Patterns and controlling factors of soil microbial necromass carbon in global ecosystems

Microbial necromass is a critical source of soil organic carbon (SOC) in terrestrial ecosystems, and the quantity and quality of microbial necromass carbon (MNC) can influence long-term soil carbon sequestration. However, few studies have explored the distribution of soil MNC and its contribution to SOC along the soil profiles across different ecosystems globally. Here, we collected a global dataset (2, 411 samples from 216 papers) of soil MNC at a depth of 0-100 cm depth from wetlands, farmlands, grasslands, and forests. Our findings indicated that the average MNC at 0-30 cm was 2.7 g kg^-1 in wetlands, 7.1 g kg^-1 in farmlands, 17.2 g kg^-1 in grasslands, and 14.6 g kg^-1 in forests. The MNC content in deep soils (30-100 cm) was 70 % lower (p < 0.05) than in topsoil (0-30 cm), whereas the contribution of the MNC to the SOC in deep soils (50 %) was higher than in topsoil in forests (32 %). On average, the fungal necromass carbon(FNC) content (7.5 g kg^-1) was almost three times higher than the bacterial necromass carbon (BNC) content (2.8 g kg^-1) in the topsoill. The mean annual temperature played an important role in affecting the MNC by altering soil total nitrogen, soil texture and microbial biomass. These findings are important for understanding SOC formation mechanisms and the crucial role of microbial necromass in global ecosystems.