PS 15-188 - Variability of traits conferring drought resistance along a precipitation gradient in the perennial grass Schizachyrium scoparium

Abstract: Understanding the variability in functional traits related to climate within a species will facilitate predicting species responses to changes in climate. We quantified the variability of traits that confer drought resistance in the perennial grass species Schizachyrium scoparium across the steep precipitation gradient from east to west Texas. We sampled leaves from populations of Schizachyrium scoparium from five sites along the precipitation gradient in spring and again in late summer. We measured the stomatal density, guard cell lengths, minimum leaf conductance, leaf mass per area, and several additional functional traits. For leaves sampled during the spring, stomatal density decreased and stomatal lengths exhibited no pattern with increasing mean annual precipitation, while minimum leaf conductance and leaf mass per area trended higher with increasing precipitation. For leaves sampled during the late summer, leaf functional traits were not related to mean annual precipitation. Overall, the absolute variation in the functional traits for Schizachyrium scoparium along the precipitation gradient was only moderately greater than the variation in these traits for leaves sampled at different heights along individual tillers at the site with the highest precipitation. The low variability in the measured traits across the precipitation gradient may be due to Schizachyrium scoparium growing preferentially during periods of high water availability following rainfall, thereby minimizing advantages conferred by drought resistance traits.