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Physiological responses in two populations of Andropogon glomeratus Walter B.S.P. to short-term salinity
Abstract
Andropogon glomeratus is a C4 nonhalophytic grass which exhibits population differentiation for tolerance to short-term salinity exposure. To investigate possible physiological mechanisms whch enable salt-tolerant individuals to survive short-term inundation, gas exchange and water relations parameters were measured before and during a 5-day watering treatment of half-strength synthetic seawater in plants from a tolerant and a non-tolerant population. Photosynthetic recovery was followed for 10 days after the salinity treatment. Photosynthetic CO2 uptake was substantially inhibited in both populations. Stomatal conductances decreased and intercellular CO2 concentrations increased, indicating non-stomatal factors were primarily responsible for the decrease in CO2 uptake. After termination of the salinity treatment photosynthetic capacity increased more rapidly in the tolerant population and reached the pretreatment level after 6 days, whereas the nontolerant population did not recover fully after 10 days. A-Ci curves measured before and after the salinity treatment indicated a decrease in the carboxylation efficiency, and suggested a proportionately greater metabolic inhibition relative to the increase in the stomatal limitation. Osmotic adjustment occurred in a 2-day period in the tolerant population, but there was no change in the osmotic potentials or the water potential at the point of turgor loss in the nontolerant population. Thus short-term salt tolerance in the marsh population is associated with rapid osmotic adjustment and recovcry of photosynthetic capacity shortly after the end of the salinity exposure, rather than maintenance of greater photosynthesis during the salinity treatment.
... In coastal sandy habitats, the proximity to the coast and the seasonal distribution of rainfall result in pronounced variation in soil salinity and fresh water availability. Substrates continuously receive high levels of salt from aerosol spray and oceanic waters, and typically experience salinities oscillating from fresh to seawater (Bowman and Strain, 1988;Howard and Mendelssohn, 1999;Jefferies et al., 1979;Omer and Barclay, 2002). In this environment, a range of higher plants with contrasting ecophysiological properties co-exist and are often classified as halophytes or non-halophytes with different levels of salt tolerance. ...
... In species that experience abrupt increases in soil salinity, selection probably has acted upon physiological traits that favor tolerance to rapidly imposed salinity. These probably include rapid osmotic adjustment and recovery of photosynthetic capacity following tidal inundation (Akhiyarova et al., 2005;Bowman and Strain, 1988;Flowers et al., 1986). In some salt marsh and crop species, this adjustment to seawater salinity can be achieved in 24-48 h (Akhiyarova et al., 2005;Bowman and Strain, 1988;Flowers et al., 1986;McNulty, 1985;Murphy et al., 2003). ...
... These probably include rapid osmotic adjustment and recovery of photosynthetic capacity following tidal inundation (Akhiyarova et al., 2005;Bowman and Strain, 1988;Flowers et al., 1986). In some salt marsh and crop species, this adjustment to seawater salinity can be achieved in 24-48 h (Akhiyarova et al., 2005;Bowman and Strain, 1988;Flowers et al., 1986;McNulty, 1985;Murphy et al., 2003). Fast osmotic adjustments require ion accumulation up to a concentration equal to or greater than that of the surrounding root solution in order to achieve an osmotic gradient for the uptake of soil water (Flowers et al., 1986;Greenway and Munns, 1980;Naidoo and Rughunanan, 1990). ...
Ipomoea pes-caprae is widespread in pantropical coastal areas along the beach. The aim of this study was to investigate the salinity tolerance level and physiological mechanisms that allow I. pes-caprae to endure abrupt increases in salinity under brief or prolonged exposure to salinity variations. Xylem sap osmolality (Xosm), leaf water relations, gas exchange, and number of produced and dead leaves were measured at short- (1–7d) and long- (22–46d) term after a sudden increase in soil salinity of 0, 85, 170, and 255mM NaCl. In the short-term, Xosm was not affected by salinity, but in the long-term there was a significant increase in plants grown in presence of salt compared with control plants. After salt addition, the plants showed osmotic stress with temporal cell turgor loss. However, the water potential gradient for water uptake was re-established at 4, 7 and 22d after salt addition, at 85, 170 and 255mM NaCl, respectively. In the short-term I. pes-caprae was able to tolerate salinities of up to 255mM NaCl without significant reduction in carbon assimilation or growth. With the duration of stress, leaf ion concentration continued to increase and reached toxic levels at high salinity with a progressive decrease in photosynthetic rate, reduced leaf formation and accelerated senescence. Then, if high levels of soil salts from tidal inundation occur for short periods, the survival of I. pes-caprae is possible, but prolonged exposure to salinity may induce metabolic damage and reduce drastically the plant growth.
... For example, there was a significant positive correlation between lower canopy temperature and higher yield under conditions of high temperature and drought . The stomatal conductance decreased and the leaf temperature increased with stoma closure under osmotic stress caused by excess salinity and high temperature, which can be used to estimate leaf water potential and stomatal conductance (Bowman and Strain, 1988;Wang et al., 2003). ...
Phenotyping plays an important role in crop science research; the accurate and rapid acquisition of phenotypic information of plants or cells in different environments is helpful for exploring the inheritance and expression patterns of the genome to determine the association of genomic and phenotypic information to increase the crop yield. Traditional methods for acquiring crop traits, such as plant height, leaf color, leaf area index (LAI), chlorophyll content, biomass and yield, rely on manual sampling, which is time-consuming and laborious. Unmanned aerial vehicle remote sensing platforms (UAV-RSPs) equipped with different sensors have recently become an important approach for fast and non-destructive high throughput phenotyping and have the advantage of flexible and convenient operation, on-demand access to data and high spatial resolution. UAV-RSPs are a powerful tool for studying phenomics and genomics. As the methods and applications for field phenotyping using UAVs to users who willing to derive phenotypic parameters from large fields and tests with the minimum effort on field work and getting highly reliable results are necessary, the current status and perspectives on the topic of UAV-RSPs for field-based phenotyping were reviewed based on the literature survey of crop phenotyping using UAV-RSPs in the Web of Science™ Core Collection database and cases study by NERCITA. The reference for the selection of UAV platforms and remote sensing sensors, the commonly adopted methods and typical applications for analyzing phenotypic traits by UAV-RSPs, and the challenge for crop phenotyping by UAV-RSPs were considered. The review can provide theoretical and technical support to promote the applications of UAV-RSPs for crop phenotyping.
