Intraspecific variation in stomatal architecture, gas exchange, and drought response of a dominant prairie grass sourced from broad climatic gradients

<p>Premise: Understanding how plant populations adapt to water limitation through stomatal traits is key to predicting drought responses. The dominant C~4 ~grass <em>Andropogon gerardi</em>, distributed across sharp climate gradients in North America, offers an excellent focal species to study stomatal architecture (size and density). Using a common garden, we tested how stomatal architecture relates to home climate, how stomatal architecture influences gas exchange, and how experimental drought affects these responses in a greenhouse. We hypothesized that aridity drives stomatal architecture, and experimental drought reduces stomatal size but increases density to maintain photosynthesis.</p> <p>Methods: In our first experiment, we measured stomatal architecture and gas exchange in 25 populations sourced across temperature (4–21°C) and precipitation (350–1400 mm yr⁻¹) gradients under well-watered conditions. A second experiment focused on eight populations (472–1356 mm yr⁻¹), subjected to drought (~15% soil moisture) or well-watered (30% control) to assess plasticity. Stomatal traits were measured with epidermal peels and light microscopy, gas exchange with a LI-COR 6400, and network analyses were used to characterize adaptive strategies. </p> <p>Results: Arid populations exhibited smaller, denser stomata compared to wet populations and networks demonstrated a trade-off between stomatal size and density. Under experimental drought, stomatal size decreased while density increased, with dry populations showing fewer changes than wet populations. Key traits in the network were stomatal size and water-use efficiency.</p> <p>Conclusions: This study reveals that <em>A. gerardi</em> demonstrates adaptive changes in stomatal architecture. Our findings emphasize the interplay between adaptation and climate, providing important insights into how plants may respond to increased droughts.</p>