University of Nebraska-Lincoln Lincoln, NE, United States
Abstract: Plant functional traits show extensive intraspecific variation, and understanding this variation is essential to using these traits effectively and reliably in ecological research and analyses. A potentially important, though rarely studied, component of intraspecific variation is variation over time. At our western Nebraska study site, grassland plant species show year to year trait variation greater than their variation in response to nitrogen addition. The patterns of variation appear consistent with rainfall driven responses, with more acquisitive leaf economics spectrum trait values occurring in high rainfall years. Thus far, however, this connection has been supported only by observational comparisons across a small number of study years.
In this study, we sought to test the effects of rainfall variation on species’ functional traits experimentally. To do so, we used rainfall shelters and rainfall addition treatments to manipulate water availability in factorially combined set of rainfall and nutrient treatment plots. In these plots, we collected functional trait data on seven common plant species over two study years. We found that rainfall manipulation significantly altered two of our four study traits, specific leaf area and leaf dry matter content, with water addition leading to more acquisitive trait values. However, the effect sizes of the water treatments were less than half the effect sizes of sampling year. The remaining traits, plant height and chlorophyll content, showed no consistent responses to rainfall treatment.
These results lead us to conclude that total rainfall is one component in a broader array of variables driving year to year trait variation. Though factors unrelated to rainfall may contribute, it is likely that other aspects of rainfall variation, such as intervals between rainfall events and changes to vapor pressure deficit also play important roles. The relative weight of these variables will likely vary with the species, site, and trait considered.
