高寒泥炭湿地土壤碳稳定性对氮沉降的响应机制研究

Abstract: Due to the coupling effect of carbon and nitrogen, atmospheric nitrogen deposition may alter the global carbon cycle and, as a result, influence global climate change. However, the mechanisms nitrogen effects on soil organic carbon stability and carbon sequestration potential in nitrogen-limited plateau peat wetland of nitrogen limitation remain unclear. In this project, the plateau peat wetland soil will be investigated in order to reveal the variation in the chemical structure and stability of soil organic carbon through such methods as adding nitrogen and tracing 13C and 15N -from isotopically labeled plant residues. The objectives of our study are to: 1) test whether simulated nitrogen deposition increases net CO2 emissions and promotes the decomposition of litter and soil organic matter; 2) identify processes contributing to accumulation or turnover of different components or chemical structure changes of soil organic carbon; 3) examine responses to elevated N by microbial biomass,communities,and extracellular enzymatic activity. The results of this study will elucidate effects of N inputs on soil organic carbon stability in alpine peat wetlands. This project may also contribute to effective ways to enhance terrestrial ecosystem carbon sequestration potential by strengthening biochemical stability of carbon of peat wetlands and help to theoretically develop and improve terrestrial ecosystem carbon cycle models.

由于碳氮的耦合作用，大气氮沉降可能会改变全球碳循环，加剧/减弱全球气候变化。对于受氮限制的高寒泥炭湿地，氮沉降对土壤有机碳稳定性和碳汇潜力的作用机理尚不清楚。本项目以若尔盖泥炭湿地土壤为研究对象，通过增氮控制试验、同位素示踪等方法，模拟氮沉降是否通过促进凋落物和土壤有机质的分解而增强土壤CO2的净排放；对比研究对照样地和增氮样地不同组分有机碳累积过程和土壤有机碳化学结构的变化；区分新增的和原有的微生物量碳对增氮的响应，并进一步研究土壤微生物群落结构、胞外酶活性的变化，从微生物的角度揭示氮沉降对土壤有机碳稳定性的影响机制。研究结果将对准确评价氮沉降对高寒泥炭湿地碳稳定性的影响提供科学依据，有助于寻找通过提高泥炭湿地碳的生化稳定性来增强陆地生态系统碳汇潜力有效手段，并可为陆地生态系统碳循环模型的完善和发展提供理论依据。

土壤有机碳库在全球碳循环中具有重要作用，大气氮沉降可能通过碳氮耦合作用改变全球碳循环。本项目以若尔盖泥炭湿地土壤为研究对象，通过增氮控制试验，探究氮沉降对典型高寒泥炭湿地土壤碳稳定性和碳汇潜力的影响。结果表明：氮添加提高泥炭湿地土壤碳矿化和温室气体排放速率以增加碳输出，但同时增加生物量碳储量和凋落物碳输入量，使土壤整体呈现“氮促碳汇”规律，使高寒泥炭湿地土壤在氮沉降背景下成为新的碳汇；氮添加影响土壤中有机碳稳定性，增加了土壤可溶性碳组分含量，促进土壤碳周转过程，活跃土壤中碳素转化动态；氮添加改变了土壤微生物群落结构，提高土壤微生物群落丰富度和功能多样性。通过提高土壤碳转化相关酶活性，影响土壤中碳输入和输出动态过程，进而影响土壤中的碳稳定。本研究有助于准确评价氮沉降对泥炭湿地土壤碳截留和碳汇功能，为政府制定相应的控制CO2排放的发展战略提供科学依据，对全球元素循环及平衡有着极为重要的环境意义。