Abstract: Soil respiration plays a critical role in the CO₂ emissions of terrestrial ecosystems. It is of great significance to identify the dynamics of CO₂ and its controlling factors for global change research. Nevertheless, continuous in-situ observations of soil respiration in wetlands are relatively rare. In this study, we utilized CO₂ flux sensor and soil temperature and moisture sensors to continuously monitor soil respiration in the Qilihai wetland, located in Tianjin, the Bohai Rim. Our objective was to investigate the diurnal and seasonal variations of CO₂ flux, hydrothermal factors in wetland soil, and the response of CO₂ flux to soil hydrothermal factors during the growing season (May 1 to September 30, 2022). The results showed that soil CO₂ flux exhibited a first increasing and then decreasing trend during the growing season, with a mean value of 6.68±2.55 μmol·m^-2·s^-1. Temperature was positively correlated with soil CO₂ flux, which explained 75.7% of the variation in soil respiration during the study period. Moreover, wetland soil demonstrated a strong temperature sensitivity of soil respiration, with a Q₁₀ value of 3.21. On a diurnal scale, CO₂ flux displayed a unimodal variation, with a lag effect to soil temperature and a counterclockwise characteristic overall. Additionally, soil respiration exhibited a weak negative correlation with soil water content. With the limitations of initial soil moisture, CO₂ flux reached a transient peak at the beginning of rainfall event, followed by a significant reduction in CO₂ emissions during the rainfall, and then a rapid increase in CO₂ flux at the end of the short-term rainfall. Overall, our results illustrated that soil temperature was the primary controlling factor for soil respiration during the growing season, and soil respiration was also influenced by soil water content during rainfall events. Thus, future warming and rainfall frequency associated with climate change could lead to significant changes in soil carbon fluxes in wetland ecosystems.

Key words: wetland, soil respiration, soil temperature, Q₁₀, hysteresis, rainfall event