Grasslands occupy as much as 40% of the Earth’s land area and represent huge ranges in both temperature and precipitation. The North American Great Plains, in particular, encompasses sizable gradients of both temperature and precipitation. Species that are widespread across the Great Plains often have morphological, physiological, and structural adaptations that allow them to respond to a varied environment. Understanding these traits can help gauge an ecosystem’s sensitivity to and robustness against future changes in climate.
In a new article published in Annals of Botany, authors Seton Bachle and Jesse B. Nippert explored the relationship between environmental variability and leaf traits using the widespread Great Plains grass, Andropogon gerardii, a species that accounts for over 70% of the annual biomass in the tallgrass prairie. The authors used fluorescent confocal microscopy to study leaves from four different sites, comparing microanatomical leaf features to climate data from each site. Features studied included xylem diameter, bundle sheath thickness, mesophyll area, and xylem wall thickness, among others.
The microanatomical traits studied showed wide variation both within and between sites, though they did not show any clear latitudinal trends. The best predictor of variability was the interaction of temperature and precipitation within a given growing season. For several traits related to carbon assimilation, such as mesophyll area, the researchers found a direct correlation to average annual temperature. No such relationship held for precipitation. Measurements related to plants’ water-use efficiency were not independent, but co-varied with one another, and showed higher regional variability.
“When individuals of A. gerardii were measured across the region, functional responses of water-use strategies illustrate a clear pattern of maximizing water transport or water storage,” write the authors. “The higher regional variability in microanatomical traits associated with water-use may facilitate populations of A. gerardii to persist through dry periods that would otherwise require decreased carbon assimilation caused by stomatal closure, degradation of photosynthetic machinery and increased water stress leading to the loss of vessel integrity or cavitation.”
Overall, the findings show how within-species variation in microanatomical traits may explain the variation in whole leaf-level traits reported across temperature gradients.