Increasing plant species diversity stimulates soil microbial necromass nitrogen accumulation in a subtropical forest

Abstract Soil nitrogen status is tightly related to vegetation productivity and ecosystem carbon sequestration. Therefore, how increasing plant species diversity (PSD) during vegetation restoration or afforestation affects soil nitrogen pool would ultimately determine its effects on vegetation productivity and ecosystem carbon sequestration. Though diversifying plant species has been found to benefit soil nitrogen accumulation, how it influences soil microbial necromass nitrogen (MNN), which is a major constituent of soil nitrogen pool, remains unexplored. Forty‐five plots with different PSD were selected in a subtropical forest with the soil being calcareous. Soil MNN was indexed by amino sugars and microbial growth, microbial nitrogen use efficiency, and other soil biotic or abiotic variables were simultaneously measured to explore the influence of increasing PSD on soil MNN pool. Increasing PSD significantly ( p < 0.05) stimulated soil microbial growth and contents of fungal, bacterial, and total MNN, but only marginally ( p = 0.07) enhanced microbial nitrogen use efficiency. Structural equation modelling revealed that increasing PSD‐stimulated soil MNN content by enhancing microbial biomass through three paths, that is, promoting microbial growth via increasing soil nitrogen availability and the relative abundance of copiotrophic microbial taxa, increasing the inputs of plant‐derived available substrates, and improving mineral protection through elevating soil exchangeable calcium and magnesium levels. However, increasing PSD did not alter the contribution of MNN to soil nitrogen pool, likely owing to the proportional increase of plant‐derived organic nitrogen and the marginal increase in microbial nitrogen use efficiency. Synthesis and applications : These findings highlight that increasing plant species diversity is an effective measure for promoting soil microbial necromass nitrogen accumulation. Considering the importance of soil nitrogen in supporting vegetation productivity and ecosystem carbon sequestration, the current study advocates for the incorporation of diversifying plant species during vegetation restoration or afforestation.