冻融交替对高寒草甸N2O排放的影响及发生机理

Alpine meadow embodies the dominant type of Tibetan plateau,and it was realized that alpine meadow was the source of nitrous oxide.Furthermore, seasonal freeze-thaw interaction was the main climate character on Tibetan plateau.Therfore the effect of freeze-thaw on nitrous oxide would be studied in alpine meadow. Consequently, it was the basilic fund item for comprehensive assessment the response of alpine meadow under global change condition.The nitrous oxide emission flux from freeze-thaw,growing season and dormancy period, and the soil physical character,and enviromental factors were analyzed in situ monitoring, acetylene inhibation and in vitro culture. Theres were aimed to reveal the effect of freeze-thaw and their temperature and freeze time on nitrous oxide emission rate. These were studied that the ratio of nitrous oxide from freeze-thaw to the annual flux，and the contribution of nitrous oxide vs nitrogen, and the quantity of N emission from nitrification and denitrification, and the ratio of nitrous oxide and nitrogen. The contribution of nitrification and denitrification were distinguished by acetylene inhibation and field monitoring. The mechanism of freeze-thaw peocess on nitrous oxide emission were analyzed in this study from alpine meadow by soil organic,mineral nitrogen,aggregate and bulk porosity.Thus, theres contributed to all-round comprehension of N cycle, and to evaluate the quantity of nitrous oxide emission flux. There conduced to explore the feasible mitigation approach.

高寒草甸是青藏高原的主体，为大气温室气体N2O的排放源，季节性冻融为该地区最明显的气候特征之一，解析冻融交替过程中高寒草甸N2O排放通量及其与环境因子之间的耦合关系，将有助于加深对青藏高原高寒草甸N20排放特征、氮循环的认识。本项目以矮嵩草草甸为研究对象，采用密闭箱-气相色谱法和乙炔抑制法，通过田间原位监测和室内培养试验，重点研究冻融交替对高寒草甸N2O排放速率的变化规律的影响、与土壤性状、地表特征和环境因子之间的关系；量化冻融过程土壤N2O排放量，硝化和反硝化作用对N2O的贡献、反硝化过程N2排放等氮素界面过程；阐明土壤有机质、矿质态氮、土壤团聚体、总孔隙度与冻融过程的土壤硝化和反硝化作用的耦合关系；探讨冻融交替作用对高寒草甸N2O排放影响的发生机理，解析适宜的减排措施。为准确评估青藏高原高寒草甸温室气体N2O排放通量及其对冻融过程的响应提供科学依据。

高寒草甸是青藏高原的主体类型之一，在高原地区广域分布，季节性冻融为该地区最明显的气候特征之一，解析冻融交替过程中高寒草甸N2O排放通量及其与环境因子之间的耦合关系，将有助于加深对高寒草甸生态系统N2O排放特征、氮循环的认识。. 高寒草地土壤N2O排放基本呈现“高-低-高-低”的脉冲式排放特征，生长季N2O排放速率明显高于休眠季排放速率。冻融交替期间高寒草甸N2O排放速率明显高于休眠季排放速率，略低于生长季排放速率，冻融交替作用对高寒草地土壤N2O排放存在激发效应。冻融交替期间高寒草甸土壤硝化作用和反硝化作用均较强，但以反硝化作用为主，观测到较多N2排放。生长季硝化作用潜势活跃而反硝化作用强度较低。休眠季土壤N2O排放以反硝化为主导过程。. 高寒草甸土壤在冻结1个月期间，相比于对照处理，-10 ℃和-5 ℃冻结的草地土壤N2O排放速率分别降低到 0.76 ± 0.22和0.91 ± 0.28 g kg-1 h-1 (p<0.05)。冻结土壤融化过程，-10 ℃ 和 -5 ℃冻结草地土壤N2O排放速率分别为对照处理的1.81倍和2.08倍(p<0.05)。冻结土壤融化过程，显著地激发了高寒草甸土壤N2O排放通量。随着冻融交替循环次数从1次增加到12次，高寒草甸土壤N2O排放速率明显增加，从最初的1.23增加到3.34g kg-1 h-1 (p<0.05)。从第12次到第24次冻融循环时，高寒草甸土壤N2O排放速率开始下降，从3.34 降低到2.28 g kg-1 h-1，降低幅度达到31.7%。WNMM模型可以很好地捕捉到，高寒草地土壤N2O排放速率峰形及峰值变化规律，回归方程的拟合系数，R2分别达到0.66 和0.32(p<0.05)。模型对于高寒草甸土壤N2O年排放量的拟合相对偏差低于5%。2013年和2014年高寒草甸土壤硝化作用强度分别为72.8%和64.8%。未来全球增温、干旱将增加高寒土壤N2O年排放量，但降水量适度增加时，高寒草地土壤N2O年排放量降低，会这将有助于青藏高原地区高寒草地N2O减排目标的实现。. 项目组发表SCI论文4篇（含主持人第一且通讯作者2篇），协助培养博士研究生1名，培育提升了青年骨干研究人员的学术科研能力，建立了与国际和国内同行共同合作进行高寒草甸与全球变化相关研究基础。