Abstract: Litter decomposition is a crucial biogeochemical process in wetland ecosystems, which significantly impacts soil fertility and carbon cycling. In this study, we conducted a 450-day in-situ field experiment in the Nanji Wetland of Poyang Lake using the litterbag method, to investigate the decomposition rates of aboveground litter and roots, as well as the dynamic changes in carbon (C), nitrogen (N), and phosphorus (P) release of three dominant plant species (Carex cinerascens, Triarrhena lutarioriparia, and Phragmites australis). The results showed that root decomposition rate (k) of all the three species was significantly faster than that of aboveground litter, and exhibited rapid decomposition during the early stage (0-90 d), with rates all exceeding 0.0017 d^-1. Throughout the decomposition process, the mean concentrations of TC and TN in aboveground litter and roots of the three species were significantly higher in the early stage compared to mid-late stages, exhibiting a net release pattern of C and N. Further, during decomposition, TP concentration of C. cinerascens showed significantly higher in aboveground litter than in roots, with C. cinerascens exhibiting significantly greater TP concentration compared to T. lutarioriparia and P. australis, while there were no significant differences in TC and TN concentrations among the three species. The aboveground litter and root decomposition rates (k) of the three species showed significant positive correlations with TC and TN concentrations, C∶P ratios, N∶P ratios. Root decomposition rates (k) were significantly negatively correlated with TP concentrations and C∶N ratios. The decomposition rate of roots exceeded that of aboveground litter, and TP concentration in C. cinerascens litter exhibited the most pronounced sensitivity to seasonal environmental variations. These findings provide critical empirical support for elucidating the decomposition patterns of dominant plant litter (aboveground and belowground) and carbon dynamics in seasonal lake wetlands.

Key words: Poyang Lake wetland, litter decomposition, nutrient release, stoichiometric ratio