Abstract: Litter leaching is the initial stage of mangrove litter decomposition, and regulates the initial release of carbon and nutrients to adjacent waters. This study aimed to elucidate the regulatory mechanisms of litter chemical quality on the leaching process and the release patterns of carbon (C), nitrogen (N), and phosphorus (P). We conducted a laboratory experiment simulating tidal inundation with leaf litter of single-species and mixed-species of three mangrove species from Qi’ao Island, Zhuhai, including Sonneratia apetala, Kandelia obovata, and Acanthus ilicifolius. Over a 14 days leaching period, the dynamics of litter dry mass loss, C, N and P contents, and the concentrations of dissolved organic carbon (DOC), total dissolved nitrogen (TDN), and total phosphorus (TP) in the water were monitored. The results showed that: (1) Litter chemical quality (C, N and P contents, C/N ratio) governed the decomposition rate and elemental migration processes. High-quality litter (A. ilicifolius) decomposed the fastest, with a decomposition rate constant of k=0.2274 d^-1, significantly higher than that of K. obovata (0.1078 d^-1) and S. apetala (0.1124 d^-1). (2) Mixed litter decomposition exhibited significant non-additive effects. There was a synergistic effect in the K. obovata and A. ilicifolius mixture, with a decomposition rate (k=0.1277 d^-1) higher than that of the single-species treatments. In contrast, an antagonistic effect occurred in the S. apetala and A. ilicifolius mixture, with a lower decomposition rate (k=0.0975 d^-1). (3) There were significant differences in the migration pathways of C, N, and P among different litter combinations. The direct leaching loss of litter C as DOC was minimal, accounting for only 0.87% (S. apetala) to 3.31% (A. ilicifolius) of the initial C content. Nitrogen showed a higher potential for dissolved loss, with A. ilicifolius having the highest N leaching rate (12.2%) and the highest leachate N concentration (5.17 mg·L^-1). Phosphorus release was highly species-specific. S. apetala was the primary P source, with the highest final P leaching amount (0.53 mg·g^-1). The mixed treatments effectively suppressed P leaching. This study reveals the key regulatory mechanisms of litter quality and species interactions on C, N, and P release. It is recommended to enhance the monitoring of flux from different C loss pathways such as respiration and particulate C export. For mangrove ecological restoration, species configuration should be optimized according to different management objectives, and mixed planting is suggested to regulate material export.

Key words: mangrove, litter decomposition, Kandelia obovata, Sonneratia apetala, mixed-species effect