... The evaluation of crop varieties resilient to salinity and heat stress can also be assessed efficiently using UAV-based sensing. In the case of salinity and heat stress, osmotic stress leads to stomatal closure, decreased stomatal conductance, increased leaf temperature (Bowman and Strain, 1988;Wang et al., 2003;Microbes, 2015), and decreased photosynthesis. These changes in photosynthetic rates and stomatal conductance can be detected by visible to near-infrared spectral reflectance (Stong, 2008). ...
... As Bethenod and Tardieu (1990) have noted, the slope of this relationship is equal to C a -C i (from Eq. (3)), and thus, linearity implies a constant C i. Wong et al. (1985a,b) also demonstrated C i to be nearly constant over a wide range of Pn~t in both C3 and C4 plants, even when influenced by nitrogen and phosphorous nutrition, by water stress (see also Di Marco et al., 1988) and by photoinhibition. Constant Ci has also been reported through variations in salinity (Bowman and Strain 1988) and midday stomatal closure (Tenhunen et al. 1984, Barthou et al. 1988, and independent of leaf temperature or v.p.d, effects on conductance (Andrews and Muller 1985). ...
In this report, we analyze the photosynthetic capacity and performance of leaves under field conditions with a case study based on the mangroves Bruguiera parviflora and B. gymnorrhiza. Using a tower through a closed canopy at a field sight in North Queensland and portable infra-red gas analyzers, a large data set was collected over a period of 11 days early in the growing season. The set was used to analyze the relationship between net photosynthesis (Pnet) and light, leaf temperature, stomatal conductance and intracellular CO2 (Ci).There are three objectives of this report: (1) to determine photosynthetic potential as indicated by the in situ responses of Pnet to light and stomatal conductance, (2) to determine the extent to which photosynthetic performance may be reduced from that potential, and (3) to explore the basis for and physiological significance of the reduction.The results indicate that even under harsh tropical conditions, the mangrove photosynthetic machinery is capable of operating efficiently at low light and with maximal rates of more than 15 mol CO2 m-2 s-1. Though stomata were more often limiting than light, in any single measurement the average reduction of Pnet from the maximum value predicted by light or conductance responses was 35%. Analysis of single leaf light and CO2 responses indicated that photosynthetic performance was under direct photosynthetic, or non-stomatal, control at all light and conductance levels. Capacity was adjustable rapidly from a maximum value to essentially nil such that Ci varied inversely with Pnet from ca. 150 L L-1 at the highest rates of CO2 exchange to ambient at the lowest.
... In our experiment, a massive accumulation of salt occurred only in leaves of plants in the 240 and 320 mM salt treatments: it affected the recovery rate (de Herralde et al. 1998) but did not influence long-term photosynthetic performance ( Figure 2). These results may have ecological significance, because fast recovery of photosynthesis strongly determines the overall salt tolerance of species under natural conditions (Bowman and Strain 1988). ...
Leaf gas exchange, water relations and osmotic adjustment were studied in hydroponically grown Phillyrea latifolia L. plants exposed to 5 weeks of salinity stress (0, 80, 160, 240 and 320 mM NaCl) followed by 5 weeks of treatment with half-strength Hoagland solution. Whole-plant relative growth rate and root/shoot and lateral/structural root ratios were also evaluated. Net CO2 assimilation rate, stomatal conductance and transpiration rate were markedly decreased by all of the salt treatments. Growth was also strongly depressed by all salt treatments, especially lateral root growth. Leaf water potential decreased soon after salinity stress was imposed, whereas there was a lag of several weeks before leaf osmotic potential decreased in response to the salt treatments. After 5 weeks of salinization, leaf turgor of salt-treated plants was similar to that of controls. Although Na+ + Cl- contributed little to the salt-induced changes in osmotic potential at full turgor (Psi(piFT)), the contributions of K+, mannitol (Man) and glucose (Glc) to Psi(piFT) markedly increased as external salinity increased. Salt accumulation was negligible in the youngest leaves, which mostly accumulated soluble carbohydrates and K+; in contrast, old leaves served as storage sinks for Na+ and Cl-. Photosynthetic performance of salt-treated plants fully recovered once salt was leached from the root zone, with the recovery rate depending on the severity of the salt stress previously experienced by the plants. Recovery of gas exchange occurred even though the leaves still had a salt load similar to that detected in leaves at the end of the 5-week salinity period, and had markedly lower concentrations of K+ and soluble carbohydrates than control leaves. We conclude that salt-induced water stress primarily controlled gas exchange of salt-treated P. latifolia leaves, whereas the salt load in the leaves did not cause irreversible damage to the photosynthetic apparatus.
The influence of estuarine waters and rainfall deficit on top soil (0–5 cm) salinity was investigated for 23 stations situated along an intertidal gradient sampled at monthly intervals over a 4-year period. Up to a level half-way between MSL (mean sea level) and MHW (mean high water) soil salinity was strongly correlated with fluctuations in inundation water salinity. On average, 80% of the variation could be explained by this single factor. The impact of the estuarine waters on sediment salinity decreased above this level and dropped below significance level at 58 cm above MHW. The correlation between the rainfall deficit over the 5 days prior to soil sampling and soil salinity was significant at site elevations of 4 cm below MHW and higher. These results suggest that functioning of salt marsh ecosystems occurring below MHW will not be affected by precipitation or drought.
This research was undertaken to investigate differences in salt tolerance under conditions in which salinity is increased gradually and maintained for long periods or increased rapidly and maintained for shorter periods. The responses of populations of a C4 nonhalophytic grass, Andropogon glomeratus, to long- and short-term salinity were measured under controlled environment conditions. Additionally, plants from a salt marsh population and an inland population were transplanted into a salt marsh and their survival compared. The relative growth reductions in the salt marsh and the inland populations under long-term salinity were similar. Survival of seedlings of 4 populations inundated with full-strength seawater over a relatively short period indicated differential capacities to tolerate soil salinities imposed in a manner similar to tidal inundation in a salt marsh. The greater survival of plants from the marsh population transplanted into the salt marsh further indicated genetic differentiation between the populations. These results indicate that genetic differentiation to salt tolerance in A. glomeratus is better reflected by survival after shortterm salinity events, rather than growth inhibition due to long-term salinity imposed gradually.
