Abstract: This study aimed to elucidate the dynamics of mangrove litter production and the return of carbon and nitrogen, and to assess the carbon sequestration potential of different mangrove communities. Using the litter collection frame method, we monitored the monthly dynamics of litter yield and the seasonal dynamics of carbon and nitrogen storage of each component (branches, leaves, flowers, and fruits) of the invasive species Sonneratia apetala and the native species Kandelia obovata on Qi’ao Island in 2022 and 2023. We examined the impact of species identity, forest age, and tidal level on monthly variations of litter production. We further estimated the aboveground carbon and nitrogen stocks based on litter yield and carbon and nitrogen contents. These efforts are of great significance for the ecological restoration and management of mangroves in coastal cities. The results showed that the monthly total litter production varied significantly across different months, forest ages, and tidal levels (P<0.001). The mean annual total production across the four plots was 1503.1 g·m^-2, with the ranking as follows: low tide 20-year-old S. apetala > high tide 20-year-old S. apetala > K. obovata > low tide 14-year-old S. apetala. Litterfall was predominantly composed of fallen leaves (45.6%), followed by fallen fruits (35.8%), and fallen flowers being the least abundant (1.5%). A peak in litter production was observed in summer and autumn, and the average monthly temperature was significantly positively correlated with the total litter production (P<0.01). The litter carbon and nitrogen contents, as well as their storage, exhibited significant variation across different components and seasons, with the carbon and nitrogen contents ranging from 400.9 to 477.2 mg·g^-1 and 8.9 to 26.3 mg·g^-1, respectively. Sonneratia apetala demonstrated superior annual carbon and nitrogen reserves of 1096.5 g·C·m^-2 and 66.14 g·N·m^-2, respectively, which were 1.9 and 3.7 times greater than those of Kandelia obovata, underscoring its higher capacity for carbon and nitrogen return. Litter production and its carbon and nitrogen storage are influenced by multiple factors, emphasizing the necessity taking into account the effects of seasons and components for the estimation of carbon and nitrogen budgets.

Key words: yield, seasonal dynamics, carbon stock, Kandelia obovata, Sonneratia apetala