The asynchronous response of structure and functionality of soil nematode community to Tibetan sheep grazing in an alpine grassland on the eastern Qinghai-Tibet Plateau

Over the past three decades, the degradation of alpine grasslands on the Qinghai-Tibet Plateau caused by overgrazing has been investigated extensively. Nevertheless, our understanding of belowground degradation remains insufficient compared to that of aboveground degradation, which hinders our comprehensive understanding of the degradation process. Because nematodes play a critical role in the soil-food web and are sensitive to environmental changes, assessing the nematode community helps to reveal belowground responses to grazing. We conducted a manipulated grazing experiment in the alpine grassland around the Qinghai Lake Basin in the eastern Qinghai-Tibet Plateau, which included four grazing treatments: no grazing, light grazing, moderate grazing, and heavy grazing, to explore the effects of grazing intensity on the structure and functionality of soil nematode communities. The community total abundance and genus richness declined with soil depth; however, the proportion of nematodes in the subsoil was 28.6%. Heavy grazing decreased the total abundance by 17%, mainly through the decrease of common genera with relative abundances between 1% and 10%. Heavy grazing enhanced the relative abundance dominance of two dominant genera (relative abundances >10%, Acrobeloides and Aporcelaimellus), but showed different trends with grazing intensity. The dominance of Acrobeloides increased with increasing grazing intensity, whereas that of Aporcelaimellus decreased. The nematode community's structural composition and functionality (enrichment index) responded asynchronously to heavy grazing, with a greater response in community structure than in functionality. Therefore, soil nematodes should be considered when studying the mechanisms of grassland degradation and restoration.