For many grassland species, water availability is a key driver of physiological functioning. Coexisting species utilize a variety of strategies to tolerate or avoid periodic drought occurring during the growing season. Plant traits are regularly utilized to infer species responses to environmental variability and ecological processes. For example, species with the C4 photosynthetic pathway exhibit an increased photosynthetic rate while maintaining a high water-use efficiency. In the Central Great Plains of North America, four C4 grass species are responsible for the majority of aboveground net primary productivity. Leaf physiological and anatomical traits may provide greater insight into species-specific productivity across spatial and temporal gradients of water availability.
We measured key physiological and morphological traits associated with drought tolerance in an effort to quantify trait plasticity across a geographic rainfall gradient and over time among four phylogenetically similar C4 grass species. Leaf-level physiological traits include gas exchange and chlorophyll fluorescence. Leaf-level morphological traits were measured via cross-sectional microscopy.
We asked three inter-related questions. Can small-scale anatomical traits help explain variability in whole-leaf physiology? Are species –specific trait relationships constant among genotypes across a broad geographic gradient? Do seasonal changes in leaf phenotype alter physiological-anatomical trait relationships for these four grass species?
Differences between major C4 grasses were observed both physiologically and morphologically within a growing season and between locations in Kansas. Although leaf physiological traits are more variable compared to morphology, small-scale anatomical traits are statistical predictors of whole-leaf physiology. For example, bundle sheath area correlates to whole-leaf photosynthetic rates for each species measured. Species-specific trait relationships vary minimally across the geographical gradient. Physiological and anatomical trait relationships remain correlated over the course of the growing season, with subtle variation among sites along the rainfall gradient. This research illustrates that species hold specific leaf morphology that help explain its physiology. Identifying linkages between leaf physiological and anatomical traits may provide greater insight into population and ecosystem processes across gradients of water availability, and may aid in our ability to predict ecological responses to future climate changes.