Relationships at the aboveground--belowground interface: plants, soil biota, and soil processes

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.sub.4] vs. [C.sub.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. Key words: bacteria; C mineralization; diversity; functional groups; nematodes; nitrogen mineralization; phospholipid fatty acids (PLFA); plant richness; protozoa; resource heterogeneity; resource quality; soil ecosystem.