Grass harvesting eliminates the beneficial effects of legume addition on soil nematode communities in a tall grass pasture

Abstract

Legume is an important type of plant functional group that can provide a myriad of ecosystem services. In general, the legume can promote the developments of soil fertility, soil biota, and other plants due to its ability to fix nitrogen. In practice, the legume-rhizobium system is one of the most ancient and successful biotic management strategies in anthropogenic ecosystems. However, little is known about how legumes interact with other agricultural management practices and affect soil biota. In this study, a full factorial design was employed to investigate the effects of a shrubby legume (Amorpha fruticosa) addition in conjunction with grass harvesting frequency on soil nematode communities in a hybrid napiergrass (Pennisetum hydridum) pasture. There were three grass harvest frequencies as two, four, and six times annually, as well as three legume densities including no legume, low legume density, and high legume density. During two-year monitoring, the results showed that the legume addition considerably enhanced abundances of total nematodes and bacterivorous nematodes as well as metabolic activities of total nematodes, bacterivores, and omnivore-predators for production and respiration, and the effects increasing with legume density. However, increased frequency of grass harvesting eliminated the effect of legume addition on soil nematode communities. The results suggest that frequent aboveground biomass export from the ecosystem may eliminate the bottom-up control of legumes on soil biota. Our findings could provide a better understanding of legume-soil interactions.