Interaction between maize residues and initial soil carbon status on soil labile organic carbon pools

Abstract

Crop residue serves as a vital source of energy and nutrients for microbial proliferation, ultimately contributing to the formation of soil organic carbon (SOC). Labile organic C pool (i.e., extractable organic C and microbial biomass C) not only represents a small part of SOC, but also is a sensitive indicator of soil biogeochemical process under agricultural management. However, the interaction between maize residue types and initial soil C status on the fate of residue C in labile organic C pools remains not very clear. Here, we added the ¹³C-labeled maize root, stem, and leaf residues into soils with low and high initial C status for 360 days of incubation and analyzed the contents of residue derived- salt-extractable organic C (SEOC) and microbial biomass C (MBC). The results showed that average 7.31 % and 6.46 % of SEOC was derived from maize residue C in the low and high C soil during the whole incubation, respectively. The contribution of MBC derived from residue C to total MBC in the high C soil was on average 13.36 % higher than that in the low C soil, which indicated that the high C soil could accelerate the transformation of residue C into microbial biomass by efficient anabolism pathway. The distribution percentage of leaf residue C to MBC was on average 1.73 % higher than those of root residue C and stem residue C to MBC in the low C soil, whereas more root residue C was entered to SEOC and MBC compared with stem residue C and leaf residue C in the high C soil, which demonstrated that the low-quality residue (i.e., maize root) tended to be more susceptible to microbial utilization, but it depended on the initial soil C status. Overall, these findings contribute to understanding the mechanisms of microbial-mediated C transformation processes, and provide insights into the capture and incorporation of plant residue C into labile organic C pools driven by initial soil C status and crop residue returning.