Spatial plant resource acquisition traits explain plant community effects on soil microbial properties

Abstract

Trait-based approaches have recently been employed to develop a more mechanistic understanding of plant community effects on the assembly and functioning of terrestrial ecosystems. Despite the broad consensus that soils provide essential ecosystem services, plant community effects on soil communities and functions have rarely been linked to aboveground and belowground plant traits. Here, we studied the effects of plant species richness, plant trait diversity, and single plant functional traits related to spatial and temporal resource acquisition on soil microbial properties over five years in a grassland biodiversity experiment. The main response variables were soil basal respiration and microbial biomass. Above- and belowground plant traits associated with spatial (plant height, leaf area, rooting depth, and root length density) and temporal resource acquisition (growth start, flowering start) were selected to design communities with different levels of functional diversity as well as to calculate realized community means weighted by plant species cover. Plant species richness and trait diversity effects on soil microbial properties were nonsignificant over the course of the five-year experiment. After four years, however, we found significantly higher soil basal respiration in plant communities with smaller leaves and both denser and shallower root systems than in plant communities with taller plants and sparse root systems. One year later, these effects were significant for both soil basal respiration and soil microbial biomass. Structural equation modeling revealed that plant community effects on soil microbial properties were mostly due to differences in rooting depth, although the explanatory power of our models was low. Our findings highlight the importance of incorporating plant traits, particularly root traits, in analyses of plant community effects on soil biota and functions. Selecting for particular plant traits in communities and considering interactive effects of specific plant traits may facilitate the targeted management of grasslands to maintain essential ecosystem services.