Fungal Necromass Contributes More to Soil Organic Carbon and More Sensitive to Land Use Intensity Than Bacterial Necromass

Increasing evidence shows that microbial necromass carbon is the primary constituent of soil stable carbon, yet the dynamics under different land use intensity (LUI) in arable soils are unknown. Here, we evaluated the dynamics of microbial necromass carbon through biomarker amino sugars at topsoil (0-15 cm) and subsoil (15-30 cm) across different LUI. The LUI was calculated by integrating the application amount of nitrogen fertilizer and the planted number of crops in different cropping systems including cotton-wheat, grape-wheat, vegetable-wheat and watermelon-maize-wheat in North China Plain. We found that the fungal necromass C contributed more to SOC compared to bacteria at both soil depths. Total microbial necromass C showed no correlation with LUI. However, the contribution of fungal necromass-C to SOC was significantly negatively correlated with LUI at topsoil, which was mainly driven by C concentration in non-HCl soluble intra-microaggregate silt and clay. The bacterial necromass-C to SOC was significantly positively correlated with LUI at subsoil, which was mainly driven by soil microbial biomass C. This indicates that the microbial-derived organic C for maintaining and stabilizing soil C stock is important and the proper reduction of land use intensity may benefit for enhancing and stabilizing microbially-derived SOC in arable soils.