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

PREMISE: grass Andropogon gerardi, 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 that experimental drought reduces the size of stomata but increases their density to maintain photosynthesis. METHODS: 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. Eight populations (precipitation: 472-1356 mm yr⁻¹) were then subjected to drought (~15% moisture) or were well-watered (30% control) to assess trait plasticity. Stomatal traits were measured using epidermal peels and light microscopy, gas exchange with a LI-COR 6400, and network analyses were used to characterize adaptive strategies. RESULTS: Arid populations exhibited smaller, denser stomata compared to wet populations, and networks demonstrated a trade-off between stomatal size and density. In the 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. CONCLUSIONS: Andropogon gerardi demonstrated 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.