Objective The content of recalcitrant compounds in litter constitutes a crucial intrinsic factor influencing decomposition rates, serving as a pivotal component in nutrient cycling within forest ecosystems. Forest gaps mediate the degradation process of refractory substances by buffering microclimatic disparities between canopy interiors and exteriors. However, comprehensive understanding remains limited regarding how litter-derived recalcitrant compounds respond to heterogeneous gap environments.

Method In the end of May 2018, gap and non-gap plots were established in the Castanopsis kawakamii natural forest reserve, Sanming City, Fujian Province of eastern China. Focusing on leaf and branch litter of Castanopsis kawakamii, this study investigated how gap size regulates the decomposition of recalcitrant substances (tannins and total phenols), thereby identifying key drivers governing their decomposition dynamics.

Result Gap size significantly affected the decomposition of recalcitrant litter components (p < 0.001). The decomposition of tannins in leaf litter in large forest gaps was the fastest, while in non forest gaps, it was the slowest; the tannin decomposition of branch litter in small forest gaps was the fastest, while in medium forest gaps, it was the slowest; the total phenolic decomposition of leaf litter in large forest gaps was the fastest, while in small forest gaps, it was the slowest; the total phenolic decomposition of branch litter in the central forest gaps was the fastest, while it was the slowest in non forest gaps.

Conclusion Forest gaps significantly influence the decomposition of litter tannins and total phenolics by modifying understory microenvironmental factors such as canopy openness and soil temperature. These findings advance our understanding of soil ecological balance and material cycling in forest ecosystems.