Abstract: As important components of soil organic carbon (SOC), soil amino sugars and lignin phenols serve as reliable biomarkers for microbial- and plant-derived C, and their relative contents provide critical insights into the SOC composition and stability. However, the dynamic changes of soil amino sugars and lignin phenols with restoration time in the widely planted subtropical Castanopsis hystrix plantations remain unclear, which limits the development of scientific management strategies. Here, we analyzed soil amino sugars, lignin phenols and the related biotic and abiotic factors at two soil depths (0–10 cm and 20–30 cm) across various stand age of Castanopsis hystrix plantations in southern China. The results showed a divergent accumulation of soil amino sugars and lignin phenols with stand age, in which the ratio of soil amino sugars to SOC exhibited a unimodal pattern with stand age in the topsoil (0–10 cm), while the ratio of soil lignin phenols to SOC decreased with stand age in both soil depths. Consequently, the ratio of soil amino sugars to lignin phenols increased with stand age, particularly in the subsoil (20–30 cm). Further analysis indicated that the divergent accumulation of soil amino sugars and lignin phenols with stand age was mainly related to changes in the litter biomass and quality, while the divergence with soil depth was primarily driven by microbial residue formation efficiency. These findings demonstrate the SOC composition shift from plant-derived C to microbial-derived C during plantation restoration, offering important implications for forest management practices and nature-based climate solutions.

Key words: microbial-derived C, plant-derived C, restoration, forest ecosystem, forest soil