Tree mycorrhizal associations strongly mediate soil microbial β-diversity along an elevational gradient in a warm-temperate forest

Determining the factors influencing the elevational gradient of soil microbial diversity is a fundamental yet unresolved aspect of microbial ecology. Despite the considerable research on soil microbial β-diversity patterns across elevations, there has been limited attention given to the importance of symbiotic biotic relationships, e.g. tree mycorrhizal associations. Here, five-point samplings and metagenomic approaches were used to investigate the soil microbial β-diversity in 15 permanent forest sites (400 m²) along an elevational gradient ranging from 894 to 2219 m in Mt. Zhongtiao, a warm-temperate forest region in China. We also measured tree mycorrhizal associations characteristics, soil physiochemical characteristics, and plant diversity to gain a comprehensive understanding of the factors that influenced the microbial communities in this region. Our findings revealed an overall decreasing trend in the β-diversity of soil bacteria and fungi with increasing elevation, with tree mycorrhizal associations emerging as dominant explanatory factors for elevational patterns of microbial β-diversity. The decline in abundance of EcM (Ectomycorrhizal) tree species, the rise in the EcM/AM (Arbuscular mycorrhizal) ratio, and the overall basal area of EcM tree species emerged as the primary factors driving microbial β-diversity, and generally explained over 20 % variations of elevational microbial β-diversity. Importantly, the composition of tree species mycorrhizae influenced fungal β-diversity more than bacterial β-diversity (0.391 > 0.266). Furthermore, the influence of tree mycorrhizal associations on the elevational distribution of soil microbial communities was observed, either directly or indirectly mediated by soil physicochemical properties. The indirect effects of tree mycorrhizal composition on species β-diversity were both greater than the direct effects on bacteria (0.433 > 0.266) and fungi (0.391 > 0.245). These results underscore the importance of considering tree mycorrhizal associations in explaining variations in elevational patterns of soil microbial community structure, providing insights into the mechanisms driving these variations.