[Distribution and Driving Factors of Contribution Rate and Stock of Global Microbial Necromass Carbon]

Microbial necromass carbon （MNC） is an important component of soil organic carbon （SOC） and plays a crucial role in the formation of stable SOC and the carbon cycle. However， due to the lack of global-scale observation data， the global distributions of the contribution rate of MNC to SOC and MNC stock remain unclear. Based on the combination of Meta-analysis and machine learning technology， the global spatial distribution characteristics and driving factors of the MNC contribution rate to SOC and MNC stock were evaluated， and the differences among six ecosystems and two soil layers were identified. The results showed that the contribution rate of MNC to SOC and its stock is higher in the deep layer （1-3 m） than in the shallow layer （0-1 m）. On average， the contribution rate of MNC in the shallow layer is 47%， and the rate in the deep layer is 60%. The average MNC stock in the shallow layer is 4.6 kg·m^-2， and that in the deep layer is 5.2 kg·m^-2. The total MNC stocks in the shallow layer and deep layer are 792 Pg and 895 Pg， respectively. The MNC stock is higher in the Northern Hemisphere than in the Southern Hemisphere because of the difference in land area. In addition， SOC and pH are the key drivers of the contribution rate of MNC， TN is the key driver of MNC stock， and MNC concentration has a direct and significant impact on both the contribution rate of MNC and its stock. The contribution rate of MNC to SOC and MNC stock show spatial heterogeneity in different ecosystems and different soil layers at the global scale， and their driving factors also differ. This study provides a theoretical basis for studying the SOC cycle and mitigating climate warming.