Land-use driven microbial community legacy shapes soil functionality

Microbial communities are central to soil ecosystem function. However, the extent to which functional diversity is conserved across communities, providing resilience to environmental change, remains uncertain. Here, we investigated how microbial legacy and soil properties shape community assembly and function, by cross-inoculating distinct microbial communities into sterilised soils from agricultural and semi-natural habitats within a 6 km radius. Over a 10-month incubation, the soil environment drove microbial community convergence at high taxonomic ranks, but fine-scale community composition and functional outcomes remained distinct. Distinct microbial communities showed a ‘home-field advantage’ in soil carbon use that increased cumulative respiration by 16-26% in agricultural soils and by 26-84% in semi-natural soils, demonstrating limited redundancy of broad ecological function between soil communities. Increased soil respiration in home-field soil communities was associated with significantly higher microbial diversity, indicating filtering selection driven by unfamiliar soil abiotic environments. Distinct communities also caused significant shifts in soil pH associated with contrasting inorganic nitrogen transformations, exposing limited conservation of specialised metabolic functions. In summary, microbial community legacy had a lasting influence on carbon and nitrogen cycling, and thus, the effects of anthropogenic land use change on soil microbial functional diversity will likely have substantial impacts on these key ecosystem processes. These findings have implications for the resilience of soil health and function under land use change and the potential for predicting the success of ecosystem restoration efforts, given the limited conservation in functional potential.