Seasonal dynamics and vertical distribution of ecosystem-level carbon stocks in different vegetation types of the Minjiang estuary wetland

Coastal wetlands play a crucial role in the global carbon cycle and climate regulation by serving as significant reservoirs of ecosystem carbon stock. However, their carbon sequestration capacity is strongly influenced by vegetation types, as well as the seasonal dynamics and vertical distribution of soil organic carbon. In this study, four wetland ecosystem types in the Minjiang Estuary— Kandelia candel , Phragmites australis , Cyperus malaccensis , and the unvegetated Tidal flat (control)—were investigated to assess the characteristics of ecosystem carbon stocks. The results showed that total ecosystem carbon stock was highest in K. candel —dominated vegetation (161.00 t C ha -1 ), followed by C. malaccensis (155.29 t C ha -1 ), and P. australis (128.44 t C ha -1 ), while the Tidal flat exhibited the lowest carbon value (49.08 t C ha -1 ). Vegetated wetlands stored 2.6-3.3 times more carbon than unvegetated Tidal flats, underscoring vegetation’s key role in carbon accumulation. Across all sites, soils contained the vast majority (92.23%-95.05%) of ecosystem carbon, while vegetation accounted for only (4.94%-7.77%). Distinct seasonal patterns were observed that carbon stock in the K. candel ecosystem showed spring maxima and autumn minima, whereas the herbaceous wetlands ( P. australis and C. malaccensis ) peaked in autumn. In contrast, carbon stock in the Tidal flat peaked significantly during summer. Vertical distributions of soil organic carbon (SOC) stock exhibited distinct site-specific patterns. The K. candel wetlands exhibited SOC stock peak in the 20–40 cm soil layer across seasons, while the P. australis and C. malaccensis wetlands generally decreased SOC with depth increasing except for in autumn. In the Tidal flat, SOC stock increased with soil depth in spring and autumn but peaked at 20–40 cm in summer and winter. Correlations analysis indicated that soil moisture and temperature significantly promoted carbon accumulation, whereas high bulk density and low pH constrained carbon storage, particularly in K. candel and P. australis wetlands. These findings provide critical insights into the carbon stock dynamics and seasonal variability of different coastal vegetation types, offering a scientific basis for the conservation of coastal wetland ecosystems and the development of carbon enhancement strategies in China.