Soil foodwebs in agroecosystems: impacts of herbivory and tillage management

Soil rhizospheres are one of the principal 'hotspots' of terrestrial ecosystems. Using isotopic 14 carbon (C-14) tracer techniques, we measured impacts of aboveground herbivory on rhizosphere microbial growth and subsequent repercussions in an agroecosystem detrital foodweb. Soil microarthropods in conventionally tilled (CT) agroecosystems accumulated more radiocarbon tracer than in no-tillage ones (NT), reaching concentrations as high as those in the roots. Nematodes, in contrast, accumulated more tracer in the NT systems, possibly reflecting the greater proportion of label going initially to bacterial communities in the rhizospheres. With a simulation model of the decomposition of C-14-labeled litter, we evaluated the relative contributions of bottom-up and top-down forces in the detrital foodweb. Microbial biomass was more resource-regulated, and microbivorous fauna (nematodes, protozoa, microarthropods) was more sensitive to second- and third-order predators in the system. (C) 2002 Editions scientifiques et medicales Elsevier SAS. All rights reserved.