To examine the importance of Na+ and Cl- to osmotic adjustment in a salt-tolerant ecotype of the C4 nonhalophyte Andropogon glomeratus, plants were watered with sorbitol, a neutral osmoticum, and synthetic seawater, for five days. Gas exchange measurements were made during the course of the watering treatment and during a recovery period following treatment. Leaf osmotic adjustment occurred only in plants watered with seawater, and was associated with an increase in Na+ and Cl- concentrations. Estimates of the molar concentrations indicated these ions could account for 95% of the leaf osmotic adjustment. Net photosynthetic CO2 uptake was less effected during the watering treatment, and photosynthetic recovery was greater following the treatment in plants watered with seawater. Photosynthetic inhibition was related primarily to metabolic factors, including a decrease in carboxylation efficiency. A model is presented for a mechanism promoting tolerance to transient seawater inundation in A. glomeratus.
Measurements of leaf spectral reflectance, the components of water potential, and leaf gas exchange as a function of leaf water content were made to evaluate the use of near-infrared reflectance as an indicator of plant water status. Significant correlations were determined between spectral reflectance at 810 nm, 1665 nm, and 2210 nm and leaf relative water content, total water potential, and turgor pressure. However, the slopes of these relationships were relatively shallow and, when evaluated over the range of leaf water contents in which physiological activity occurs (e.g., photosynthesis), had lower r2 values, and some relationships were not statistically significant. NIR reflectance varied primarily as a function of leaf water content, and not independently as a function of turgor pressure, which is a sensitive indicator of leaf water status. The limitations of this approach to measuring plant water stress are discussed.
Sunflower (Helianthus annuus L.) was raised according to common agricultural practices except that drought was imposed from the 20th day after planting in order to accentuate the natural daily cycling in leaf water potential (Ψleaf). The nature of the processes involved in regulating assimilation on a diurnal time scale was then investigated using techniques of gas exchange analysis. Although Ψleaf decreased from −0.5 to −1.1 MPa between predawn and mid-afternoon, autoradiographs of recent 14C-photoassimilation in leaves showed no evidence for inhomogeneities in stomatal apertures at any time off the day. Only by severing the tap root and allowing the shoot to dry rapidly could ‘patchiness’ be induced. A significant diurnal decline in assimilation (A) (from ∼ 31 to 25 μmolCO2 m−2 s−1) was accompanied by declining leaf conductance but, since there was no significant change in intercellular [CO2] (Ci), it is unlikely that A was being limited by the supply of CO2 for carboxylation. Instead, a decrease in the initial slope of A/Ci curves taken over the course of the day showing a decreased apparent affinity of the CO2 reductive processes for CO2, indicating chloroplast-level control. By briefly treating the leaf with intercellular CO2 levels near the CO2 compensation point, the relationship between A and Ci could be significantly shifted. These experiments revealed a strong biochemical element contributing to the lowre photosynthetic rates that develop over the course of a day in field-grown sunflower. In addition, it was seen that rapid adjustments could be made in the level of the biochemical control and that they were probably initiated by changes in the intercellular CO2 levels.
This paper discusses whole-plant responses to salinity in order to answer the question of what process limits growth of non-halophytes in saline soils. Leaf growth is more sensitive to salinity than root growth, so we focus on the process or processes that might limit leaf expansion. Effects of short-term exposure (days) are considered separately from long-term exposure (weeks to years). The answer in the short term is probably the water status of the root and we suggest that a message from the root is regulating leaf expansion. The answer to what limits growth in the long term may be the maximum salt concentration tolerated by the fully expanded leaves of the shoot; if the rate of leaf death approaches the rate of new leaf expansion, the photosynthetic area will eventually become too low to support continued growth.
The sensitivity of photosystem II to NaCl was compared in thylakoids isolated from the salt-tolerant mangrove, Avicennia marina, and the salt-sensitive pea, Pisum sativum. There were no indications of fundamental differences in photosystem II between these two species. Rates of oxygen evolution declined linearly with increase in NaCl from 10 to 500 mol m⁻³, with both species being equally sensitive. The NaCl-induced changes in Chl a fluorescence characteristics of intact thylakoids were substantially reversed by addition of hydroxylamine, indicating that the water-oxidizing site of photosystem II is sensitive to the NaCl concentration. These results are consistent with NaCl-induced depletion of the 23 and 17 kDa proteins from photosystem II-enriched membrane sheets. While the inhibition of oxygen-evolving activity by 500 mol m⁻³ NaCl was substantially reversed in thylakoids kept in the dark, 500 mol m⁻³ NaCl induced marked photoinhibitory damage in illuminated thylakoids. Thus, accumulation of ions in the chloroplasts of either salt-tolerant or salt-sensitive species would probably result in rapid damage to photosystem II, particularly in the light.
The pressure-bomb technique as developed by Scholander and colleagues is reviewed. A theoretical analysis of the equilibrium
water-relations of individual cells of a twig is derived taking due account of the fact that each cell has a unique solute
concentration, fluid volume, shape, and unique mechanical constraint by virtue of its cell-wall structure and attachment to
nearest neighbours. These equations combine to give a complete description of the whole twig in response to mechanical (air
pressure) stress. Our theoretical analysis suggests that the ‘pressure-volume curve’ can be related quantitatively to meaningful
bulk parameters of water relations: viz. the total osmolar content of the symplast Ns, the original volume of the symplast Vo, the volume expressed from the symplast Ve, the gas-pressure of the bomb P, and the volume-averaged turgor pressure (the sum of the products of the relative volume and turgor pressure of each cell).
An empirical relation for the volume-averaged turgor pressure of twigs is found which fits all species examined; it also fits
the turgor pressure relation for single (Nitella) cells.
Many plant processes are affected by mild water stress, with cell growth
probably the most sensitive. Except for turgor-mediated processes, the
physicochemical basis for the transduction of small changes in water
status into alterations in metabolism remains obscure. Turgor pressure
is assigned a critical role in cell growth: the physical force needed to
sustain enlargement. Simple physical models relating growth to turgor
are conceptually useful in examining effects of water stress but can be
misleading because metabolic and regulatory responses may be marked and
vary temporally. Osmotic adjustment has long been known as a means by
which higher plants adapt to salinity, with much of the cell osmotica
being ionic and accumulated from the medium. Though not generally
recognized, osmotic adjustment also appears to be an important mechanism
for adaptation to water-limiting conditions, even in mesophytic plants.
