Epidermal conductance as a component of dehydration avoidance in Digitaria californica and Eragrostis lehmanniana, two perennial desert grasses

Epidermal conductance (gmin) is water lost through the cuticle and stomata of plants when stomatal conductance is minimal. Low gmin may affect survival of perennial grasses by maintaining tissue hydration during drought. If true, populations from environments where drought is severe may exhibit reduced gmin compared to those from less arid environments. Success of invasive grasses may also be associated with reduced gmin compared to non-invasive competitors. Using plants grown in a single environment, we measured gmin of leaves from populations of Digitaria californica from environments with similar annual precipitation but differing in average drought severity (southern Arizona and western Texas, USA), and a population of the exotic species Eragrostis lehmanniana that has invaded sites occupied by D. californica in Arizona. Epidermal conductance was lower in the D. californica population from the more arid environment (Texas). Likewise, gmin was lower in E. lehmanniana than in the Arizona D. californica population. Shoot biomass production as a fraction of gmin was higher in E. lehmanniana than in the D. californica populations and was higher in the Texas D. californica population than in the Arizona population. This suggests that low gmin may be a component of drought avoidance in these grasses.