滨海湿地生态系统具备较高的固碳速率和持续的碳固存能力，是地球上最重要的碳库之一。非生长季土壤CO₂排放量是年际碳排放的重要组成，相较于生长季的大量排放，滨海湿地非生长季CO₂排放容易被忽视。明确滨海湿地非生长季CO₂排放特征是完善蓝碳生态系统碳循环过程中的重要一环，对于滨海湿地蓝碳生态系统碳库稳定性可起到重要的指导作用。本研究以黄河三角洲湿地土壤有机碳矿化过程为研究核心，基于野外原位监测与室内培养实验，开展了冬季不同水盐条件下滨海湿地CO₂排放规律研究，揭示了冻融循环情景下滨海湿地CO₂排放对水盐交互作用的响应机理；运用¹³C同位素标记手段，剖析了冻融循环条件下盐度对土壤有机碳矿化速率的影响，明晰了土壤激发效应强度的影响机制；通过CoupModel模型预测了滨海湿地非生长季土壤水热特征和CO₂排放通量，提出了滨海湿地冻融循环情景模拟预测方法。本研究的主要结论如下：

（1）温度是影响非生长季黄河三角洲湿地土壤CO₂排放的重要限制因素，土壤冻结只发生于表层土壤（0-10 cm）。土壤CO₂排放趋势表现为先下降后上升，其中低潮滩与中潮滩12月至1月CO₂排放通量均显著下降，并由CO₂的源变为汇，而中潮滩和淡水区在1月仍表现为CO₂的源；2月份低潮滩与中潮滩CO₂排放相比1月均有显著提升。冻融循环显著改变了土壤粒径占比，其中低潮滩沙粒占比由12月至1月显著降低了9.98%，中潮滩粉粒由12月至1月显著下降了23.63%；土壤粒径占比显著影响土壤相关碳氮指标，颗粒直径越小的土壤类型其相关碳氮指标含量越高。

（2）滨海湿地潮间带土壤气泡产生是非生长季CO₂排放的重要形式，盐度与水分是土壤盐结皮形成的最重要因素。气泡中的CO₂浓度可达1724.45±401.96 ppm，随着气泡体积的增加，气泡碳输出含量均有所增加，且较大体积的土壤气泡相比体积较小的气泡会释放更多的CO₂。冬季土壤气泡表层细菌群落中拟杆菌门 (Bacteroidota) (22.91%) 相对丰度最高，与下层和夏季表层土壤优势细菌群落为变形菌门 (Proteobacteria) 有所差异；相较于冬季，夏季气泡表层土壤微生物具有更加复杂的相互关系，模块化程度更高。

（3）冻融循环条件下外源碳添加均导致不同盐度土壤产生正激发效应，高盐与中盐土壤有机碳矿化速率最高值均出现在培养的第3天，且高盐土壤激发效应强度高于低盐和中盐。冻融条件下土壤CO₂排放量几乎全部来自于外源碳添加（超过98%），外源碳的添加导致高盐土壤碳矿化速率显著高于中盐和低盐，同时增加了高盐土壤有机碳累积矿化量。中盐土壤DOC含量由1次循环至6次循环显著提升了31.79%，随后呈逐渐下降趋势，低盐土壤在6次冻融循环时刻表现为DOC最高值，高盐土壤DOC含量由1次循环至24次循环显著降低了10.21%。冻融循环导致了土壤较小粒径占比增加，随着冻融次数的增加，土壤粘粒占比均有显著的提升。

（4）基于CoupModel模型对非生长季黄河三角洲土壤温度、含水率与CO₂排放通量进行模拟发现，随着土壤深度的加深，土壤温度模型拟合精度随之增加，20-30 cm 深度土壤温度模拟RMSE值（0.88）更接近于0，表明模拟值与实际值更为接近。土壤含水率模拟精度分析发现 0-10 cm与20-30 cm深度的土壤含水率RMSE值更接近于0，其模拟值与实际值更为接近；模型预测深层土壤含水率大小结果为70-100 cm >50-70 cm > 30-50 cm。黄河三角洲湿地土壤CO₂排放通量随着冻融时间的增加逐渐增大，主要表现在0-10 cm土壤，其中排放通量最大值出现在冻融后期；土壤30 cm以上深度CO₂排放通量呈现出昼夜波动特征，与土壤温度受冻融影响的昼夜变化特性一致。

