Stomatal traits relate to habitat preferences of herbaceous species in a temperate climate

Abstract

Stomata enable plants to balance uptake of CO2 with water loss via transpiration. Previous studies have shown that stomatal size and density trade-off with one another and are related to a suite of environmental factors (light, atmospheric CO2 concentrations, moisture and temperature) which influence gas exchange. We examined the hypothesis that the habitat preferences of species are reflected in stomatal traits. Thus, we examined the relation of stomatal size and density of 36 herbaceous species along elevational gradients in relation to Ellenberg indicator values for light and moisture. The light value is a proxy for the transpiration demand due to exposure to radiation and air mass exchange, the moisture value reflects water supply. Additionally we measured carbon isotope discrimination (Δ13C), a proxy for intrinsic water use efficiency and internal CO2 concentration. Stomatal size changed in parallel on both sides of a leaf, whereas changes in density differed between sides depending on species identity. There was an increase in absolute variation of sizes and densities with increasing mean size and density respectively, but not in relative variation. Species with few but large stomata tended to adjust stomatal size across environmental gradients, whereas species with small but many stomata mainly adjusted stomatal density. A higher Ellenberg indicator value for light and a lower value for moisture was associated with equal distribution of stomata between leaf sides. The carbon isotope discrimination data indicated that amphistomatic species, which illustrated a preference for high radiation and high air mass exchange as well as for dry habitats, had higher water use efficiency. We conclude that stomatal traits such as size, density or the distribution between the two sides of the leaf are indicators of how species optimize carbon uptake and balance water loss and radiation gain.