Management of soil microenvironment and microbial community assembly for carbon accrual in agricultural soils

Agricultural intensification has led to loss of soil organic carbon (SOC). Restoring SOC offers an opportunity to help mitigate climate change. Soil microbes are responsible for transforming plant materials into stable forms of SOC; our previous results suggest that microbes in temperate pristine grassland soils especially support this process due to their high carbon use efficiency. Grassland microbes could therefore be recruited to help restore SOC in degraded soils. To examine this, we established a lab mesocosm study where we reciprocally transferred microbes derived from undisturbed grassland soil and neighbouring cropland soil into their sterile counterparts, collected at two UK sites. Mesocosms received regular organic inputs and were incubated for 8 months after which 16S-rRNA/ITS sequencing was performed to assess microbial community assembly and SOC was measured. SOC outcomes were shaped by the interaction of microbial inoculum and soil microenvironment, with assembly of fungi influenced more by inoculum while that of bacteria influenced more by microenvironment. Carbon loss was higher in soils with cropland inoculum compared to those with grassland inoculum. Introduction of grassland inoculum into cropland soils resulted in higher fungal diversity with better SOC outcomes. We speculate that this is due to creation of higher fungal necromass that is more persistent when stabilised onto minerals. Overall, our findings suggests that environmental filtering through land management-driven promotion of favourable soil properties could be fundamental to microbe-driven SOC accrual while introduction of diverse fungal taxa could also help build SOC. Integrating soil management and microbial interventions can promote carbon accrual.