Calcium promotes persistent soil organic matter by altering microbial transformation of plant litter

Abstract

Abstract Calcium (Ca) can increase soil organic carbon (SOC) persistence by mediating physico-chemical interactions between organic compounds and minerals. Yet, Ca is also crucial for microbial adhesion, potentially affecting colonization of plant and mineral surfaces. The relative importance of Ca as a mediator of microbe-mineral-organic matter interactions and resulting SOC transformation has hereto been overlooked. We incubated 44Ca labeled soils with 13C15N labeled leaf litter to study the effects of Ca on microbial transformation of plant litter and formation of mineral associated organic matter. Ca additions promoted hyphae-forming bacteria, which often specialize in colonizing surfaces, increased incorporation of plant litter into microbial biomass by 20% and carbon use efficiency by 40%, and reduced cumulative CO2 emission by 5%, while promoting associations between minerals and microbial byproducts of plant litter. These findings expand the role of Ca in SOC persistence from solely a driver of physico-chemical reactions to a mediator of coupled abiotic-biotic cycling of SOC.