Long-term fertilization effects on soil biotic communities are mediated by plant diversity in a Tibetan alpine meadow

Plant diversity is assumed to positively influence the diversity of soil biota. However, empirical studies on the linkages between diversities of plants and soil biota under fertilization revealed inconsistent results. In addition, the relative importance of direct and indirect impacts of fertilization on plant and soil biotic communities is still unclear. Taking advantage of a 13-year fertilization experiment with nitrogen and phosphorus addition in an alpine meadow, we measured community composition of plants, bacteria, fungi, and nematodes, analyzed direct and indirect effects of fertilization on these communities, and investigated relationships between their community structures. We found that fertilization significantly increased plant biomass and nematode abundance, and decreased their α-diversities. Microbial biomass carbon and fungal α-diversity increased with low levels of fertilization but decreased at the highest level of fertilization. However, structural equation modelling showed that fertilization had minor direct effects on soil biota except for bacteria. Instead, fertilization indirectly influenced fungi and nematodes through plant α-diversity. Furthermore, β-diversity (community dissimilarity) was positively correlated between plants and soil biota, even after controlling for fertilization effects. Our study provides empirical evidence showing the linkage of both α- and β-diversities between plants and soil biota, and implies the potential of plants for regulating soil biotic communities under long-term fertilization. These findings can help us predict changes in soil biota under nutrient-enrichment scenarios in alpine meadows with data on plant diversity and community composition.