Distribution, characteristics, and importance of particulate and mineral-associated organic carbon in China forest: a meta-analysis.

Background: Forest soil organic carbon (SOC) plays a critical role in the global carbon cycle, and increasing long-term forest carbon storage is essential for carbon sequestration. However, the distribution and drivers of mineral-associated (MAOC) and particulate organic carbon (POC) in forest soils at a continental scale remain poorly understood. Methods: Using 540 data points from 59 studies related to POC, MAOC, and total SOC in China's forests, we analyzed the distribution of POC and MAOC across forest type, soil depth and soil type, and further investigated their influencing factors. Results: MAOC accounted for more than 63% of total SOC in forest soils. Both POC and MAOC increase with forest age, with mixed forests showing faster growth compared to monoculture forests. The MAOC/SOC ratio decreases with forest age but increases with soil depth, demonstrating the dominance of MAOC in deeper soils. Importantly, MAOC content continuously increases with SOC, and exhibits no upper limit, suggesting the potential for persistent soil carbon accumulation. MAOC is closely associated to microbial biomass carbon, and POC is mainly related with plant litter biomass. Conclusion: MAOC and POC are influenced by different environmental factors and display distinct distribution patterns across forest types and soil depths. Thus, differentiating their respective responses to climate change is essential. The carbon sequestration potential of forests in China remains far from saturation.