Divergent contribution of microbial- and plant-derived carbon to soil organic carbon in Moso bamboo forests left unmanaged

[Display omitted] •Unmanaged Moso bamboo forest duration significantly affects plant-derived C content.•Leaving unmanaged for 7–10 and 11–14 years significantly affected microbial-derived C content.•Soil cation exchange capacity dominated the accumulation of plant-derived C.•Plant biomass soil nutrients dominated the accumulation of microbial-derived C. Moso bamboo (Phyllostachys pubescens) has a high carbon (C) sequestration capacity that can help mitigate global climate change. However, owing to strengthened environmental protection policies and rising labor costs, large areas of Moso bamboo forests have been left unmanaged after long-term intensive management. Consequently, the contribution of plant- and microbial-derived C as part of soil organic carbon (SOC) has not been reported in Moso bamboo forests. Here, we investigated the change of microbial necromass and plant-derived components in Moso bamboo forests with different unmanaged chronosequences (i.e., intensively managed currently or unmanaged for 2–5, 7–10, or 11–14 years), using biomarker. We observed that plant-derived C was significantly higher in unmanaged than in intensively managed forests and that the highest content was found in the forests left unmanaged for 7–10 years (3.69 g kg−1). No significant differences in microbial-derived C content were observed between Moso bamboo forests under intensive management and those left unmanaged for 2–5 years. However, compared with intensive management, left unmanaged for 7–10 and 11–14 years significantly increased microbial-derived C content. Overall, the quantitative importance of microbial-derived C as part of SOC was higher than that of plant-derived C (28.7–42.62 % vs 8.88–20.8 %, respectively). Moreover, we found that the major determinants of microbial- and plant-derived C were different. For microbial-derived C accumulation, plant biomass, total nitrogen, total phosphorus, and soluble organic C were the dominant factors, and for plant-derived C accumulation, soil cation exchange capacity was the dominant factor. These findings provide new information about the changes in SOC accumulation in Moso bamboo forests left unmanaged and highlight the different accumulation mechanisms of plant- and microbial-derived C.