Retention characteristic of canopy litter delays carbon release in Cunninghamia lanceolata plantations: Evidence from an aerial decomposition experiment

Litter decomposition is a fundamental process that governs carbon cycling in forests. Marcescence (retention of dead branches and needles) in Cunninghamia lanceolata plantations represents a significant component of the dead carbon pool. However, the decomposition dynamics of canopy litter during the aerial retention stage remain largely unknown. Here, we quantified the biomass and vertical distribution of canopy litter along a chronosequence of C. lanceolata plantations and used the mesh bag method to measure the remaining litter dry mass and carbon release rate in the air and on the ground over 360 days. The biomass of canopy litter in young, middle-aged, and mature C. lanceolata plantations was 4369.30, 3637.09, and 3681.28 kg·ha⁻ 1 , respectively, with vertical distribution ranges of 0–4 m, 0–5 m, and 2–9 m. Across these three developmental stages, the mean decay constants for the aerial decomposition of canopy branch litter were 0.128, 0.100, and 0.102 year⁻ 1 , respectively, while those of canopy needle litter were 0.207, 0.160, and 0.153 year⁻ 1 . Compared with ground decomposition, aerial decomposition resulted in decay constants for canopy litter that were lower by 13.03–19.30%, 27.90–33.33%, and 17.07–29.72% in young, middle-aged, and mature stands, respectively. Correspondingly, the annual carbon release mass from aerial decomposition was reduced by 58.35, 94.79, and 59.28 kg·ha⁻¹ , respectively. Aerial decomposition of canopy litter is thus an important ecological process in C. lanceolata plantations, which favors carbon reduction. This study provides a scientific basis for precisely evaluating carbon cycling and formulating carbon-oriented management strategies for C. lanceolata plantations.