Decomposition of mangrove leaf litter with different quality and its effects on the organic carbon components and sources in sediments

Litter decomposition is the process through which organic matter produced by mangroves is transferred to the sediment, with the stabilization of leaf litter carbon in sediment organic matter being crucial for mitigating climate change. This study analyzed the dynamics of carbon and nutrient release during litter decomposition through indoor ex situ controlled experiments and further traced the flow of litter carbon using carbon isotope labeling to quantify the proportion of litter carbon contributing to sediment carbon. Sediment organic carbon (SOC) content exhibited no significant change following short-term litter decomposition, indicating that respiration loss and water dissolution accompanied decomposition, and high-quality leaf litter input may balance sediment carbon loss. During short-term decomposition, 49.8 %–83.5 % of leaf litter carbon was decomposed, with 7.4 %–27.8 % of litter carbon fixed in sediment organic matter as mineral-associated organic carbon (MAOC), and 6.4 %–54.0 % as particulate organic carbon (POC), influenced by litter quality. High-quality leaf litter resulted in greater accumulation of both POC and MAOC, with higher MAOC transfer efficiency. Litter input promoted the production of ‘new carbon’ but did not significantly affect the total sediment MAOC, suggesting that new carbon formation may be accompanied by the loss of native carbon. The results provide important data on the key destinations of mangrove leaf litter carbon, highlight the importance of quantifying litter-derived carbon stabilization in mangrove sediments. Future research should prioritize quantifying lateral carbon exports (e.g., particulate and dissolved forms) and respiratory losses to fully understand mangrove blue carbon budgets.