Interactions at the aboveground-belowground interface provide important feedbacks that regulate ecosystem processes. Organisms within soil food webs are involved in processes of decomposition and nutrient mineralization, and their abundance and activity have been linked to plant ecophysiological traits such as species identity and the quality and quantity of plant tissue. We tested aboveground-belowground diversity relationships in a naturally developed plant community of native tallgrass prairie by taking soil samples from beneath naturally established grass tillers of chosen characteristics (e.g., homogeneous vs. heterogeneous plant combinations or C 4 vs. C 3 photosynthetic pathway) without imposing any disturbances to existing plant-soil relationships. The goal of this study was to elucidate the consequences, for soil microbiota (microflora phospholipid fatty acids, protozoa, and nematode functional groups) and for C and N mineralization, of plant community properties such as species richness, resource quality, resource heterogeneity, species identity, and presence of exotics. None of the biotic or abiotic soil variables was related to plant resource heterogeneity. Protozoa were not responsive to any of the plant community traits. Some bacterial and nematode groups were affected by plant characteristics specific to a particular plant species, but no uniform pattern emerged. Invasive and native plants generally were similar with respect to soil variables tested in this study. The lack of clear responses of soil variables to plant community traits indicates that idiosyncratic effects dominate both at the plant and soil biotic level and that generalized plant and soil diversity effects are hard to predict.

Grasslands are often characterised by small‐scale mosaics in plant community composition that contribute to their diversity. Although above‐ and belowground biota can both cause such mosaics, few studies have addressed their interacting effects. We studied multi‐trophic interactions between aboveground vertebrate grazers, subterranean ants, plant‐pathogenic soil biota (especially nematodes) and the vegetation in a temperate grassland. We found that when rabbits and cattle locally omit vegetation patches, yellow ants (Lasius flavus) respond to the taller vegetation by digging up more sand from deeper soil layers (hence making taller nest mounds), probably to maintain sufficiently high soil temperatures. We found that this ant digging affects other soil biota, as the mounds contain fewer plant‐parasitic and fungivore nematodes. Also, the mounds have lower moisture content and soil bulk densities, and higher pH and available nutrient content than the directly surrounding soil. The clonal sedge Carex arenaria grows vigorously on the mounds, producing more shoots and shorter rhizome internode lengths than in surrounding vegetation. Other plant species, such as the grass Festuca rubra, dominate the surrounding vegetation. A greenhouse bioassay experiment revealed that harmful soil organisms (as plant‐parasitic nematodes and pathogenic fungi) outweighed the effect of beneficial organisms (e.g., mycorrhizae) in this system. Rhizome biomass and shoot production of C. arenaria were indeed inhibited less by biota in soil from ant mounds than by biota in soil from the surrounding vegetation. However, the total biomass production of C. arenaria was inhibited as strongly in both soil types. F. rubra was inhibited more strongly by biota in the surrounding soil. We suggest that various direct and indirect interactions between above‐ and belowground biota can contribute to community mosaics and hence diversity in grasslands.