Abstract: Coastal salt marshes are important blue carbon sink, which are sensitive to climate change. Assessing the carbon sink capacity of coastal salt marshes and their response to climate change is of great significance for China to achieving the carbon peaking and carbon neutrality goals. In this study, the DNDC (Denitrification-Decomposition) model was utilized to simulate the temporal and spatial variations of carbon sink in coastal salt marshes in different regions of Jiangsu Province, and to explore the responses of three typical salt marshes dominated by Phragmites australis, Suaeda salsa and Spartina alterniflora to long-term climate change. From 1981 to 2020, the total carbon sink of Jiangsu coastal salt marshes was 9.70 Tg C, and the total global warming potential (GWP) was -19.24 Tg CO₂-eq, with the largest total carbon sink and the negative effect on warming of Sheyang. Spatially, the carbon sink capacity and GWP in southern Jiangsu were greater than those in the north, and varied among the three types of salt marshes. The carbon sink capacity was in a descending order of Spartina alterniflora, Phragmites australis, and Suaeda salsa, while GWP followed an order of Phragmites australis < Spartina alterniflora < Suaeda salsa. In terms of interannual variation, net primary productivity (NPP) and GWP of the three salt marshes in various sites showed an increasing trend from 1981 to 2020. The carbon sink capacity varied greatly across different years, but the changing trend was not obvious on the whole. With the increase of temperature, NPP of Suaeda salsa and Spartina alterniflora increased, while that of Phragmites australis decreased. The changes in CH₄ and N₂O emissions were significantly greater than those of NPP. CH₄ and N₂O emissions increased significantly except for the different trends of N₂O emissions in Phragmites australis in different regions. Rainfall was positively correlated with NPP and CH₄ emissions in Phragmites australis and Spartina alterniflora, while Suaeda salsa showed an opposite pattern. Rainfall was positively correlated with N₂O emissions in three salt marshes.

Key words: salt marsh, coastal blue carbon, carbon dynamics, climate change, DNDC model