Species-specific trait-environment relationships among populations of widespread grass species

Intraspecific trait variation can be substantial and is driven by many factors. To develop predictive models of intraspecific trait variation, an understanding of the drivers of that variation is essential. At fairly broad scales, differences in the environment are expected to drive genetic variation in functional traits among populations. To isolate this genetic variability, we conducted a greenhouse common garden experiment using nine grass species native to the western United States. We assessed relationships between several root, leaf, and whole plant traits and a number of environmental conditions from the source population locations, including aspects of temperature, precipitation, vapor pressure deficit and soil moisture. We tested the hypotheses that (1) above- and belowground functional traits vary significantly within and among species, and (2) trait-environment relationships among populations of a species are consistent among species. First, we found that trait variation between species ranged from 13 to 77%, while trait variation within species ranged from 11 to nearly 39%. Traits related to overall plant size and growth rate exhibited the greatest intraspecific variation, and root traits the least variation. Second, while we found significant trait-environment relationships, they were highly variable among species. The magnitude of intraspecific trait variability found in this study indicates significant local adaptation with respect to specific trait-environment combinations, but that characterizing trait-environment relationships requires species-specific measurements and models.