In this case much of the osmotica might possibly be internally
generated. Recent field data on seasonal and diurnal adjustment and
vertical water-potential gradients in plant canopies are discussed
relative to growth and water-potential components.
The comparative responses of photosynthesis and growth to salinity were investigated for two C3 and one C4 species native to the tidal marshes of the San Francisco Bay-Sacramento River estuary of Northern California. At low salinities (0 or 150 meq l-1), where photosynthetic rates were maximal for all species, the C4 grass Spartina foliosa maintained the highest photosynthetic capacity and the C3 stem-succulent shrub Salicornia virginica the lowest; photosynthetic rates of the C3 sedge Scirpus robustus were intermediate. Differences in photosynthetic responses to intercellular CO2 pressure and temperature were consistent with those generally observed between C3 and C4 plants.
CO2 uptake was reduced at salinities above 150 meq l-1 in Scirpus and 300 meq l-1 in Spartina. In contrast, Salicornia exhibited no inhibition of CO2 uptake even at 450 meq l-1 salinity. Analysis of the responses to intercellular CO2 partial pressures showed that the inhibition of photosynthesis by high salinity in both Spartina and Scirpus is primarily accounted for by reduced photosynthetic capacity of the mesophyll, and secondarily, by reduced leaf conductances.
Species differences in relative growth rate (RGR) almost exactly opposed the differences in photosynthetic rates; the highest RGR was found in Salicornia and the lowest in Spartina. This reversal is accounted for by the greater allocation to photosynthetic shoots in Salicornia, which more than compensated for the lower photosynthetic capacity per unit surface area. RGR was more sensitive to salinity than photosynthetic rate in all three species, but the same relative sensitivities held. For Scirpus, reduced leaf elongation rates and changes in allocation patterns account for the greater limitation by salinity of RGR than of photosynthesis, and may be a primary factor restricting productivity of this species in saline habitats.
Parker, W. C. and Pallardy, S. G. 1987. The influence of resaturation method and tissue type on pressure-volume analysis of Quercus alba L. seedlings.—J. exp. Bot. 38: 535–549.
The effect of resaturation method and amount of woody tissue on pressure-volume analysis was investigated using material collected from Quercus alba L. seedlings. Leaves excised from well-irrigated, intact plants had lower initial xylem pressure potentials than did leaves resaturated by two artificial methods. Differential capacity for tissue rehydration among the three methods was linked to shifts in the relative position of pressure-volume curves, and differences in the osmotic potential and relative water content at which turgor loss occurred were observed. Pressure-volume curves from leaves resaturated by all three methods contained ‘plateaus’ near full turgor, where xylem pressure potential declined only slightly with relative water content. These plateaus were apparently associated with apoplastic water that accumulated in intercellular spaces of the leaf near full turgidity, and acted to buffer changes in leaf xylem pressure potential as tissues dehydrated. The presence of this water has implications for derived water relations parameter estimates. Pressure-volume curves for excised shoots also exhibited plateaus, but the relationship between xylem pressure potential and relative water content over this region was steeper than was found for leaves. Shoot osmotic potentials were somewhat lower than those for leaves. The slope of the linear portion of shoot pressure-volume curves was more shallow than for single leaves, a response associated with comparatively lower values of the symplastic water fraction in shoots.
Measurements of gas exchange characteristics were made on intact, attached leaves of hydroponically grown seedlings of Avicennia marina (Forstk.) Vierh. var australasica (Walp.) Moldenke as the NaCl concentration of the culture solution was varied by step changes of 50 millimolar NaCl every 2nd day from 50 to 500 to 50 millimolar NaCl. The CO(2) assimilation rate, stomatal conductance, intercellular CO(2) concentration, and evaporation rate decreased at salinities above 250 millimolar NaCl and recovered substantially upon return to the original salinity.The assimilation rate was measured as a function of the intercellular CO(2) concentration [A(c(i)) curve]. The lower linear portion of this curve was insensitive to variation in salinity, whereas the upper nonlinear portion declined with increasing salinity, indicating a reduction in the capacity for CO(2) assimilation which recovered upon return to the original salinity. Stomatal conductance changed such that the intercellular CO(2) concentration measured under normal atmospheric conditions occurred in the transition between the lower, linear and upper nonlinear portions of the A(c(i)) curve. Thus, stomatal conductance and photosynthetic capacity together co-limited the assimilation rate. The changes in gas exchange characteristics were such that water loss was minimal relative to carbon gain.
Gas exchange characteristics were studied in two mangrove species, Aegiceras corniculatum (L.) Blanco and Avicennia marina (Forstk.) Vierh. var australasica (Walp.) Moldenke, grown under a variety of salinity and humidity conditions. The assimilation rate was measured as a function of the intercellular CO(2) concentration [A(c(i)) curve]. The photosynthetic capacity decreased with increase in salinity from 50 to 500 millimolar NaCl, as shown by decline in both the initial linear slope and the upper plateau of the A(c(i)) curve, with A. corniculatum being the more sensitive species. The decline in photosynthetic capacity was enhanced by increase in the leaf to air vapor pressure difference from 6 to 24 millibars, but this treatment caused a decrease in only the upper plateau of the A(c(i)) curve. Stomatal conductance was such that the intercellular CO(2) concentration obtaining under normal atmospheric conditions occurred near the transition between the lower linear and upper plateau portions of the A(c(i)) curves. Thus, stomatal conductance and photosynthetic capacity together co-limited the assimilation rate, which declined with increasing salinity and decreasing humidity. The marginal water cost of carbon assimilation was similar in most treatments, despite variation in the water loss/carbon gain ratio.
Gas exchange measurements were made on plants from two natural populations differing in salt tolerance of Andropogon glomeratus, a C(4) nonhalophyte, to examine the effect of salinity on components responsible for differences in photosynthetic capacity. Net CO(2) uptake and stomatal conductance decreased with increasing salinity in both populations, but to a greater extent in the inland (nontolerant) population. The intercellular CO(2) concentrations increased with increasing salinity in the inland population, but decreased in the marsh (tolerant) population. Water use efficiency decreased as salinity increased in the inland population, and remained unchanged in the marsh population. Carboxylation efficiency decreased and CO(2) compensation points increased with increasing salinity in both populations, but to a lesser extent in the marsh population. Carboxylation efficiencies were higher with 2% relative to 21% atmospheric O(2) in salt stressed plants, suggesting that a decrease in the carboxylation:oxygenation ratio of ribulose 1,5-bisphosphate carboxylase/oxygenase was partly responsible for the decrease in photosynthetic capacity. Populational differences in photosynthetic capacity were the result of greater salinity-induced changes in carboxylation efficiency in the inland population, and not due to differences in the stomatal limitation to CO(2) diffusion.
