PS 62-40
Variation in drought response thresholds: Physiological responses of genotypes of a dominant C4 grass to a range of soil moisture conditions
Intra-specific genetic diversity of dominant plants directly relates to ecosystem function, driving community responses to climate extremes, such as drought, through changes in the genetic structure of populations. These changes in genetic structure will be determined by differential abilities of genotypes to cope with increased water stress. The dominant C4 grass species in tallgrass prairie, Andropogon gerardii, is well-suited for assessing how genotypes may differ in their ability to cope with drought. As soil water content (SWC) approaches 15%, photosynthetic capacity of A. gerardii begins to rapidly decline, however it is unclear whether this drought threshold of physiological activity varies among genotypes. We selected five genotypes of A. gerardii previously shown to fluctuate in abundance with increased water stress. Individuals of the five A. gerardii genotypes were grown in a greenhouse study under eight different SWC levels ranging from <10% to 40%. Clonally propagated individuals were acclimated to the greenhouse environment for four weeks, followed by physiological measurements (including net photosynthesis, stomatal conductance, and leaf water potential) taken every week over four weeks, allowing us to determine the onset of physiological stress and variability among genotypes. Leaf tissue was collected to assess quality and quantity of RNA for future work involving gene expression differences among genotypes.
Results/Conclusions
Two genotypes (“G1” and “G4”), found more often in rainfall manipulation plots, maintained higher photosynthetic rates, higher conductance, lower water potentials, and high RNA quality until 10% SWC, after which function declined rapidly. These results differed significantly from “G2” and “G3” which declined in function and RNA quality after 20% SWC. “G11” did not differ from either of these two groups, but showed a more gradual decline in function and RNA quality at approximately 15% SWC. “G2” and “G3” demonstrated earlier onset of stress than other genotypes (three weeks versus four weeks), although differences were not significant. These results suggest that A. gerardii genotypes differ in their drought response and thresholds of physiological function decline. This variation in drought response among genotypes of the dominant grass could have important implications for maintaining ecosystem function across a wide range of soil moisture conditions. Further study of intra-specific diversity is crucial; management of ecosystems under climate change scenarios will require an understanding of important genotypes of dominant species. Additionally, understanding the diversity of drought resistant A. gerardii genotypes could improve plant breeding in closely related agricultural and biofuels species.