose character correlation may be achieved by its efficiency of CO2 utilization and its well developed vein systems. Besides, NAD-me type species tended to have relatively lower stomatal and vein densities as compared with the other decarboxylation types in this group.
Experimental evidence demonstrates a higher efficiency of water and nitrogen use in C 4 compared with C 3 plants, which is hypothesized to drive differences in biomass allocation between C 3 and C 4 species. However, recent work shows that contrasts between C 3 and C 4 grasses may be misinterpreted without phylogenetic control. • Here, we compared leaf physiology and growth in multiple lineages of C 3 and C 4 grasses sampled from a monophyletic clade, and asked the following question: which ecophysiological traits differ consistently between photosynthetic types, and which vary among lineages? • C 4 species had lower stomatal conductance and water potential deficits, and higher water-use efficiency than C 3 species. Photosynthesis and nitrogen-use efficiency were also greater in C 4 species, varying markedly between clades. Contrary to previous studies, leaf nitrogen concentration was similar in C 4 and C 3 types. Canopy mass and area were greater, and root mass smaller, in the tribe Paniceae than in most other lineages. The size of this phylogenetic effect on biomass partitioning was greater in the C 4 NADP-me species than in species of other types. • Our results show that the phylogenetic diversity underlying C 4 photosynthesis is critical to understanding its functional consequences. Phylogenetic bias is therefore a crucial factor to be considered when comparing the ecophysiology of C 3 and C 4 species.
The functional significance of different photosynthetic CO2 fixation pathways is a question which can be answered in many ways, each being appropriate to certain scales of enquiry. In physiological ecology our purpose should be to integrate these different scales of enquiry as comprehensively as possible, and to show how photosynthesis contributes, directly or indirectly, to performance and survival of plants in diverse habitats. Studies of photosynthetic CO2 fixation were afflicted with a post-Calvin cycle chauvinism in the 1950’s, which may have been responsible for the slow and tentative revelation of the C4 pathway of photosynthetic carbon assimilation in the USA and USSR (Burr et al. 1957; Karpilov 1960; Kortschak et al. 1965). Elucidation of this pathway undoubtedly stimulated new interest in the carbon metabolism of photosynthesis in the next decade (Hatch and Slack 1966, 1970; CC Black 1973) and led to an upsurge in comparative studies of higher plant photosynthesis (Black 1971; Björkman 1973). Largely as a result of this stimulus, the peculiar dark CO2 fixation processes of succulent plants, known as crassulacean acid metabolism (CAM), were also recognized as a distinctive photosynthetic process (Kluge and Ting 1978; Osmond 1978). It also led to the present revival of interest in the photosynthesis of aquatic plants.
