Divergent effects of cropland management practices and global change factors on microbial necromass across ecosystems: implications for soil organic carbon

Microbial necromass carbon (MNC) is a crucial contributor to Soil Organic Carbon (SOC), yet its responses to cropland management practices and global changes remain poorly understood. Here, a global meta-analysis was conducted to reveal general patterns of how MNC respond to these factors across major terrestrial ecosystems. Results showed that cropland management practices increased MNC by 6.5–29.4 %, with manure amendment having the largest effect (+29.4 %), followed by fertilization (+16.2 %), straw application (+13.1 %), no-tillage/reduced-tillage (NT/RT, +11.3 %), biochar amendment (+8.8 %), and cover crops (+6.5 %). In grasslands, warming increased MNC by 9.5 %, phosphorus (P) addition had negative effects on MNC, and nitrogen (N) addition had no effect. In forestlands, P addition increased MNC the most (+41.6 %), followed by NP (+33.4 %) and N addition (+11.3 %). Importantly, responses of MNC to management practices and global changes were influenced by climatic and edaphic factors. For example, fertilization and straw application increased necromass in humid and warm climates, while NT/RT and manure amendments were more effective in cooler climates or acidic soils. Fertilization, straw, and manure amendments led to greater MNC accumulation in soils with lower initial SOC levels. N addition had a more pronounced effect on necromass in humid forests, whereas P addition was more impactful in cooler climates. Furthermore, MNC was closely linked to SOC, highlighting the important role of microbial necromass in SOC sequestration. This study fills a key knowledge gap by synthesizing global evidence on how MNC responds to cropland management practices and global change factors, offering novel insights into optimizing land management strategies for soil carbon stabilization in future climate change.