Degradation of wild fruit forests created less diverse and diffuse bacterial communities decreased bacterial diversity, enhanced fungal pathogens and altered microbial assembly in the Tianshan Mountain, China

Wild fruit forests are vital reservoirs of germplasm genetic and biodiversity. Unfortunately, wild fruit forests of Central Asia are in the decline due to fungal disease and insect pest outbreaks. A health soil microbial community may help ameliorate the degradation of wild trees by increasing their systematic resistance, stabilizing soil carbon pool, and maintaining the quality of the habitat environment. We evaluated soil bacterial and fungal community beneath the dominant tree species, Malus sieversii (Ledeb.) M. Roem, to identify potential interactions between wild fruit forest degradation events and soil microorganisms in the Tianshan Mountain, China. Based on targeted metagenomics of the 16S rRNA and ITS (Internal Transcribed Spacer), we explored the bacterial and fungal microbial communities in soils beneath healthy and degraded M. sieversii trees (i.e., microbial biomass, species interactions, potential and niche breadth), and soil physicochemical properties. We found that the degradation of M. sieversii reduced the beta diversity of topsoil bacterial communities and fungal symbiotic groups. The decline in M. sieversii abundance loosened connections within bacterial and fungal co-occurrence networks. Community assembly identified higher migration rates in the topsoil around degraded M. sieversii for bacteria and for fungi, suggesting that dispersal restricted in degraded wild fruit forest soils. Ultimately, the demise of M. sieversii homogenized the soil bacteria resulting in a narrow niche-breadth, enhanced pathogenetic fungal species, and reduced beneficial symbiotic and saprotrophic fungal diversity. Our results demonstrated that the degradation of M. sieversii leads to alterations in diversity, self-assembling and resource competitiveness of forest soil-dwelling microorganisms.