The water, ion, proline, amide, amino acid and quaternary onium contents of ecotypes of Agrostis stolonifera isolated from salt marsh, spray zone and inland habitats were determined over a range of external salt concentrations. When grown at high salinites the plants exhibited inhibition in the root water absorption and reduction in the shoot water content, these being most pronounced in the inland ecotype and least in the salt marsh ecotype. In the presence of salt the accumulation of Na⁺ and Cl⁻ in both shoots and roots was accompanied by a decline in tissue potassium content. At high salinities the increase in tissue ion content was greatest in the inland ecotype and least in the salt marsh ecotype. Proline, asparagine, glutamine, serine and glycine betaine showed increases in response to salinity, these being most pronounced in the salt marsh ecotype. The inland and spray zone ecotypes exhibited marked decreases in the aspartate and glutamate contents when grown at high salinities. With polyethylene glycol or mannitol in culture solutions, the salt marsh ecotype exhibited a greater ability to resist losses in shoot water content and to increase shoot proline, asparagine, glutamine and serine contents, than the inland and spray zone ecotypes. Changes in the solute and water status are discussed in relation to salt tolerance of the ecotypes.
Pressure-volume curves were measured in three co-occurring chaparral shrubs, Arctostaphylos glandulosa, Quercus dumosa, and Ceanothus greggii, during a seasonal drought cycle. The pressure-volume approach was used to quantify diurnal and seasonal changes in plant water relations. Field measurements of plant water potentials and microclimate were also made to relate the pressure-volume results to the field setting. The seasonal trend was toward increasingly negative osmotic potentials with little (Q. dumosa) or no (A. glandulosa and C. greggii) recovery following the end of the drought. Shifts in the turgor loss point occurred both seasonally and diurnally. The largest diurnal shifts occurred during periods of maximum air temperature and minimum soil water potential. Concurrent field measurements of water potential indicate that these shifts were necessary for preventing turgor loss during periods of midday water stress in Q. dumosa and C,. greggii. The shrubs differed in their mode of seasonal osmotic adjustment. Ceanothus greggii accomplished changes in osmotic potential by variation in the osmotic water volume; the other two shrubs appeared to accomplish such changes largely by solute variation while maintaining relatively constant osmotic water volumes.
Spartina patens is a coastal grass species which exhibits a wide ecological amplitude. At the center of its latitudinal distribution, it successfully colonizes a diversity of contrasting maritime habitats which impose divergent selection regimes. To investigate the genetic base of this ecological amplitude, three subpopulations were examined along a 200 m transect across one of the barrier islands of North Carolina. Common environment studies of sampled clones revealed significant divergence among closely adjacent dune, swale, and salt marsh subpopulations for a variety of morphometric and physiological traits. These differences can be interpreted in adaptive terms. Low levels of gene flow among subpopulations, inbreeding (intraclonal and matings among related clones), and intense disruptive selection pressure are most likely to promote the observed microdifferentiation. The dune subpopulation was comprised of genotypes that channel a great proportion of resources into vegetative and sexual reproduction than do genotypes of other subpopulations. These traits may be advantageous in the unstable, colonizing environment of the dune. In addition, individuals found here showed greater salt and drought tolerance, and elicited better responses to low soil nutrient conditions. In the marsh, by contrast, individuals tended to be larger but with a lower reproductive output. These characters may be advantageous in a more stable environment where intraspecific competition is high and seedling establishment is rare. Marsh genotypes were also less tolerant of drought and salinity, but responded better to high soil nutrients than dune plants. Many but not all characteristics of swale genotypes tended to be intermediate between those of the dune and marsh (cf. Silander, 1979). The success of Spartina patens across a broad range of coastal habitats can be attributed to a flexible breeding system, which enhances genetic variation while ensuring reproductive success, and a colonizing ability which allows rapid preemption of space following perturbation.
A series of experiments is presented investigating short term and long term changes of the nature of the response of rate of CO2 assimilation to intercellular p(CO2). The relationships between CO2 assimilation rate and biochemical components of leaf photosynthesis, such as ribulose-bisphosphate (RuP2) carboxylase-oxygenase activity and electron transport capacity are examined and related to current theory of CO2 assimilation in leaves of C3 species. It was found that the response of the rate of CO2 assimilation to irradiance, partial pressure of O2, p(O2), and temperature was different at low and high intercellular p(CO2), suggesting that CO2 assimilation rate is governed by different processes at low and high intercellular p(CO2). In longer term changes in CO2 assimilation rate, induced by different growth conditions, the initial slope of the response of CO2 assimilation rate to intercellular p(CO2) could be correlated to in vitro measurements of RuP2 carboxylase activity. Also, CO2 assimilation rate at high p(CO2) could be correlated to in vitro measurements of electron transport rate. These results are consistent with the hypothesis that CO2 assimilation rate is limited by the RuP2 saturated rate of the RuP2 carboxylase-oxygenase at low intercellular p(CO2) and by the rate allowed by RuP2 regeneration capacity at high intercellular p(CO2).
Phaseolus vulgaris (cv. Hawkesbury Wonder) was grown over a range of NaCl concentrations (0–150 mM), and the effects on growth, ion relations and photosynthetic performance were examined. Dry and fresh weight decreased with increasing external NaCl concentration while the root/shoot ratio increased. The Cl- concentration of leaf tissue increased linearly with increasing external NaCl concentration, as did K+ concentration, although to a lesser degree. Increases in leaf Na+ concentration occurred only at the higher external NaCl concentrations (≧100 mM). Increases in leaf Cl- were primarily balanced by increases in K+ and Na+. X-ray microanalysis of leaf cells from salinized plants showed that Cl- concentration was high in both the cell vacuole and chloroplast-cytoplasm (250–300 mM in both compartments for the most stressed plants), indicating a lack of effective intracellular ion compartmentation in this species. Salinity had little effect on the total nitrogen and ribulose-1,5-bisphosphate (RuBP) carboxylase (EC 4.1.1.39) content per unit leaf area. Chlorophyll per unit leaf area was reduced considerably by salt stress, however. Stomatal conductance declined substantially with salt stress such that the intercellular CO2 concentration (C
i) was reduced by up to 30%. Salinization of plants was found to alter the δ13C value of leaves of Phaseolus by up to 5‰ and this change agreed quantitatively with that predicted by the theory relating carbon-isotope fractionation to the corresponding measured intercellular CO2 concentration. Salt stress also brought about a reduction in photosynthetic CO2 fixation independent of altered diffusional limitations. The initial slope of the photosynthesis versus C
i response declined with salinity stress, indicating that the apparent in-vivo activity of RuBP carboxylase was decreased by up to 40% at high leaf Cl- concentrations. The quantum yield for net CO2 uptake was also reduced by salt stress.
