不同放牧强度下南疆昆仑山草地生态系统N2O产生和排放的机理研究

Grassland is one of the most widely distributed vegetation type on land ecosystem. Production and emission of N2O from grassland have substantial influence on global climate change. As the major pasture for local herdsmen, grassland on the north Kunlun mountain slope in southern Xinjiang plays key role for sustainable development of local livestock. Grazing is the most important land use in grassland ecosystem, which influences N cycle in particular N2O emissions. Few studies, however, investigated N2O emissions from mountain grassland, in term of its relationship with environmental factors and response to grazing intensity. This project will target the grassland on the north Kunlun mountain slope and use the modified silicon diffusive equilibrium samplers and static-vented chamber technique for determination of N2O concentrations in soil profiles and surface emissions, respectively. In addition, molecular techniques such as the high-throughput sequencing and real time quantitative PCR will be used to monitor the changes of microbial activities. This study will quantify the effect of grazing intensity on N2O emissions from grassland, by focusing on dynamic changes of N2O production and emission from grassland under natural and grazing conditions and its relationship with environmental factors including climate, soil and associated microorganisms. This project is of great importance for estimating the source/sink contribution of grassland to atmosphere N2O emission, understanding mechanism of N2O emission from mountain grassland, and further establishment of proper grazing practices for sustainable development of grassland.

作为全球陆地分布最为广泛的植被类型之一，草地生态系统的N2O排放对全球气候变化具有重要影响。南疆的昆仑山北坡草地是当地牧民的主要牧场，对新疆畜牧业发展有关键作用。放牧是草地生态系统最主要的利用方式，对氮循环尤其是N2O排放有显著影响。目前关于高山草地的N2O排放特征与环境因子的关系及其对不同强度放牧措施的响应，研究甚少。本项目以昆仑山北坡草地为研究对象，利用改进的原位硅胶管和静态箱方法连续监测土壤剖面N2O浓度和地表排放的动态变化，应用高通量测序和PCR监测相关微生物活性，定量分析放牧对草地N2O排放的可能影响，从而系统研究自然及不同放牧强度下草地土壤N2O产生和排放特征及其与环境因子包括气候、土壤和相关微生物的关系。本项目实施对于正确评价草地土壤对大气N2O的源汇贡献、理解N2O排放机理、制定合理的放牧措施具有重要意义。

位于我国新疆南部昆仑山北坡的高山草地是当地牧民的主要牧场，对新疆的畜牧业发展有关键作用。在过去几十年中，过度放牧已经导致该地区草原严重退化。为了减缓和防止草原进一步退化，诸如降低放牧强度、轮牧和封牧等措施已经实施。目前关于放牧如何影响草地生态系统的N循环尤其是N2O排放和潜在的微生物机制的研究甚少。本项目利用改进的原位硅胶管和静态箱方法连续监测土壤剖面N2O浓度和地表排放的动态变化，应用高通量测序和PCR监测相关微生物活性，明确了放牧对草地N2O排放的影响及其驱动因子。主要研究结果表明：1）与重度放牧相比，轻度放牧显著减少了生长季N2O 累积排放量，并增加了牧草地上生物量和N 吸收，表明适当的放牧强度对减少N2O排放、维持高山草地可持续生产具有重要意义；2）高山草地土壤N2O排放主要受环境因子包括土壤温度、湿度和C含量控制，而与硝化和反硝化相关功能基因丰度的关系不大；3）与单施N肥相比，适度的N、P同时添加能够在提高草地生产力的基础上，维持土壤微生物群落多样性，并显著降低N2O排放。本项目的研究结果为制定合理的高山草地养分管理以及放牧措施提供了科学依据。