Response of soil microflora to changes in nematode abundance - evidence for large scale effects in grassland soil

The effect of increasing nematode abundance on microbial biomass and activi ty in a temperate grassland soil was investigated in a microcosm experiment . The experiment lasted for 33 days. The natural nematode diversity, as wel l as relevant aspects of the spatial heterogeneity of the soil microhabitat in a 80 m(2) sampling area were maintained in the microcosms. No correlation was found between nematode abundance and microbial biomass ( CFE) or ergosterol content (as a measure of active fungal biomass). However , a doubling of nematode abundance reduced CO2 production by 11% and increa sed bacterial substrate utilization (BIOLOG) by 18%. A possible explanation is that fungal activity was strongly reduced at higher nematode density, o vercompensating the simultaneous increase in bacterial activity. The results show that the nematode community in a grassland soil is capable of causing a considerable shift in soil microbial activities towards an in creased bacterial metabolism, overriding the spatial heterogeneity of the s oil habitat and the taxonomic diversity of the community itself, and thereb y producimg functional effects relevant at spatial scales that exceed the a ctivity domains of the organisms involved.