The water, ion, proline, amide, amino acid and quaternary onium contents of ecotypes of Agrostis stolonifera isolated from salt marsh, spray zone and inland habitats were determined over a range of external salt concentrations. When grown at high salinites the plants exhibited inhibition in the root water absorption and reduction in the shoot water content, these being most pronounced in the inland ecotype and least in the salt marsh ecotype. In the presence of salt the accumulation of Na+ and Cl− in both shoots and roots was accompanied by a decline in tissue potassium content. At high salinities the increase in tissue ion content was greatest in the inland ecotype and least in the salt marsh ecotype. Proline, asparagine, glutamine, serine and glycine betaine showed increases in response to salinity, these being most pronounced in the salt marsh ecotype. The inland and spray zone ecotypes exhibited marked decreases in the aspartate and glutamate contents when grown at high salinities.
With polyethylene glycol or mannitol in culture solutions, the salt marsh ecotype exhibited a greater ability to resist losses in shoot water content and to increase shoot proline, asparagine, glutamine and serine contents, than the inland and spray zone ecotypes.
Changes in the solute and water status are discussed in relation to salt tolerance of the ecotypes.
Using the pressure bomb technique, measurements have been made of the tissue water relations of seedlings of three populations of Eucalyptus viminalis, and of adult shoots of trees from two contrasting sites, to facilitate an understanding of the physiological basis of intra-specific variation in drought resistance.
For both juvenile and adult material, the shoot water potential of the most drought resistant population declined most rapidly with decreasing water content. Estimates of the fraction of water in the cell walls at full turgor were also greatest for this population, averaging 0.36 for juvenile and 0.40 for adult material. Calculated values for the bulk modulus of elasticity of the walls were very variable, but tended to be higher, in adult than juvenile tissues.
The results suggest that in dry habitats there has been selection for plants which, during temporary periods of drying, can maintain a water content above the critical level for cell damage. Differences between two very closely situated field populations emphasize the need to consider the role of edaphic as well as climatic factors in selection for drought resistance.
Eight populations ofAgrostis stolonifera, collected from maritime and inland habitats, were grown in solution culture and in sand culture at various concentrations of sodium chloride from 0 ppm to 5,000 ppm Na.
NaCl had less effect upon the dry weight yield of populations from maritime habitats, with soils of high Na content, than upon populations from inland or maritime habitats with soils of low Na content. The correlation between per cent reduction in dry weight yield and the Na content of the native soil of each population was r=−0.73. Populations from inland or maritime habitats, with soils of low Na content, contained more Na in their shoot materials, and higher Na/K ratios, than did populations from high Na soils, at all Na concentrations.
The effect of NaCl upon the root elongation of each population was not correlated with the effect upon dry weight yield, nor with the Na content of their native soil. The effect of Na Cl upon root elongation was highly dependent upon the composition of the culture solution used. It is concluded that the effect of NaCl on root elongation is not an adequate measure of salinity tolerance in this species.
This research was undertaken to investigate differences in salt tolerance under conditions in which salinity is increased gradually and maintained for long periods or increased rapidly and maintained for shorter periods. The responses of populations of a C4 nonhalophytic grass, Andropogon glomeratus, to long- and short-term salinity were measured under controlled environment conditions. Additionally, plants from a salt marsh population and an inland population were transplanted into a salt marsh and their survival compared. The relative growth reductions in the salt marsh and the inland populations under long-term salinity were similar. Survival of seedlings of 4 populations inundated with full-strength seawater over a relatively short period indicated differential capacities to tolerate soil salinities imposed in a manner similar to tidal inundation in a salt marsh. The greater survival of plants from the marsh population transplanted into the salt marsh further indicated genetic differentiation between the populations. These results indicate that genetic differentiation to salt tolerance in A. glomeratus is better reflected by survival after shortterm salinity events, rather than growth inhibition due to long-term salinity imposed gradually.
ALTHOUGH the tolerance of plants to salt is of great economic importance and has received detailed attention, data for contrasting populations of species that occur naturally in saline and non-saline habitats are limited. Demonstrations of the significance of salt in the distribution of forms of Typha by McMillan1 and McNaughton2 are notable exceptions. We have therefore examined the salt tolerance of populations of Festuca rubra L., which occurs in both the lower and upper regions of salt marshes and in the adjacent non-saline uplands, and of Agrostis stolonifera L. which coexists with Festuca in the upper marsh and upland. Five such populations were collected from each of two geographically separate but otherwise similar sites (Aber, Caernarvonshire and Malltraeth, Anglesey).
The limitations on carbon dioxide assimilation by plants caused by stomata, particularly when the plant is under stress, are discussed. Mechanisms by which stomatal movement is integrated with photosynthesic requirements are described.
Abstract Individual leaves and stems were analysed for Na+, Cl−, K+ and water content in two clones of Agrostis stolonifera differing in salt resistance, during 14 d of treatment with NaCl, 100 and 200 mol m−3, and a further 7 d in a salt-free medium. Great differences in ion and water content were revealed between individual organs, and organ-by-organ analysis also emphasized the differences between the clones better than whole shoot analysis. In both clones, Na+ and Cl− accumulated to the greatest degree in the older leaves, but for corresponding organs, the concentrations were lower in the more tolerant clone. In the sensitive clone, the lowest leaves dehydrated in 200 mol m−3 NaCl and failed to recover, while the plants of the more resistant clone maintained viable water content in all organs. In the resistant clone, K+ concentration decreased less in response to salt treatment than in the more sensitive clone. For a full appreciation of the plants' reactions, it was found necessary to express the analytical data on several bases, namely, per unit dry-weight, unit water, and total ion-content.
