The Patterns of Microbial-Derived Carbon and Particulate Organic Carbon in Subtropical Forest Ecosystem: Implications for Carbon Sequestration and Stability

Different forest ecosystems affect the acquisition and loss of SOC by changing the niche differentiation of above-ground and under-ground, resulting in changes in the utilization efficiency of water and nutrient elements. The impact of different types of forests on carbon storage in forest soils has received significant attention in recent decades, as these ecosystems are critical for mitigating the effects of global climate change. There are significant differences in environmental factors among different types of forests, such as carbon source type, topographic characteristics, soil texture, microbial community status, climate and hydrological conditions. At present, the research on the effects of environmental factors such as climate, hydrological conditions or soil quality on SOC has been well carried out. Nevertheless, the distribution pattern of microbial carbon and particulate organic carbon in subtropical forest ecosystems and their contribution to SOC still need much of scientific research. Forest types have a significant impact on the content and distribution characteristics of MNC and particulate organic carbon fractions, but there is heterogeneity in different forests. Importantly, the random forest analysis showed that MNC and MAOC were the main factors affecting SOC compared with other variables, which indicated MNC and MAOC have higher relative importance to SOC (p < 0.05). Specifically, our research found that the total MNC and BNC content in natural forests and broad-leaved forests were significantly higher than that in coniferous forests (p < 0.05), while the FNC content and FNC/BNC in coniferous forests were significantly higher than that in the other two forests (p < 0.05). In addition, the MAOC content of natural forests was higher than others, which indicated the stability of natural forest is higher than other forests. However, CPOC, FPOC content, and POC/MAOC in coniferous forests were significantly higher than in broad-leaf forests and natural forests. Biotic and abiotic factors profoundly affect the dynamic changes in SOC accumulation and stability. Different environmental factors lead to more MNC and MAOC in forest types with faster decomposition rates. These findings have instructive implications for understanding the contributions of different forest types on SOC stability and accumulation mechanisms in forest soils.