青藏高原高寒湿地温室气体排放对水位降低和氮沉降的响应

Wetland ecosystems play a critically important role in the greenhouse gases (GHGs) uptake and emission because their soil store large amounts of carbon and nitrogen. Although many studies have been conducted on GHGs flux from middle- and high-latitude wetlands around the world, studies in alpine wetland are still lack. The alpine wetlands in Qinghai-Tibetan Plateau are Asian water-tower and the Three Rivers source, but in recent decades, the wetlands are subjected to obvious drying, and the water table was lowered seriously. Water table drawdown will presumably lead to an increase in CO2 emission and a decrease in CH4 emission in wetland ecosystem, but its integrated greenhouse effect is not very clear. In our study, we extracted intact peat monolith from the Luanhaizi alpine wetland (altitude 3200 m) in Haibei, Qinghai province, and constructed a facility to manipulate water table (control, -20cm) and simulate N deposition (control, +30kg N ha-1yr-1), yielding a full-factorial experimental design. Additionally, an in situ long-term automated measurement of GHGs flux has also been conducted along a water table gradient since 2008. We quantified the diurnal, seasonal and inter-annual variability of GHGs fluxes and investigated the effect of water table lowering and N addition on GHGs emissions, which may provide important information for evaluating the role of wetland in GHGs emissions in the future.

湿地生态系统在二氧化碳、甲烷等温室气体（Greenhouse gases, GHGs）的吸收和排放中具有重要作用。国内外学者针对中高纬度地区湿地在全球变化下GHGs通量方面已经做了较多工作，但高寒湿地却是研究的薄弱环节。青藏高原高寒湿地是亚洲水塔，三江之源，近几十年来经历着明显的干化作用，水位下降明显。对于湿地生态系统，水位下降意味着二氧化碳排放的增加，甲烷排放的减少，但它们的综合温室效应如何仍不清楚。本研究以海拔3200m的青海海北乱海子高寒湿地为对象，利用原状土柱（0.6m×0.6m×0.6m），进行水位降低（对照，水位降低20cm）和模拟氮沉降(对照，增加30kg N ha-1yr-1)的交互实验，结合湿地沿水位梯度GHGs排放的长期监测，通过对GHGs通量日变化、季节变化和年际变化的测定，探讨水位降低和氮沉降对湿地GHGs排放的影响，为评估未来高寒湿地对GHGs的贡献提供理论依据。

近年来青藏高原经历着快速气候变化和日益增多的人为活动，导致了湿地水位的降低和氮沉降的增加，而这些变化可能极大地影响着高寒湿地甚至区域的温室气体排放。.本项目以青海海北乱海子湿地为对象，基于涡度相关系统和中宇宙（Mesocosm）实验平台，并结合过程机理生态系统模型（TEM）和宏基因组学方法（GeoChip 5.0），首次报道了青藏高原高寒湿地全年甲烷（CH4）排放动态及其控制因素，评估了青藏高原1979-2100年净二氧化碳（CO2）和CH4排放，探讨了全球变化背景下高寒湿地三种温室气体（GHG）排放的变化及其背后的分子生物学机制。..涡度相关法监测表明2012和2013年湿地年CH4排放量分别为26.4和33.8 g CH4 m-2，且非生长季排放贡献占全年的43.2-46.1%，表明非生长季高寒湿地CH4排放不容忽视；通径分析显示生长季CH4排放受土壤温度、水位和总初级生长力影响，而非生长季CH4排放主要受土壤温度控制。模型结果预测青藏高原在2030s之前对气候系统有增温效应，之后将转变为冷却效应。中宇宙实验发现，水位降低导致CH4排放降低57.4%，但对生态系统净CO2交换量和氧化亚氮（N2O）通量无显著影响；氮沉降增加了生态系统净CO2吸收（25.2%）和N2O排放，但对CH4排放没有显著影响；宏基因组学分析进一步表明，水位降低处理下，CH4产生潜势的降低而不是CH4氧化潜势的增加，是导致净CH4排放减少的原因。..本项目加深了对高寒湿地温室气体排放动态和大小的认识，为评估未来青藏高原高寒湿地和高原区域对全球温室效应的贡献提供了理论依据，且强调了微生物机制在调控生态系统尺度上温室气体对环境变化响应方面的重要性。项目发表论文9篇，其中SCI论文6篇，中文期刊3篇。还有1-2篇重要文章会陆续发表。.