The tolerance to sodium chloride of clones of Agrostis stolonifera from salt marsh, spray zone, and inland habitats was measured in water cultures by a rooting technique and by growth analysis. The order of tolerance was found to be: salt marsh > spray zone > inland. The two methods of measurement of tolerance were found to show good agreement. Salt marsh plants were found to be more resistant to low dissolved oxygen concentrations in the culture solution than plants from the spray zone and inland habitats. With polyethylene glycol 6000 in culture solution, the pattern of resistance to osmotic stress in the absence of sodium chloride was similar to the pattern of resistance to salt.
1) This review concentrates on the effect of sodium chloride on the growth of higher plants, being primarily concerned with relatively high concentrations i.e. 50 mmol 1 ‐1 and above, though something is also said about those instances when sodium acts as a micronutrient. Emphasis is placed on particular species or genera for which enough information is available to discuss possible mechanisms.
(2) Trace amounts of sodium are required for the growth of plants using the C 4 pathway of carbon fixation and may also be important in plants with Crassulacean acid metabolism.
(3) The increased growth of Beta vulgaris brought about by sodium chloride can in part be explained by a sparing effect on potassium. However, growth is still increased when sufficient potassium is available. Complementary studies with rubidium indicate that the hormone balance in the plant may be changed. Sodium chloride also increases the level of sucrose in storage roots and allows beet plants to withstand water stress more readily, possibly by increased turgor pressure.
(4) Sodium chloride increases production of dry matter in C 4 species of Atriplex under conditions of low relative humidity because water loss is reduced and photo‐synthesis hardly affected.
(5) Succulence in many plants is stimulated by salinity. The essential basis of the phenomenon is an increased water potential gradient between the leaf and the external medium. In some instances, it is the accumulation of chloride which is important; in others it is the accumulation of cations, when potassium can be as effective as sodium.
(6) Salinity reduces the final area achieved by growing leaves. Most of the studies have been made on Phaseolus vulgaris and an important early event is the reduction in the rate of expansion of the epidermal cells and this may be accompanied by a decrease in their number. Reduction of epidermal cell size is a result of water stress; sodium chloride may directly affect cell division, though water stress cannot be ruled out. Whether salinity brings about inhibition of cell division depends upon the calcium content of the medium – a high content is accompanied solely by a reduction in epidermal cell size.
(7) Hormones, as yet unspecified, may play an important part in response of a growing leaf to salinity. However, there is no evidence that sodium chloride per se has an effect on hormone balance within the plant. So far, any measured changes in levels of specific hormones can be ascribed to the osmotic effects of the saline medium.
(8) Two estimates by flux analysis of cytoplasmic concentration of sodium in plants growing in conditions of high salinity give a value of around 150 mmol 1 ‐1 . There is no similar information for chloride. Other techniques (histochemistry and X‐ray micro‐probe analysis) give questionable information.
(9) There is now extensive information to show that enzymes of halophytes (other than ATPases) do not differ significantly from those of other higher plants with respect to their sensitivity in vitro to sodium chloride. There is a need for further work with respect to the activity of enzymes in the presence of those metabolites which have the highest cytoplasmic concentration.
(10) Sodium‐stimulated ATPases have been isolated from plant cells but their distribution amongst higher plants is restricted.
(11) There are a number of reports of changed metabolism brought about by saline treatments but it is not clear how far the effects of sodium chloride and water stress are confounded.
(12) Sodium appears to increase the sucrose levels in sugar beet by an inhibitory effect on product starch‐granule‐bound ADP‐glucose starch synthase.
(13) Reversal of a sodium pump located at the plasmalemma might have an effect on cell turgor.
(14) Sodium (like other monovalent cations) causes loss of materials from plant cells, possibly through an effect on carrier proteins; calcium prevents this from happening. Calcium also allows plants to grow better in saline conditions by a depression of sodium uptake by and transport within the plant. The properties and composition of the membranes of mesophytes and halophytes need to be compared.
(15) A saline medium exerts a major effect on plant growth through water stress to which a halophyte must adapt. As well as this, the cytoplasmic concentration of sodium chloride must be kept lower than the total cellular concentration of the salt. Unless this happens, it is likely that enzymic activity will be reduced due, in some instances, to an unspecific effect of a high concentration of monovalent cations and/or chloride and in other instances to competition between sodium and other cations, specifically potassium, for activation sites on enzymes, e.g. pyruvate kinase.
(16) Further work is required to separate the osmotic effects from the specific effect of sodium chloride after it has entered the plant. As well as this, it has become clear that more information is needed about the mineral nutrition of halophytes.
The dependence of leaf water potential (), osmotic potential () and turgor pressure (P) on relative water content (RWC) was determined for leaves of tall and short growth forms of Spartina alterniflora Loisel. from a site on Canary Creek marsh in Lewes, Delaware. Tall plants (ca. 1.5 m) occured along a drainage ditch where interstitial water salinity was approximately 20, and short plants (ca. 0.2 m) were 13 m away near a pan and exposed to 80 salinity during the most stressful period. Leaves were collected at dawn and pressure-volume measurements were made as they desiccated in the laboratory. Pressure equilibrium was used to measure , RWC was determined from weight loss and dry weight, was determined from the pressure volume curve, and P was calculated as the difference between and . Physical properties of the bulk leaf tissue that have a role in regulating water balance of the two growth forms were estimated: relative water content of apoplastic water (RWCa) relative water content at zero turgor (RWC0), the bulk modulus of elasticity (E), and water capacity (C
w). There were no detectable temporal trends in any of the parameters measured from Nune through September and no significant differences between the two growth forms when compared on the basis of RWCa, RWC0, E, and C
w. There was a clear difference between the two growth forms with respect to ; at RWC0, was-4.50.40 MPa for short form plants and-3.30.40 MPa for tall form.Turgor pressure of plants in the field (P) was lower in leaves from short form than for the tall form plants with average difference of about 0.4 MPa. In July, P in short form leaves dropped to zero by mid-morning as expected for leaves experiencing water stress.These results show that S. alterniflora is capable of reducing osmotic potential in response to increased salinity and that turgor pressure was lower in short growth form than in tall forms.
