Impact of Downed Logs of Masson Pine (Pinus massoniana Lamb.) on Soil Microbial Community in a Climate Transitional Forest of Central China

Downed woody debris (DWD) can alter the chemical and biological properties of forest soils, and this process is affected by the degree of DWD decay. Our aim was to assess the effects of the entire decay process of DWD on the associated soil microbial communities. Here, we examined the differences in soil microbial community size and composition among five decay stages (DC Ⅰ–Ⅴ) of Masson pine (Pinus massoniana Lamb.) at two soil depths in a climate transitional forest and then linked these differences to soil chemical properties. The decay of DWD increased soil total PLFAs, and the complexity of soil microbial networks was highest in stage Ⅱ and then decreased with the decay stage. The relative abundance of fungi increased with the decay stage, while the relative abundance of gram-positive bacteria decreased with the decay stage. The microbial community composition at a soil depth of 0–10 cm was mainly driven by soil pH and organic C (SOC), and at a depth of 10–20 cm, soil pH was the primary determinant of microbial community composition. Our findings suggest that DWD decomposition reduces microbial physiological stress, promotes fungal growth, and stimulates microbial biomass, highlighting the positive impact of DWD on forest soils. Future research is needed to elucidate the universal effects of DWD decomposition on soil properties, especially focusing on the response of soil microbial processes to the decomposition time of DWD.