Coastal wetland ecosystem has high carbon sequestration rate and sustainable carbon sequestration capacity, which is one of the most important carbon pools on the earth. Soil CO₂ emissions during non growing season are important components of interannual carbon emissions. Compared with the large amount of carbon emissions in the growing season, carbon emissions of coastal wetlands are easy to be ignored in the non growing season. Clarifying CO₂ emission characteristics of coastal wetlands in the non growing season is an important part of improving the carbon cycle of the blue carbon ecosystem, which can play a considerable guiding role in the stability of the carbon pool of the coastal wetland. Taking the mineralization process of soil organic carbon in the Yellow River Delta as the research core, based on field in-situ monitoring and indoor culture experiments, CO₂ emission characteristics of coastal wetlands under different water and salt conditions in winter were carried out, and the response mechanism of CO₂ emission of coastal wetlands to the interaction of water and salt under freeze-thaw cycle was revealed; by ¹³C exogenous carbon labeling method, the effect of salinity on the mineralization rate of soil organic carbon under freeze-thaw cycle was analyzed, and the mechanism of soil organic carbon excitation effect was clarified; through the CoupModel, the soil hydrothermal characteristics and CO₂ emission flux in non growing seasons of coastal wetlands were predicted, and the scenario simulation prediction method of freeze-thaw cycle in coastal wetlands was proposed. The main conclusions of this study were as follows:

(1) Temperature was an important limiting factor affecting soil CO₂ emissions in non growing seasons, and soil freezing only occured in the surface soil (0-10 cm). The trends of soil CO₂ emission were first decreased and then increased. The CO₂ emission flux of low tidal flat and middle tidal flat decreased significantly from December to January, and changed from CO₂ source to sink, while the middle tidal flat and freshwater area still showed CO₂ source in January; CO₂ emissions from low tidal flat and middle tidal flat increased significantly in February compared with January. The freeze-thaw cycle significantly changed the proportion of soil particle size, in which the proportion of sand particles in low tidal flat decreased significantly by 9.98% from December to January, and the proportion of silt particles in middle tidal flat decreased significantly by 23.63% from December to January; the proportion of soil particle size significantly affects the soil related carbon and nitrogen indicators, that the smaller particle diameter promoted the higher the content of soil carbon and nitrogen indicators.

(2) Soil gas bubbles in the intertidal zone of coastal wetlands were important forms of CO₂ emissions in non growing seasons, salinity and water conditions were the most important factors for the salt crust formation. The CO₂ concentration in the gas bubbles could reach 1724.45±401.96 ppm. With the increase of bubble volume, the carbon output contents would increased, indicating that larger gas bubbles will release more CO₂ than smaller bubbles. Bacteroidota (22.91%) was the main bacterial community with the highest relative abundance in the surface of gas bubbles in winter, which was different from the dominant bacterial community (Proteobacteria) in the lower layer and surface soil in summer; compared with winter, the soil microorganisms of the surface in summer had more complex relationships and higher modularity.

(3) Under the condition of freeze-thaw cycle, the addition of exogenous carbon resulted in positive excitation effect in the soils with different salinities. The highest mineralization rate of organic carbon in high salinity and medium salinity soils occurred on the third day of the incubation experiment, and the excitation effect intensity of high salinity soils was higher than low salt and medium salinity soils. Almost all CO₂ emissions of soil were from the addition of exogenous carbon under freeze-thaw conditions (more than 98%), which led to the carbon mineralization rate of high salinity soil was significantly higher than medium and low salinity soil, also increased the cumulative mineralization of organic carbon in high salinity soil. DOC contents in medium salinity soil increased significantly by 31.79% from one cycle to six cycles, and then gradually decreased; DOC contents in low salinity soil showed the highest value during six freeze-thaw cycles, while the contents of high salinity soil decreased significantly by 10.21% from one cycle to 24 cycles. The freeze-thaw cycle led to an increase in the proportion of soil particles with smaller diameters. With the increase of freezing and thawing times, the proportion of soil clay particles increased significantly.

(4) Based on the CoupModel, soil temperature, moisture content and CO₂ emission flux of the Yellow River Delta in non growing seasons were simulated and predicted. With the increase of soil depth, the RMSE value of the soil temperature simulation at the depth of 20-30 cm was closer to 0, indicating the simulated value is closer to the actual value. The simulation accuracy analysis of soil moisture content showed that the RMSE values at the depth of 0-10 cm and 20-30 cm were closer to 0, indicating the simulated values were closer to the actual value. The model predicted that the soil moisture contents at deep layer showed 70-100 cm >50-70 cm > 30-50 cm. The CO₂ emission flux mainly in 0-10 cm soil of the Yellow River Delta gradually increased with the increase of freezing and thawing time, of which the maximum emission flux occured in the late freezing and thawing period. The CO₂ emission flux from deep soil (more than 30 cm) showed the characteristics of diurnal fluctuation, which was consistent with the diurnal variation of soil temperature affected by freezing and thawing.