Seed and transplanted adult plants from populations of Festuca rubra, collected from inland, salt-marsh and sand-dune sites were grown on culture solution with added sodium chloride. The growth of the populations of the three habitats was reduced differentially by salt. The salt marsh ecotype Festuca rubra ssp. litoralis was only slightly affected and the inland ecotype F. rubra ssp. rubra was severely retarded at 60 mM NaCl. The dune ecotype F. rubra ssp. arenaria had an intermediate tolerance. The tolerant ecotypes accumulated less sodium chloride as compared to the sensitive ecotype, suggesting that salt tolerance is caused in part by salt exclusion.
In addition, the dune ecotype F.r. arenaria appeared to be more drought tolerant than the salt marsh ecotype. Abscission of salt-saturated leaves does not function as an adaptation to salinity in Festuca rubra.
All three ecotypes accumulated proline with increased salinity. The response was most pronounced in the drought tolerant F.r. arenaria, indicating that proline accumulation is a response to osmotic stress rather than to ion-specific effects of salinity. The observed differences in salt tolerance may be explained by differential sensitivity to toxic effects of sodium chloride.
The occurrence on a beach plain of closely adjacent populations of F.r. arenaria and F.r. litoralis, differing markedly in salt tolerance, is briefly discussed.
Laboratory gas exchange measurements were conducted on four pioneering beach species from southern California. Atriplex leucophylla (Moq.) D. Dietr., a C4 species, had a photosynthetic temperature optimum substantially higher than leaf temperatures normally experienced on the beach during the primary growing season. The C3 species, Cakile maritima Scop., Ambrosia chamissonis Less. and Abronia maritima Nutt. ex Wats., had photosynthetic temperature optima close to their growth temperature and higher photosynthetic rates than the C4 species at normal field growth temperatures. Atriplex leucophylla had higher mesophyll conductances which resulted in higher water use efficiencies at all measurement temperatures. Leaf chlorophyll and protein contents were not correlated with photosynthetic rates. The possible significance of water use efficiency is discussed in relation to the characteristics of the beach habitat.
The characteristics of the photosynthetic apparatus of 11 Hawaiian Euphorbia species, all of which possess C4 photosynthesis but range from arid habitat, drought-deciduous shrubs to mesic or wet forest evergreen trees and shrubs, were investigated under uniform greenhouse conditions. Nine species exhibited CO2 response curves typical of C4 plants, but differed markedly in photosynthetic capacity. Light-saturated CO2 uptake rates ranged from 48 to 52 μmol m-2 s-1 in arid habitat species to 18 to 20 μmol m-2 s-1 in mesic and wet forest species. Two possessed unusual CO2 response curves in which photosynthesis was not saturated above intercellular CO2 pressures [p(CO2)] of 10 to 15 Pa, as typically occurs in C4 plants.
Both leaf (g′1) and mesophyll (g′m) conductances to CO2 varied widely between species. At an atmospheric p(CO2) of 32 Pa, g′1 regulated intercellular p(CO2) at 12–15 Pa in most species, which supported nearly maximum CO2 uptake rates, but did not result in excessive transpiration. Intercellular p(CO2) was higher in the two species with unusual CO2 response curves. This was especially apparent in E. remyi, which is native to a bog habitat. The regulation of g′1 and intercellular p(CO2) yielded high photosynthetic water use efficiencies (P/E) in the species with typical CO2 response curves, whereas P/E was much lower in E. remyi.
Photosynthetic capacity was closely related to leaf nitrogen content, whereas correlations with leaf morphological characteristics and leaf cell surface area were not significant. Thus, differences in photosynthetic capacity may be determined primarily by investment in the biochemical components of the photosynthetic apparatus rather than by differences in diffusion limitations. The lower photosynthetic capacities in the wet habitat species may reflect the lower light availability. However, other factors, such as reduced nutrient availability, may also be important.
Enzymes which are affected by the addition of inorganic salts during in vitro assay were extracted from salt-sensitive Phaseolus vulgaris, salt-tolerant Atriplex spongiosa, and Salicornia australis and tested for sensitivity to NaCl. In each case malate dehydrogenase, aspartate transaminase, glucose 6-phosphate dehydrogenase, and isocitrate dehydrogenase showed NaCl responses similar to those found for commercially available crystalline enzymes from other organisms. Enzymes extracted from plants grown in saline cultures showed no important changes in specific activity or salt sensitivity. Interaction of pH optima and NaCl concentrations suggests that enzymes may differ in the way they respond to salt treatment.
The objective of this research was to measure the short term osmotic adjustment of Salicornia europaea L. ssp. rubra (A. Nels) Breitung when suddenly exposed to 100 millimolar NaCl. Plants were grown hydroponically, shocked with 100 millimolar NaCl added to the culture solution, and stem tips analyzed for free inorganic ions and small organic molecules at intervals up to 72 hours. In the first 2 hours, the calculated leaf osmoticum showed a net increase of 158.8 millimolar most of which was free Mg(2+) (+135.3 millimolar). Total sugars increased almost 5-fold by the 6th hour, enough to provide sufficient osmoticum for the cytoplasm if only partially confined there. By 24 hours, all measured osmotica had decreased except Na(+), Mg(2+), Cl(-), and proline, with the net increase being 208 millimolar. By 72 hours, there was a net gain of 356 millimolar in osmotica of the stem tips, due to Na(+) (+233.3 millimolar), Cl(-) (+306.7 millimolar), and a small increase in sugar and proline (+3.5 millimolar), with all other osmotica decreasing in concentration. Compatible osmotica did not change sufficiently to account for osmotic balance between vacuole and cytoplasm; consequently, there must have been a reapportionment of osmotica within the cell in the short time duration of this experiment.
Effects of salinity on growth and
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Effect of salinity on leaf gas exchange in two populations of a C4 nonhalophyte Seasonal and diurnal water rela-tions adjustments in three evergreen chaparral shrubs
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Effects of stabilizing solutes on salt activation of phosphoenolpyruvate carboxylase from var-ious plant sources The genetic basis of the ecological amplitude of Spartina patens I. Morphometric and physiologi-cal traits
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Shomer-Ilan A, Waisel Y (1986) Effects of stabilizing solutes on salt activation of phosphoenolpyruvate carboxylase from var-ious plant sources. Physiol Plant 67:408~414 Silander JA, Antonovics J (1979) The genetic basis of the ecological amplitude of Spartina patens I. Morphometric and physiologi-cal traits. Evolution 33 : 1114-1127