Contrasting adaptation and optimization of stomatal traits across communities at continental-scale

The maximum stomatal conductance (g), a major anatomical constraint on plant productivity, is a function of the stomatal area fraction (f) and stomatal space-use efficiency (e). However, f and g have been considered as equivalents, with e rarely considered, and their adaptation to the environment and their regulation of ecosystem productivity are unclear. Here, we analyzed the community-weighted mean, variance, skewness, and kurtosis of stomatal traits from tropical to cold-temperature forests. The variance of g and f was higher for arid sites, indicating greater functional niche differentiation, whereas that for e was lower, indicating convergence in efficiency. Besides, when other stomatal trait distributions remained unchanged, increasing kurtosis but decreasing skewness of g would improve ecosystem productivity, and f showed the opposite patterns. These findings highlight how the relative importance and equivalence of inter-related traits can differ at community scale.

Explaining the Atlas Cedar (Cedrus atlantica M.) dieback by studying Water relations of young plants subject to an edaphic drought

Cedrus atlantica M. stands from the Middle Atlas Mountains in Morocco have been severely affected by dieback. The edaphic water deficit could be the cause that triggered this phenomenon leading to the mortality of dying trees. The objective of this work is to analyze the ecophysiological behavior of Atlas cedar seedlings subjected to an edaphic drought of progressive intensity. During the drying cycle, the relative moisture content of the substrate decreased significantly to reach 12.71% at the end of the test; 4.27% and 2.88% respectively for the basaltic, calcareous, and sandy substrate. The pre-dawn water potential reached very low values of -32.25, -37.38, and -39.50 bar at the end of the water drying cycle. The critical water potential varied between -36 and -39 bar depending on the type of substrate. The mean maximum stomatal conductance under favorable water conditions was of the order of 330 mmol/m2/s. It was reduced, due to drying, in proportion to the reduction in substrate moisture content. Atlas cedar maintains gas exchange under conditions of severe water stress but can be lethal with extreme and recurrent droughts. This behavior can explain the development of the phenomenon of cedar stand decline, which is more accentuated especially with adverse ecological conditions.

Temperature and evaporative demand drive variation in stomatal and hydraulic traits across grape cultivars

Selection for crop cultivars has largely focused on reproductive traits, while the impacts of global change on crop productivity are expected to depend strongly on the vegetative physiology traits that drive plant resource use and stress tolerance. We evaluated relationships between physiology traits and growing season climate across winegrape cultivars to characterize trait variation across European growing regions. We compiled values from the literature for seven water use and drought tolerance traits and growing season climate. Cultivars with a lower maximum stomatal conductance were associated with regions with a higher mean temperature and mean and maximum vapor pressure deficit (VPD) (r 2 = 0.39 – 0.65, P < 0.05, N = 14 – 29). Cultivars with greater stem embolism resistance and more anisohydric stomatal behavior (i.e., a more negative water potential threshold for 50% stomatal closure) were associated with cooler regions (r 2 = 0.48 – 0.72, P < 0.03, N = 10 – 29). Overall, cultivars grown in warmer, drier regions exhibited traits that would reduce transpiration and conserve soil water longer into the growing season, but potentially increase stomatal and temperature limitations on photosynthesis under future, hotter conditions.

A continuum of stomatal responses to water deficits among 17 wine grape cultivars (Vitis vinifera)

Vitis vinifera L. cultivars have been previously classified as isohydric, near-isohydric, anisohydric or isohydrodynamic, depending on the study. To test the hypothesis that V. vinifera cultivars’ stomatal behaviour can be separated into distinct classes, 17 cultivars grown in a replicated field trial were subjected to three irrigation treatments to manipulate vine water status across multiple years. Predawn (ΨPD) and midday (Ψl) leaf water potential and midday stomatal conductance (gs) were measured regularly throughout several seasons. The relationship of gs to Ψl was best modelled as a sigmoidal function and maximum stomatal conductance (gmax), water status at the onset of stomatal closure (Ψl95), sensitivity of closure (gsensitivity) and water status at the end of closure (Ψl25) were compared. There were no significant differences in gmax among cultivars. Cultivar-specific responses of gs to Ψl were broadly distributed along a continuum based on the relationship between Ψl95 and gsensitivity. Season-long cultivar mean Ψl values were positively related to Ψl25. In general, cultivars responded similarly to one another at high and low water status, but their stomatal behaviour differed at moderate water deficits. The results show that V. vinifera cultivars possess both iso- and anisohydric stomatal behaviours that depend on the intensity of water deficits, and call into question previous classifications assuming a single behaviour.

Stomatal anatomy coordinates leaf size with Rubisco kinetics in the Balearic Limonium

Trait integration arises through both selection on functional coordination and shared developmental pathways. Different anatomical components must both work well and develop together to generate individuals with the appropriate physiology to survive and reproduce in their environment. In this study, we used a common garden experiment and Bayesian multilevel models to test whether stomatal anatomy coordinates leaf gas exchange, Rubisco kinetics, and leaf size across 10 closely related species of Limonium from the Balearic Islands. The results indicate that the anatomical determinants of maximum stomatal conductance, stomatal density and size, were functionally coordinated with Rubisco kinetics – species whose stomatal anatomy was correlated with low stomatal conductance have evolved Rubisco enzymes better adapted to low operational chloroplastic CO2 concentrations. Lower stomatal density was associated with greater leaf size, which can be explained by a greater proportion of pavement cells in large-leaved species. These results suggest that both selection for functional coordination (stomata and Rubisco kinetics) and shared development pathways (stomatal density and leaf area) likely shape patterns of trait integration between species.

Extreme salinity as a challenge to grow potatoes under Mars-like soil conditions: targeting promising genotypes

One of the future challenges to produce food in a Mars environment will be the optimization of resources through the potential use of the Martian substratum for growing crops as a part of bioregenerative food systems. In vitro plantlets from 65 potato genotypes were rooted in peat-pellets substratum and transplanted in pots filled with Mars-like soil from La Joya desert in Southern Peru. The Mars-like soil was characterized by extreme salinity (an electric conductivity of 19.3 and 52.6 dS m−1 under 1 : 1 and saturation extract of the soil solution, respectively) and plants grown in it were under sub-optimum physiological status indicated by average maximum stomatal conductance <50 mmol H2O m−2 s−1 even after irrigation. 40% of the genotypes survived and yielded (0.3–5.2 g tuber plant−1) where CIP.397099.4, CIP.396311.1 and CIP.390478.9 were targeted as promising materials with 9.3, 8.9 and 5.8% of fresh tuber yield in relation to the control conditions. A combination of appropriate genotypes and soil management will be crucial to withstand extreme salinity, a problem also important in agriculture on Earth that requires more detailed follow-up studies.