Suppressive service of the soil food web: Effects of environmental management

Soil food webs perform the important ecosystem services necessary to maintain both agricultural productivity and ecosystem health. Higher trophic levels in soil food webs can play a role suppressing plant parasites and affecting nutrient dynamics by modifying abundance of intermediate consumers. Natural and agricultural landscapes were sampled to compare soil faunal structure. Top-down soil suppressiveness of a parasitic nematode, Meloidogyne incognita, was determined in laboratory assay. Five treatments, including two nitrogen fertilizers, two herbicides and simulated tillage were established in experimental microcosms to evaluate the effects of simulated agricultural practices on top-down suppressiveness. Soil food web indices, based on the composition of the nematode fauna, were calculated to infer soil food web condition. Long and complex soil food webs in natural areas, with more trophic links and abundant predatory nematodes, effectively suppressed plant–parasite populations, while disturbed communities in agricultural soils did not. Soil suppressiveness was related to the ratio of predators to prey and to the prevalence of omnivore and predator species. Agricultural management led to a reduction in the suppressive capacity of the soil food web. Abundance of predatory nematodes was related to soil NH4+, probably due to excretory products of nematodes and other organisms grazing on microbes. Soil suppressiveness, soil food web dynamics and agricultural management are strongly inter-related.