The effect of litter layer structure on soil organic carbon

Soil carbon pools constitute the world's largest terrestrial carbon storage system. The litter layer serves as a major source of soil organic carbon, and its components (such as broadleaf and coniferous leaves, as well as branches) are influenced by various environmental factors, with fallen leaves constituting the largest component of the litter layer. In this study, litter consisted primarily of dead branches and fallen leaves from chestnut forests, along with a small amount of surface vegetation. The microbial secondary metabolites and plant residues produced during their decomposition all contributed to the formation of soil organic carbon components—including total organic carbon (TOC), various forms of labile organic carbon (LOC), particulate organic carbon (POC), and mineral-associated organic carbon (MAOC). This study selected six chestnut forests of varying ages at the northeastern end of the Mount Tai range, collecting litter and soil samples to investigate how litter structure (biomass, leaf characteristics, decomposition rate, leaf moisture content) influences various soil organic carbon components. The aim is to enhance soil carbon sink functionality, support carbon neutrality goals, and lay the foundation for developing forest strategies to address climate change. Key findings include: (1) This study innovatively proposes that a leaf litter decomposition rate of 40%–50% represents the optimal carbon management range, simultaneously enhancing carbon sequestration efficiency and carbon stability. (2) There is a statistical correlation between litter structure and carbon composition: Leaf moisture content showed a significant positive correlation (P < 0.05) with micro-organic carbon (LOC-M), while aspect ratio showed no significant association with total organic carbon (TOC). (3) Soil moisture content independently explains approximately 48% of the variation in soil organic carbon content, making it an important environmental driver; soil aggregate condition accounts for 3% of the variation, which is also statistically significant. Both factors influence organic carbon accumulation through different biological and physicochemical pathways. Soil total organic carbon (TOC) is regulated by multiple factors.