Abstract: Coastal wetlands are fragile and ecologically sensitive areas that are facing severe environmental challenges, such as sea level rise. The invasion of seawater has led to an increase in soil salinity, bringing a series of negative effects such as soil nutrient imbalance and reduced productivity. To investigate the effects of soil salinity on soil organic carbon (SOC) and available phosphorus (AP) content, soil samples were collected from typical coastal wetlands in Tianjin. The contents of SOC, AP, different P forms, soil salinity, pH, particle size, and alkaline phosphatase activity were measured. The results showed that SOC content varied from 1.88 to 8.51 g·kg^-1 and the AP content varied from 10.50 to 56.07 mg·kg^-1, including H₂O extracted and NaHCO₃ extracted P. Ca-bound P from HCl extraction dominated the inorganic P. With the increases of salinity, SOC and AP contents showed a trend of firstly increasing and then decreasing. SOC content was significantly positively correlated with soil total nitrogen content, alkaline phosphatase activity and NaOH-P content, and significantly negatively correlated with soil sand fraction. AP content was significantly positively correlated with total P, NaHCO₃-P, NaOH-P, and H₂O-P contents, and negatively correlated with soil sand fraction. This study revealed the characteristics and influencing factors of salinity response of SOC and AP contents in coastal wetlands, which provides reference for nutrient management of coastal wetlands in the context of global change.

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