Drought alters resource-allocation trade-offs in a dominant grass

Photo Credit

USDA-ARS photo by Philip A. Fay

Impacts of precipitation on photosynthesis.

Precipitation can impact correlations between leaf functional traits and associations between these traits and gene expression. The leaf traits that determine plant performance often evolve together in response to environmental conditions—a quick-return on investment strategy of fast-growing, short-lived, high-nutrient leaves is often advantageous in resource-rich environments where acquisition of more resources is paramount, while a slow-return on investment strategy of slow-growing, long-lived, low-nutrient leaves is often advantageous in resource-poor environments where conservation of resources is necessary. Because the traits and trait combinations that are most advantageous can change with environmental conditions, trade-offs may limit the habitats in which a particular functional strategy can succeed. 

Precipitation can impact correlations between leaf functional traits and associations between these traits and gene expression. Despite strong evidence for some functional trade-offs at broad geographic and taxonomic scales, few studies have examined the major drivers of these trade-offs within species—phenotypic plasticity and standing genetic variation. In a dominant warm-season tallgrass species, switchgrass, we show that both phenotypic plasticity—changes in traits in response to the environment—and standing genetic variation—differences in the genetic basis of traits among plants—contribute to functional strategies. 

Furthermore, functional strategies were more consistently expressed when plants received ample water than when they were subjected to drought: selection favored certain trait combinations (e.g., low nitrogen content and high leaf structural costs) in wetter environments; in drier environments, selection favored only individual traits (e.g., higher photosynthetic rates) rather than trait combinations. This suggests that some aspects of plant functional strategies are more drought-sensitive than others, breaking down in more stressful environments. Understanding how plants exhibiting different functional strategies perform across environments may improve our ability to select plant varieties to maintain productive grasslands.