Genotypes of a dominant tallgrass species vary in their response to changes in precipitation means and variability

Background/Question/Methods

Alterations in both means and variability of precipitation regimes are forecast with global climate change. These changes may impact genotype composition of populations by selecting for those genotypes that can better cope with the novel climatic conditions. However, it remains unclear which traits are important for tolerating precipitation change and for allowing genotypes to persist. To address this issue, we assessed how changes in both the size and variability of watering events affected the growth and leaf level physiology of five common genotypes of the C₄ grass, Andropogon gerardii, which were previously found to be differentially affected by alterations in precipitation regimes in an ongoing climate change field experiment at the Konza Prairie Biological Station in northeastern KS. In a full factorial greenhouse experiment, for all genotypes, we imposed three watering amounts (Konza Prairie growing season average, 40% decrease, and 60% increase) and two watering frequencies (every 5 or 10 days). During the experiment we measured photosynthesis and stomatal conductance before and after a watering event and height monthly.

Results/Conclusions

Amount and variability of water events and genotype identity affected plant growth and leaf-level ecophysiology. Plant height differed among genotypes and was also affected by the amount and timing of watering events. Maximum photosynthetic rate and stomatal conductance both before and after watering events were affected by genotype, water amount, and timing between watering events. There was an interaction between genotype and water amount over time when measurements were made before a watering event, however not afterwards. The lack of a genotype by water amount interaction after the watering events suggest that differences in the response of genotypes to water limitation are more pronounced than when water is not limiting. The ability of a plant to recover photosynthetic rates after a watering event was affected by water amount, variability, and genotype identity. Some genotypes were better at recovering photosynthetic rates after a watering event, while others maintained steady levels of photosynthesis irrespective of water availability. Overall, genotypes do differ in their response to water stress, with evidence that some genotypes are better adapted to low soil moisture conditions and others to more variable rainfall patterns. This has important implications for understanding how novel climates will alter genotypic structure of populations.