The patterns of forest soil particulate and mineral associated organic carbon characteristics with latitude and soil depth across eastern China

Forest ecosystems function as the largest carbon (C) sink in terrestrial ecosystems, and nearly half of the C in forest ecosystems is stored in forest soils. However, the patterns of two main fractions of soil organic C, particulate organic C (POC) and mineral-associated organic C (MAOC), across various types of forest ecosystems remain unclear. In this study, soil samples were collected from depths of 0-100 cm at eight sites located between 18 degrees and 48 degrees north latitude in eastern China. The soil samples were then separated into particulate organic matter (POM) and mineral-associated organic matter (MAOM) based on particle size to analyze the distribution of C within each fraction. The results showed that the C stored as POC increased with latitude and decreased with soil depth. Specifically, 28.1%, 38.5% and 55.6% of C was stored as POC in the topsoil (0-30 cm) of tropical, subtropical and temperate forests, respectively, while 24.0%, 24.3% and 38.9% of C was stored as POC in the subsoil (30-100 cm) of the corresponding forests, respectively. MAOC experienced a higher degree of microbial processing (indicated by differences in delta 13C, delta 15N and C:N between POM and MAOM) than POC, with a more pronounced difference in microbial processing between MAOC and POC at lower latitudes than at higher latitudes. These findings contribute to a comprehensive understanding of the characteristics of forest SOC and offer potential strategies for enhancing forest C sequestration.