The Response of Grassland Production to N and P Fertilizer Management Mediated soil Nematode Community in Qinghai-Tibet Plateau of China

Nitrogen (N) and phosphorous (P) fertilizer management is an effective approach to improve grasslands and feed quality following grassland degradation; however, it is still unclear how N and P fertilizer management affects soil nematodes and how this leads to changes in vegetation production. This study investigated the responses of vegetation and soil nematode communities to a 9-year fertilization (N and P) experiment in an alpine grassland in the Qinghai–Tibetan Plateau, China. The results indicated that N fertilizer significantly increased the abundance of plant parasites, whereas P fertilizer had a notably positive effect on fungivorous nematodes compared to nitrogen fertilization. The abundance of fungivorous nematodes increased following P fertilization, but the increase was not statistically significant. N fertilizer significantly reduced bacterivorous carbon biomass and the metabolic footprint of bacterivorous nematodes, while the suppressive effect of P fertilizer and N + P fertilizer on the carbon flux of bacterial channels was significantly greater than that of N fertilization alone. The functional metabolic footprints of N and P fertilizers were significantly lower than those of the unfertilized plot (CK). N fertilizer is detrimental to the increase in vegetation production following grazing prohibition, as it is mediated by the increase of plant parasite nematodes. P fertilizer, by influencing the abundance of bacterivorous and fungivorous nematodes, benefits the production of grassland ecosystems. This is because P fertilizer inhibits carbon from entering the soil food web, thereby maintaining the carbon content in above-ground biomass. Therefore, a certain level of P addition positively contributes to the recovery of above-ground productivity.