Dry–wet cycles promoting the accumulation of microbial necromass and mineral associated organic carbon after wheat straw and nitrogen co-addition

Soil organic carbon preservation is crucial for mitigating global warming and achieving sustainable agricultural development. However, little is known about how dry–wet cycles impact stable soil organic carbon fraction such as mineral associated organic carbon (MAOC) and microbial necromass carbon after wheat straw and nitrogen co-addition.

To address this gap, we conducted an indoor incubation experiment including control (CK), ammonium nitrogen addition (N), wheat straw addition (Straw), wheat straw and N co-addition (Straw + N) under constant water content or four dry–wet cycles. The dynamic change of soil respiration, MAOC as well as bacterial and fungal necromass carbon was monitored during each dry–wet cycle.

Compared to constant water content, dry–wet cycles decreased the cumulative emission of soil respiration CO₂-C in Straw + N by 10.80%. Compared to CK, MAOC increased by 149% and 123% in Straw and Straw + N groups under dry–wet cycles, respectively, which was more prominent than constant water content. Moreover, compared to CK, bacterial necromass carbon raised by 60.20% in Straw + N under dry–wet cycles, which was the highest among all groups. Fungal necromass carbon didn’t change in Straw + N under dry–wet cycles, but decreased under constant water content or in Straw groups. Random forest and correlation analysis suggested that MAOC was mainly formed via ex vivo pathway by adsorbing dissolved organic carbon after straw addition.

Our study demonstrates that the incorporation of straw and nitrogen addition has the potential to enhance agricultural soil organic carbon sequestration by inhibiting soil respiration and rising stable organic carbon stocks under dry–wet cycles.