Variations in microbial residue carbon and its contribution to soil organic carbon after vegetation restoration on farmland: The case of Guinan County

Microbial residue carbon (C) serves as a significant source of soil organic carbon (SOC). However, the contribution of microbial residue C to SOC accumulation after the restoration of farmland vegetation remains unclear, making it challenging to comprehend the role of microorganisms in the accumulation and transformation of SOC after vegetation restoration on farmland. Based on field investigations in Guinan County, Qinghai Province, our study focused on the microbial residue C content and its contribution to SOC in farmland, grassland, and shrub forest, employing the analysis of biomarkers. The results indicated that the microbial residue C content increased with the rise of SOC, soil total nitrogen (STN), and enzyme activities. Compared to farmland, grassland displayed significantly lower levels of SOC and STN, leading to reduced microbial residue C content, notably impacting the C content of fungal residues. Despite slightly lower levels of SOC and STN compared to farmland, shrub forest exhibited higher soil microbial residue C content, notably within bacterial residue C, due to elevated soil enzyme activities. The contribution of microbial residue C to SOC decreased as SOC content increased. In farmland boasting higher SOC content, the contribution of microbial residue C to SOC was notably lower compared to shrub forest and grassland with lower SOC content. In conclusion, compared to farmland, both shrub forest and grassland exhibited higher contributions of microbial residue C to SOC, which is favorable for the sequestration of stable SOC.