氮素富集对高寒草甸土壤CH4吸收和N2O排放耦合作用的影响机理

There is a complex linkage between methane (CH4) uptake and nitrous oxide (N2O) emission from water unsaturated soils, but the mechansims responsible for the effects of nitrogen enrichment on their coupling are still unclear. In this project, an alpine meadow ecosystem on the Qinghai-Tibetan Plateau will be selected as a case to conduct a low-level and multi-form N addition experiment. First，based on both methods of static chamber-gas chromatography and stable isotopic abundance gradient in soil profile，we will measure and compute the soil-atmospheric fluxes of CH4 and N2O,the oxidation ratio of CH4, and the contribution proportion of nitrification and dinitrification to soil N2O， which will be useful to clarify long-term responses of soil CH4 uptake and N2O emission to the increased nitrogen deposition, and to analyze the relationships between soil CH4 oxidation, N2O production in soil profile as well as to compute the net exchange fluxes of CH4 and N2O between soil and atmosphere. Second,based on the microcosm incubation experiment extracting functional genes pmoA and amoA，the T-RFLP, cloning and sequencing techniques are used to determine the rates of soil CH4 oxidation and N2O production, and the quantity and composition of soil methane oxidizing bacteria (type I and type II) and ammonia oxidizing bacteria and archaea(AOB and AOA) communities，which will be helpful to clarify the interaction between soil functions (i.e.,CH4 oxidation and N2O production) and key functional microbial communities (i.e., methane oxidizing bacteria and ammonia oxidizing microbes), and to reveal the microbial mechanisms involved in the responses of soil CH4 uptake and N2O emissions to the increased nitrogen deposition.Above results of two studies scale will help us to understand the"seesaw effect"between carbon and nitrogen fluxes and productivity in terrestrial ecosystems, and to improve the biogeochemical processes models of carbon and nitrogen cycles, and as well as to control or decrease greenhouse gas emissions from the alpine meadow soils on the Qinghai-Tibetan Plateau.

水分非饱和土壤CH4吸收和N2O排放之间存在复杂的联动关系，两者之间的耦合作用及其对增氮的响应机制尚不清楚。本项目以青藏高原高寒草甸为研究对象，基于多形态的增氮控制试验，利用静态箱-气相色谱法和稳定性同位素梯度法测定并计算地表CH4和N2O净交换通量、土壤剖面CH4氧化比例和N2O来源贡献，阐明土壤CH4吸收和N2O排放对增氮的长期响应规律，量化土壤剖面CH4氧化、硝化和反硝化过程对地表净交换通量的贡献。构建微宇宙培养实验，利用基于功能基因pmoA和amoA的T-RFLP和克隆测序技术，研究土壤CH4氧化、N2O产生速率与甲烷氧化菌、氨氧化菌群落数量和组成之间的关联，揭示土壤CH4吸收和N2O排放的耦合作用及其对增氮响应的微生物学机理。研究结果有助于深入理解陆地生态系统碳氮通量与生产力之间的"跷跷板"效应, 完善碳氮生物地球化学过程模型，并可为控制青藏高原高寒草地温室气体排放提供理论依据。

水分非饱和土壤CH4吸收和N2O排放之间存在复杂的联动关系，两者之间的耦合作用及其对增氮的响应机制尚不清楚。本项目以青藏高原高寒草甸为研究对象，基于多形态的增氮控制试验，利用静态箱-气相色谱法和稳定性同位素梯度法测定并计算地表CH4和N2O净交换通量、土壤剖面CH4氧化比例和N2O来源贡献，阐明土壤CH4吸收和N2O排放对增氮的长期响应规律，量化土壤剖面CH4氧化、硝化和反硝化过程对地表净交换通量的贡献。构建微宇宙培养实验，利用基于功能基因pmoA和amoA的T-RFLP和克隆测序技术，研究土壤CH4氧化、N2O产生速率与甲烷氧化菌、氨氧化菌群落数量和组成之间的关联，揭示土壤CH4吸收和N2O排放的耦合作用及其对增氮响应的微生物学机理。主要研究结果如下：①氮素富集会改变放牧高寒草甸土壤氮素有效性和分配格局（铵匮乏+硝富集），长期铵态氮输入（＞25kg N ha-1 yr-1）会导致土壤氮素耗竭；土壤初级氮转化速率和氮转化功能微生物群落丰度对增氮的响应取决于施氮类型和剂量，施氮加剧了放牧高寒草甸土壤氮转化过程的解耦；高寒草甸土壤惰性有机氮矿化、自养硝化与土壤氨氧化、反硝化细菌种群丰度对增氮的响应并不完全一致，两者的耦合关系表现形式多样。②氮素有“好氮”与“坏氮”之分，NH4+富集加剧土壤酸化，抑制土壤CH4吸收，促进N2O排放均显著强于NO3-，生态负效应更大。氮素富集条件下，硝化作用与土壤酸化的循环往复正反馈过程是高寒草甸土壤碳氮气体通量响应的核心，其他过程均受这个反馈过程的影响或控制。③施氮7年显著改变青藏高原高寒草甸土壤真细菌和古菌基因丰度和群落组成，取决于施氮类型和施氮剂量。施氮加剧了真细菌和古菌群落的分异，低氮增加而高氮降低真细菌和古菌的多样性，临界氮沉降量为20kgN ha-1 yr-1。此外，(NH4)2SO4的影响显著高于KNO3和NH4Cl，可能与土壤酸化有关。研究结果有助于深入理解陆地生态系统碳氮通量与生产力之间的“跷跷板”效应, 完善碳氮生物地球化学过程模型，并可为控制青藏高原高寒草地温室气体排放提供理论依据。