冻融格局变化和放牧对半干旱草原土壤氮素循环关键过程的交互影响效应与机制

Soil freeze-thaw pattern and grassland ecosystem have been dramatically changed due to the global climate change and growing human activities during last decades, which in turn would have significant impact on the key processes of soil nitrogen cycling. Although China has a vast area of seasonal frozen soil, very little is known about the interaction effects of soil freeze-thaw and grazing on grassland soil nitrogen cycling and the underlining mechanisms. In this study, therefore, the Hulunbuir grassland is selected as the key study area. Based on the in situ and laboratory incubation experiments, nitrogenous gases (N2O,NO and N2) emission from soil and the key processes of soil nitrogen cycling, as well as the realted microbial characteristics will be determined by using the gas-flow-soil-core technique, molecular microbial ecology method and isotope technique.The main objectives of this study are: (1) to reveal the interaction effects of soil freeze-thaw pattern and grazing on the key processes of soil nitrogen cycling and nitrogenous gas emissions; (2) to identify the key environmental and edaphic factors that affect these interactions; (3) to determine the underlining microbial mechanisms of the key processes of soil nitrogen cycling and nitrogenous gas emissions responded to different soil freeze-thaw patterns and grazing. These results are expected to provide scientific references for evaluating the combined effects of soil freeze-thaw and garzaing on the key processes of soil nitrogen cycling in the semi-arid grassland of China and forecasting the response to future climate changes.

随着全球气候变化和人类活动的不断加剧，土壤冻融格局和草地生态系统会发生显著的变化，这将进一步对土壤氮素循环关键过程产生深远的影响。虽然我国季节性冻土面积广阔，但关于冻融作用和放牧对草地土壤氮素循环过程交互影响效应的研究仍十分缺乏，导致对其内在影响机制尚不清晰。本项目以内蒙古呼伦贝尔草原为研究区，结合野外观测和室内培养实验，采用直接测定N2法、微生物分子生态学法和同位素技术等方法，测定冻融格局变化和放牧条件下土壤含氮气体排放(N2O、NO和N2)和氮素循环关键过程转化速率以及相关微生物特性，揭示冻融格局变化和放牧对土壤氮素循环过程和含氮气体排放的交互影响效应，明确影响该效应的关键土壤和环境因子，解析冻融格局变化和放牧对土壤氮素循环关键过程和含氮气体排放影响的微生物机制，从而为科学评估土壤冻融和放牧对我国半干旱草原土壤氮素循环关键过程影响的综合效应以及为预测其对未来气候变化的响应提供科学依据。

虽然我国季节性冻土面积广阔，但关于冻融作用和放牧对草地土壤氮素循环过程交互影响效应的研究仍十分缺乏，导致对其内在影响机制尚不清晰。本项目以内蒙古呼伦贝尔草原为研究区，采用直接测定N2法和微生物分子生态学等方法，测定了冻融格局变化和放牧条件下土壤含氮气体排放和氮素循环关键过程的微生物特性，揭示了冻融格局变化和放牧对土壤氮素循环过程和含氮气体排放的交互影响效应，明确了影响该效应的关键土壤和环境因子。主要研究结果表明：.1）冻融格局变化显著促进了土壤可溶性有机碳、铵态和硝态氮、微生物生物量碳氮的含量。而放牧显著降低了土壤冻融过程中可溶性有机碳、可溶性有机氮、铵态氮的含量，但是对其它土壤指标的影响不显著。 .2) 冻融格局变化对硝化微生物和反硝化微生物的丰度没有显著性影响。重度放牧显著降低了氨氧化古菌和cnorB，nosZ类型反硝化微生物的丰度，轻度放牧显著促进了cnorB类型反硝化微生物的丰度。 .3) 内蒙古草甸草原土壤三种含氮气体的排放通量在冻融循环期间均显著增加，但放牧显著降低了土壤冻融期间三种含氮气体的累计排放通量。因此，冻融作用和放牧对土壤氮素循环过程和含氮气体排放存在明显的交互影响效应。.4）影响因素和作用机制的分析表明，土壤充水孔隙度、DOC:NO3-比值显著促进了土壤冻融过程中N2O的排放通量，而且还可通过间接影响nirS和cnorB类型反硝化微生物的丰度影响土壤冻融过程中N2O的排放速率，而放牧会通过降低DOC:NO3-比值对土壤冻融期间N2O的排放速率产生负向影响。此外，放牧可通过影响DOC:NO3-比值对于NO排放速率有直接影响，以及通过WFPS影响nirS类型反硝化微生物的丰度间接影响NO的排放速率。放牧会通过影响DOC:NO3-比值和WFPS来间接影响冻融过程中cnorB和nosZ类型反硝化微生物的丰度从而降低N2的排放速率。.项目在Biology and Fertility of Soils，Geoderma，Frontiers In Ecology And Evolution，Catena等重要国际期刊发表了6篇SCI论文，中文核心期刊论文2篇，还有3篇SCI论文尚在审稿和撰写中，完成了既定的任务和目标。