University of Wyoming Laramie, Wyoming, United States
Abstract: Determining how plant communities will respond to changes in the timing and amount of precipitation is a pressing concern for regions facing rapid climate changes. However, our ability to predict community responses to drought stress is hindered by a lack of a measurable and mechanistic framework of population fitness across environmental conditions. Traits serve as quantifiable proxies for physiological trade-offs that can provide insight into the drivers of population responses. Theory suggests linking plant traits to vital rates in different conditions could provide this framework for predicting community responses to stress, but strong empirical tests are still needed. To fill this knowledge gap, we have measured the annual survival and growth of individually tagged plants for 15 mixed grass prairie species subjected to increasing levels of precipitation reduction. We use linear mixed effects models to show that the relationships between traits and fitness varied strongly with the intensity of the drought experienced and differed depending on which vital was considered. Interestingly, traits related to drought tolerance, such as leaf dry matter content, significantly predicted the likelihood of survival while traits more strongly related to resource capture ability, such as leaf nitrogen content, significantly predicted growth. Our experimental results support predictions from trait-based theories of fitness responses to drought, but simultaneously highlight the importance of considering trade-offs in trait and vital rate relationships. These findings improve our ability to predict how communities may be affected by increasing intensity of drought events and can directly inform conservation and restoration efforts by pinpointing vulnerable species and communities.
