Microbial community legacy drives variation in functionality within common soil environments

The interaction between microbial communities and soil physicochemical properties is central to the function and resilience of terrestrial ecosystems. However, the relative importance of these factors in driving soil function, and the level of functional redundancy between soil microbial communities, remains poorly understood. Here, we investigate the relationship between microbial community origin and soil physicochemical properties in shaping microbial assembly and soil function. We used a sterilisation-reinoculation approach to establish novel microbial communities in soil microcosms from diverse agricultural and semi-natural habitats, and tracked microbial community dynamics and carbon cycling over a 10-month incubation. While soil properties drove convergence of community taxonomic structure at a broad taxonomic level, genus-level community composition and functional outcomes remained distinct. Specifically, novel microbial communities caused dramatic differences in soil pH and inorganic nitrogen metabolism profiles in the same host soil. Results also revealed a 'home-field advantage', where microbial communities exhibit greater carbon use in host soils more similar to their native environment, increasing cumulative respiration by 16-26% in agricultural soils and by 26-84% in semi-natural soils. Together, these results suggest that functional redundancy between microbial communities from diverse origins is limited, and that the impacts of land use change and chemical amendment on soil function are greater than previously thought.