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

Premise: Understanding how plant populations adapt to water limitation
through stomatal traits is key to predicting drought responses. The
dominant C~4 ~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 experimental
drought reduces stomatal size but increases density to maintain
photosynthesis. 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.  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. Conclusions: This study reveals
that A. gerardi 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.