Grassland management history affects the response of the nematode community to changes in above-ground grazing regime

Changes in grassland management induce disturbances that influence both soil functioning and soil fauna. This study aimed at determining the extent to which the composition of a grassland soil nematode community could be altered by a shift of grazing regime and the potential feedback that these alterations could provoke on grassland functioning. Therefore, we monitored the composition of the soil nematode community (i.e., plant-, bacterial-and fungal-feeders, omnivores and carnivores) of mesocosms that were sampled from two contrasted long-term field trials (high vs low grazing treatments) and subsequently subjected to high or no grazing for 2 years. The soil nematofauna responded faster and more strongly to the application of an intensive grazing regime on a previously extensively exploited system than the other way round. The application of an intensive grazing regime induced a significant increase in numbers of bacterial feeders and a decrease of the relative abundance of fungal-feeding nematodes. The nematofaunal community structure was determined by both the past and current grazing regimes throughout the 2 years of monitoring. Observed effects on soil microbivores seemed to reflect the 'immediate' above-ground primary production potential and to follow micro-organism dynamics. On the other hand, observed effects on root-feeding nematodes seemed to reflect the integral effect of past and current grazing regimes on plant community root biomass and quality.