Nutrient enrichment mitigates estuarine wetland CO2 emissions by reducing fungal stability and temperature sensitivity.

Increasing global nitrogen (N) and phosphorus (P) deposition significantly impacts carbon cycling in estuarine wetlands, yet the underlying microbial mechanisms remain unclear. This study selected the Phragmites australis wetland in the Shanyutan of the Min River Estuary as the research site. Four treatments were set up: control (CK), nitrogen (N) addition, phosphorus (P) addition, and combined nitrogen and phosphorus (NP) addition. Through a one-year in-situ experiment, we investigated how N, P, and combined NP additions regulate soil CO2 emissions, temperature sensitivity (Q10), and fungal community dynamics. The results showed that both nitrogen and phosphorus addition significantly increased soil electrical conductivity (EC) and water content (SWC) (p < 0.05). The N, P, and NP treatments all significantly reduced soil CO2 emissions by 25.83%, 20.46%, and 16.86% compared with the CK treatment, respectively (p < 0.05). Moreover, the N and NP treatments significantly decreased soil Q10 values (p < 0.05). N and P addition altered fungal community diversity and composition, accompanied by weakened network complexity, reduced modularity index, and decreased community stability. Correlation analysis indicated that CO2 emissions were significantly negatively correlated with EC and SWC, and significantly positively correlated with soil temperature (ST), bulk density (BD), and pH. Additionally, Dictyophora was significantly negatively correlated with CO2 emissions (p < 0.05). In summary, N and P addition weakened fungal community stability by changing soil physicochemical conditions, thereby slowing soil CO2 emissions. This study provides key scientific support for understanding the evolution of carbon cycling in estuarine wetlands under global N and P deposition, and provided results consistent with the microbial regulation theory of wetland carbon cycling.