Dynamics in Soil Microbial Communities and Soil Carbon Fractions Across Early Developmental Stages of Young Poplar Plantations (0–15 Years)

Soil microbial communities play a central role in terrestrial biogeochemical cycling and ecosystem functioning, and their dynamics are closely linked to soil physicochemical properties, thereby contributing to ecosystem functional stability. However, the extent to which stand age regulates soil microbial community structure and soil physicochemical properties remains insufficiently understood. In this study, black poplar (Populus nigra) plantations located in the hilly region of Jiangsu Province, China, were selected as a chronosequence and classified into three stand age categories: young stands (HY), middle-aged stands (HH), and late-middle-aged stands (HN). Soil samples were systematically collected from the 0–15 cm layer. Soil physicochemical properties were measured, soil DNA was extracted, and high-throughput sequencing was performed to characterize age-related changes in microbial community structure. The results showed that mineral-associated total carbon reached its highest level in middle-aged stands, whereas dissolved organic carbon, microbial biomass carbon, and soil organic carbon (SOC) were highest in late-middle-aged stands. Co-occurrence network analysis further indicated that microbial interspecific associations were most complex during the middle-aged stage. Overall, stand age induced pronounced shifts in both soil carbon fractions and microbial community organization. These findings provide new insights into the coupling relationships among stand development, soil carbon dynamics, and microbial community succession in black poplar plantations.