Decades of reforestation significantly change microbial necromass, glomalin, and their contributions to soil organic carbon

Microbial necromass carbon (MNC) and glomalin-related soil protein (GRSP) are stable microbe-derived sources of carbon (C) in soils. MNC constitutes a considerable portion of soil organic carbon (SOC). GRSP is beneficial for soil aggregation, quality improvement, and C storage. However, the impact of land use transitions from crop-lands to forests on MNC, GRSP, and their contributions to SOC are not fully understood. To illuminate these unclear dynamics, soil was collected at depths of 0-10 cm from 30 pairs of adjacent corn fields and woodlands in southwest China. These woodlands, mainly consisting of fir, pine, and rubber, were converted from croplands approximately two decades ago. Soil properties, SOC, MNC, and GRSP content were determined. We found that SOC content increased significantly by 23.24% following reforestation. Additionally, the MNC and total GRSP contents were 46.01% and 20.48% higher, respectively, in woodland soils than in adjacent cropland soils. The contribution of MNC to the SOC pools also significantly increased and their quantities were proportional to the increasing contribution of GRSP to SOC. In woodlands, soil NH4+-N content is the major factor regulating the accumulation of MNC. For cropland systems, the easily extractable GRSP showed a strong positive correlation with MNC accumulation. Overall, our findings show that reforestation from croplands is conducive to soil C sequestration. The positive relationship between the contributions of GRSP and MNC to SOC provides valuable information in terms of enhancing our understanding of mechanisms underlying the maintenance of soil C stocks through microbe-derived C.