湿地是全球重要的碳库和CH4排放源，随着大气CO2浓度升高，滨海湿地碳累积、向海洋输出碳和CH4排放将如何变化，作用机制是什么，目前尚无定论。本项目以黄河三角洲湿地为研究基地，利用涡度相关系统，监测盐蒿和入侵植物互花米草湿地与大气间CO2和CH4净交换，明确植物入侵对湿地生产力和CH4排放的影响；在潮沟入海口建立潮水流量等测定系统，研究潮水溶解性有机碳（DOC）含量和组成的季节性变化规律，明确不同植被湿地向海洋输出DOC的强度和特征；建立开顶箱CO2熏气系统，利用静态箱法等，揭示湿地生产力、CH4排放和DOC含量/组成对CO2浓度升高的响应规律和强度；运用酶学、DNA-SIP等技术，研究湿地DOC产生关联微生物和酶及甲烷产生与氧化功能菌丰度/群落结构，阐明DOC产生的微生物和酶学机制，解析CH4排放对大气CO2倍增响应的微生物机制，为评估未来大气CO2升高对湿地碳循环影响效应提供科学依据。

Wetland is an important soil carbon pool and a source of CH4 emission in the world. With the increase of atmospheric CO2 concentration, how changes in soil organic carbon accumulation and CH4 emissions in coastal wetlands and transportation of dissolved organic carbon (DOC) into the ocean are not clear. The objectives of this study are to (1) quantity the productivity of different plant wetlands and effect extent of elevated CO2; (2) evaluate the magnitude of DOC output of different plant growing coastal wetland to the ocean and the response of DOC output to elevated CO2; (3) understand how elevated CO2 affects CH4 emission in coastal wetlands by measuring the key functional methanogens and methanotrophs, and evaluate the influence of elevated CO2 on DOC content/characteristics by measuring C-transforming microbes and enzymes. We selected coast wetlands in the Yellow River Delta as the present study site. The net exchange of CO2 and CH4 between C3 indigenous plant Suaeda salsa (or C4 invasive plant Spartina alterniflora) wetland ecosystem and the atmosphere will be measured using the vorticity correlation system to quantify the impact of plant invasion on wetland ecosystem productivity and CH4 emissions. We will also set up the measurement system for seawater flow and DOC in seawater in tidal channels such as estuaries, and the seasonal variation of DOC content and composition in tidal channel water will be monitored to quantify the magnitude and characteristics of DOC output from different plant growing wetlands to the ocean. An in situ open-top chamber of CO2 fumigation system will be established, and the responses of wetland productivity, CH4 emissions and DOC content/composition in soil porewater to the elevated CO2 will be studied. By collecting porewater in wetlands under ambient and elevated CO2, the response of DOC content and characteristics to elevated CO2 will be evaluated and key enzymes or microbes relative to DOC production will be identified. By collecting soil samples and analyzing functional methanogens and methanotrophs using DNA-SIP technique, key functional methanogens and methanotrophs and shifts in their community structure under elevated CO2 will be identified. Thus, this study could provide the evidences and prediction model for the potential impact of future atmospheric CO2 increase on carbon cycle in coastal wetlands.