Divergent assembly patterns of Minjiang fir root-associated fungal and bacterial communities are regulated by habitat conditions
Root-associated microbial communities play important roles in mediating plant growth, health, and environmental adaptability. However, it remains unknown which microbial taxa possibly help host fitness underlying the host niche and how root-associated microbial assembly patterns are associated with the host niche. Here, we investigated the bacterial and fungal communities of three spatial compartments (bulk soil, rhizosphere and endosphere) associated with Minjiang fir (Abies fargesii var. faxoniana, an important endemic species of subalpine forests in western Sichuan, China), saplings between suitable habitat (SH, within the fir niche range) and unsuitable habitat (unSH, outside the fir niche limitation). Host fitness-related habitat conditions obviously regulated microbial communities regardless of the spatial compartment and microbial taxa. Host fitness-related habitat conditions shifted root-associated (rhizosphere and endosphere) microbial compositions, notably by increasing the relative abundance of the growth-promoting bacteria Burkholderia and mycorrhizal fungi Cortinarius and Piloderma in the suitable habitat. The fungal and bacterial beta diversity responded differently to habitat conditions, with higher fungal endemism and lower bacterial endemism while indirect habitat-dependent modulations for bacteria by regulating soil properties. Host fitness-related habitat conditions altered the root-associated microbial response to soil and plant differences, with higher contribution of soil properties to root-associated microbial variations in unsuitable habitats than in suitable habitats while lower contribution of plant traits to endospheric microbial variations in unsuitable habitats. Our findings improve understanding of plant fitness underlying species niches from microbiome perspectives by underscoring diverse belowground community assembly patterns depending on habitat conditions. Thus, forest management needs to consider host habitat conditions associated with host niches in order to enhance microbial function.