Carbon mineralization and microbial activity in agricultural topsoil and subsoil as regulated by root nitrogen and recalcitrant carbon concentrations

aimsmechanisms of subsoil carbon sequestration from deep-rooted plants are elusive, but may contribute to climate change mitigation. this study addressed the role of root chemistry on carbon mineralization and microbiology in a temperate agricultural subsoil (60 and 300 cm depth) compared to topsoil (20 cm depth). methods:roots from different plant species were chemically characterized and root-induced co2 production was measured in controlled soil incubations (20 weeks). total carbon losses, β-glucosidase activity, carbon substrate utilization, and bacterial gene copy numbers were determined. after 20 weeks, resultant carbon mineralization responses to mineral nitrogen (n) were tested. results:root-induced carbon losses were significantly lower in subsoils (32–41%) than in topsoil (58%). carbon losses varied according to root chemistry and were mainly linked to root n concentration for subsoils and to lignin and hemicellulose concentration for topsoil. increases in β-glucosidase activity and bacterial numbers in subsoils were also linked to root n concentration. added mineral n preferentially stimulated co2 production from roots with low concentrations of n, lignin and hemicellulose. conclusion:sthe results were compatible with a concept of n availability and chemically recalcitrant root compounds interacting to control subsoil carbon decomposition. implications for carbon sequestration from deep-rooted plants are discussed.