Abstract: To investigate vegetation structure and carbon sink function of blue carbon ecosystems at the Mulan River estuary in Putian City, we conducted field surveys, sediment sampling, and laboratory analyses on mangrove and salt marsh communities that had been restored for five years. Combined with vegetation allometric growth equations and carbon density estimation methods, carbon storage of different communities was quantitatively analyzed. The results showed that the total carbon stocks of mangroves and salt marshes reached 8158.57 and 5289.62 t C, respectively. Among the three mangrove species investigated, Avicennia marina exhibited the highest carbon density (121.03 t C·hm^-2), followed by Kandelia obovata (100.87 t C·hm^-2), while Aegiceras corniculatum was the lowest (98.07 t C·hm^-2). In the salt marsh plant communities, carbon density was 99.46 t C·hm^-2 for Phragmites australis and 94.03 t C·hm^-2 for Suaeda community. In terms of carbon pool composition, both mangrove and salt marsh communities were dominated by sediment carbon pools, with carbon density of 82.54-97.23 and 93.10-94.32 t C·hm^-2, respectively, which were significantly higher than those of vegetation and litter carbon pools. Overall, the carbon density of the restored mangroves was lower than the national average and the level of natural mangroves, indicating that the communities were still at the early stages of restoration. Compared with other coastal wetlands in China, the sediment carbon density of salt marshes in the study area was at a moderate level, while vegetation carbon density was relatively low. These findings provide a scientific reference for the ecological restoration practices in coastal wetlands and the assessment of regional carbon sequestration capacity.

Key words: mangrove, salt marsh, carbon density, carbon pool composition, sediment carbon pool