Soil Abiotic Properties Shape Plant Functional Diversity Across Temperate Grassland Plant Communities

There is increasing awareness that plant community functional properties can be an important driver of ecosystem functioning. However, major knowledge gaps exist about how environmental factors, especially climate and soil abiotic properties, shape plant functional diversity at a regional scale. Furthermore, at those scales the relationships between plant functional and taxonomic diversity have rarely been considered. Here, we used a large database of plant species and functional trait data from 180 temperate grasslands across England, covering a broad range of grassland types, climatic conditions and management intensities, the last having a strong influence on multiple soil variables. Our specific aims were to: (1) identify the dominant environmental factors explaining variation in different facets of plant community functional properties, including community weighted means (CWMs) of functional traits and various multi-trait functional diversity indices; and (2) test whether the relationship between plant functional and taxonomic diversity is mediated by environmental factors at a regional scale. We found that soil abiotic properties (pH and nutrient stocks), but not climate, were the main environmental factors explaining grassland plant functional diversity at a regional scale, with a significant contribution of soil nutrient stoichiometry (N/P ratio). Two indices of plant community functional properties, namely CWMs of specific leaf area and relative growth rate, were explained by interactions between soil pH and N and mean annual precipitation, soil pH soil N and soil N/P ratio. These indices were also negatively related to taxonomic diversity under certain soil abiotic conditions, specifically high soil clay content, pH and N/P. Together, our results indicate that soil abiotic properties rather than climate factors shape plant functional diversity across temperate grassland plant communities at a regional scale. They also suggest that interactions between environmental factors play a significant role in shaping patterns of plant community functional properties. Our findings are of importance for the design and interpretation of future studies using trait and diversity measures as proxies of ecosystem services at regional scales.