Plant responses to water stress are a strong influence on ecological adaptation and community assembly, especially as droughts become more severe with climate change. Species are known to differ strongly in their stomatal responses to leaf dehydration, and many studies have quantified the relationship of gs to Ψleaf, which mechanistic models and meta-analyses suggest is an important trait for plant and ecosystem drought tolerance. However, little is known of the relationship of gs responses to leaf dehydration to leaf structure, anatomy, and physiology, including turgor loss point (TLP), the leaf water potential that induces wilting, and leaf mass per area (LMA). Our study focuses on 15 morphologically and ecologically diverse California native tree and shrub species grown in a greenhouse common garden. We determined the response of stomatal conductance (gs; mmol m-2 s-1) to leaf water potential (Ψleaf) for leaves acclimated to high irradiance (>1000 µmol m-2 s-1) using a Delta-T AP4 porometer. We tested hypotheses for the relationship of stomatal closure to other leaf functional traits and to ecological specialization.
Results/Conclusions
Across species, stomatal closure was linked with ecological specialization, with evergreen chapparal species better able to maintain open stomata during leaf dehydration than deciduous or riparian species. Across species, 50% stomatal closure took place at a wide range of water potentials (Ψ_gs50 = -0.4 to -2 MPa), as did 95% stomatal closure (Ψ_gs95 = -0.6 to -3 MPa). Leaf dehydration at stomatal closure was weakly related to turgor loss point (TLP) but species varied strongly in the sequence of these traits, with stomatal closure occurring before TLP, approximately at TLP or after TLP depending on species. Stomatal closure responses were independent of LMA. This work highlights important species variation in stomatal closure responses, mechanistically independent of other drought-related functional traits. While stomatal closure can potentially be predicted to some degree from other functional traits, the variation in stomatal closure that is unexplained by other traits would play an important role in determining leaf and whole plant drought responses.