河口湿地植被对甲烷和氧化亚氮产生与排放的影响及其控制机制

Researches demonstrated that wetland plant is one of the key factors affecting and controlling the methane (CH4) and nitrous oxide (N2O) emission in estuary wetlands. But so far, there are many unknown details of the mechanism and biogeochemical processes. Yangtze estuary is located in the typical subtropical monsoon area, and growth rhythm of wetland plant and environmental factors have a clearly seasonal and spatial variation. A three years long-term investigation and sampling will be taken on the three kinds of the wetland plant in this area, Phragmites australis, Scirpus mariqueter and Spartina alterniflora. By using the transparent and opaque chamber technology and clipping treatment, we try to get the CH4 and N2O flux and its change during the photosynthesis and respiration period of wetland plant. Combined with the results of inner structure change of plant through their life time research, Eh change at rhizosphere between the photosynthesis and respiration period, organic carbon input from exude at rhizosphere of plant and the change of microbe community, the CH4 and N2O transporting mechanism in wetland plant and the effect mechanism of plant on CH4 and N2O production and consumption will be discussed. By integrating the correlation analyzing between the fluxes and the environmental factors, the effect and control mechanism of estuarine wetland plant on methane and nitrous oxide emission in subtropical monsoon area will be clarified. This research will enrich and develop the scope and depth of the estuarine wetland carbon and nitrogen biogeochemical cycling theory in China.

植被是影响和控制河口湿地甲烷（CH4）和氧化亚氮（N2O）排放过程的关键因子，然而其具体的影响机理和生物地球化学过程尚需深入研究和探明。长江口位于典型的亚热带季风气候区，河口湿地植被生长与环境因子季节和空间变化显著。选取该区域三种类型植被群落（芦苇、海三棱藨草、互花米草）为研究对象，计划通过三个年度的长期野外观测，使用黑白箱对照和剪切处理，获得河口湿地植被光合和呼吸作用下CH4和N2O排放通量的变化特征，结合植被生命周期中植被体内部结构的变化、光合与呼吸作用时根际沉积物氧化还原电位变化、植被根际分泌物输入有机碳特征和根际微生物群落变化，探讨湿地植被对CH4和N2O的传输机制及其对沉积物中CH4和N2O产生和消耗的控制过程。结合其它环境因子的相关分析，阐明亚热带季风区河口湿地植被对湿地-大气界面CH4和N2O排放的影响和控制机制，丰富和发展我国河口滨岸湿地碳氮生物地球化学循环理论。

为探究湿地植被对温室气体排放通量的影响及其固碳输入对沉积物中温室气体产生和排放的贡献，以及全球变化导致河口环境因子改变对湿地温室气体排放的影响，本项目通过野外观测、实验室模拟和长期培养等方法，对不同植被类型潮滩湿地温室气体排放过程和变化规律进行了研究。结果表明，潮滩湿地植被的光合作用和蒸腾作用对温室气体的产生和排放影响显著。芦苇合成的有机质能有效刺激甲烷（CH4）气体的产生，芦苇吸收的CO2量越多，CH4的排放通量也就越大。除此之外，芦苇茎秆是植株根部产生气体向上运输的重要通道，剪切芦苇地上部分会使CH4的排放通量提升86.03%。封口处理会使CH4通量比剪切条件下减少72.9%。温度、盐度和淹水条件对湿地植被区温室气体排放有显著影响。温度升高显著提升了CH4排放通量，但是CO2的吸收通量在芦苇群落中则会因为温度的增加被明显的削弱；水位从沉积物表面提升3cm会使芦苇群落的CH4排放通量增加2.87倍，而互花米草对水位的变化更为敏感，CH4通量在高水位条件下会比低水位条件提高7.49倍；芦苇群落的生物量在盐度为5‰下达到最高后显著减少，互花米草有更好的盐度适应能力，在生物量的变化上没有芦苇显著，而生物量的变化则会显著影响两种植物群落温室气体排放通量，低盐度条件下芦苇群落的温室气体通量显著大于高盐度条件，但是盐度的影响在互花米草群落的影响不够显著。培养温度越高，单位质量生物有机碳输入的CH4转化率也越高。芦苇、互花米草和海三菱藨草生物碳CH4的转化率，在5℃培养下，分别为0.0~0.09%、0.0%和0.0~0.50%；在20℃培养下，分别为0.02~6.14%、0.35%~3.64%和0.01~8.57%；在35℃培养下，分别为1.12~7.47%、0.58%~6.84%和0.04~9.79%。随着培养盐度的增加，单位质量植被有机碳CH4转化率随之减少。芦苇、互花米草和海三菱藨草生物碳CH4的转化率，在0‰盐度培养下，分别为0.30~4.46%、0.20%~4.67%和0.01~8.71%；在10‰盐度培养下，分别为0.21~4.30%、0.34%~4.70%和0.02~7.93%；在20‰盐度培养下，分别为0.17~3.51%、0.21%~4.06%和0.01~7.81%；在30‰盐度培养下，分别为0.13~2.97%、0.27%~3.68%和0.01~7.01%。