Microbial necromass carbon and nitrogen persistence are decoupled in agricultural grassland soils

Microbial necromass is an important component of soil organic matter, however its persistence and contribution to soil carbon sequestration are poorly quantified. Here, we investigate the interaction of necromass with soil minerals and compare its persistence to that of plant litter in grassland soils under low- and high-management intensity in northwest England. During a 1-year laboratory-based incubation, we find carbon mineralization rates are higher for plant leaf litter than root litter and necromass, but find no significant difference in carbon persistence after 1 year. During a field experiment, approximately two thirds of isotopically-labelled necromass carbon became mineral-associated within 3 days. Mineral-associated carbon declined more rapidly than nitrogen over 8 months, with the persistence of both enhanced under increased management intensity. We suggest that carbon mineralisation rates are decoupled from carbon persistence and that necromass carbon is less persistent than necromass nitrogen, with agricultural management intensity impacting carbon sequestration in grasslands. Different mineralization rates between plant litter and microbial necromass do not necessarily imply differences in carbon persistence, and necromass carbon is less persistent than nitrogen, according to inoculation experiments with grassland soils under high- and low-management intensity.

Automated summary

Microbial necromass is an important component of soil organic matter and plays a significant role in carbon sequestration. The persistence of carbon in necromass is lower than that of nitrogen, and agricultural management intensity has an impact on carbon sequestration.