Short-term impacts of aboveground herbivory (grasshopper) on the abundance and 14C activity of soil nematodes in conventional tillage and no-till agroecosytems

Abstract

This study was designed to monitor the responses of soil nematodes to different levels of aboveground herbivory and to test the hypothesis that the low level of aboveground herbivory facilitates soil nematode activities and high herbivory suppresses soil nematode activities. Three herbivory levels were established by introducing four pairs, two pairs and no grasshoppers to graze on corn plants ( Zea mays) for 2 h. The experiment was conducted in conventional tillage (CT) and no-till (NT) agroecosystems at Georgia piedmont. In NT, bacterivorous and fungivorous nematode numbers were more abundant 24 h after herbivory treatment at high grazing level compared to controls, but this was not observed at low grazing level. In NT, the 14C activity of soil nematodes was significantly higher at both low and high grazing levels than the controls. In CT, however, we did not observe any effects caused by aboveground herbivory on the abundance and 14C activity of soil nematodes. The abundance of other trophic groups of soil nematodes (phytophages, predators and omnivores) was not affected by aboveground herbivory treatments under either NT or CT regimes. The curvilinear relationship between the nematode activity and the grazing intensity was not found in this study, we suggested that a grazing gradient of leaf area loss ranging from 0 to 100% might be more desirable for future research. We hypothesized that root associated materials might be more important to soil organisms in NT than in CT since the effect of aboveground herbivory on soil nematodes was only observed in NT.