青藏高原高寒草甸温室气体排放对增温和降水改变的响应

Temperature increases and precipitation changes are both expected to alter grassland ecosystem processes, such as carbon and nitrogen biogeochemical cycles. The Qinghai-Tibetan Plateau, which is regarded as the third pole of the word, is believed to be particularly sensitive to global climate changes. Alpine meadow embodies the dominant grassland type of the Qinghai-Tibetan Plateau. Therefore, it is critical to understand the effects of warming and alter precipitation to greenhouse gases in an alpine meadow (especially in non-growing season), which will contribute to assess the contribution of the greenhouse gases emissions from alpine meadow ecosystems. A two-way factorial design (warming: control, warming; precipation(50% reduction of precipitation, control, 50% increase of precipitation) was used to assess how greenhouse gases emissions are affected by warming and precipitation changes and to quantify the annual emissions from an alpine meadow on the Qinghai-Tibetan Plateau. Furthermore, we also study the effects of warming and alter precipitation on soil temperature,soil moisture, soil aggregate structure, soil mineral nitrogen and plant net primary productivity, to explore the mainly control factors of the responses of greenhouse gases on temperature increase and precipitation changes. This study will contribute to evaluate the quantity of greenhouse emission fluxes from the alpine ecosystem of the Qinghai-Tibetan Plateau under the future climate change conditions.

研究表明增温和降水的改变对草地生态系统碳、氮循环过程有着显著影响。青藏高原作为世界的第三极，被认为是气候变化的敏感区域。由于高寒草甸是青藏高原的主体，掌握增温和降水改变对青藏高原高寒草甸生态系统温室气体排放的影响机制，将有助于科学估算未来气候变化背景下青藏高原温室气体排放的贡献量。本研究依托海北高寒草甸生态系统定位站，以高寒草甸为研究对象，采用增温(对照，增温)和改变降水(减水50%，对照，增水50%)两因素完全随机区组实验设计，利用静态箱-气相色谱法，研究增温和降水改对高寒草甸生态系统生长季和非生长季尤其是冻融期温室气体排放规律的影响，量化温室气体的全年排放量；结合对土壤环境因子、团粒结构、微生物生物量、矿质氮以及植被净初级生产力等因素的研究，分析高寒草甸温室气体排放对水热条件改变的敏感性以及主要驱动因子，为准确估测未来气候变化背景下，高寒草地生态系统温室气提排放提供理论依据。

掌握增温和降水改变对青藏高原高寒草甸生态系统温室气体排放的影响机制，将有助于科学估算未来气候变化背景下青藏高原温室气体排放的贡献量.我们选择高寒矮嵩草草甸为研究对象，在增温（两水平：对照，增温）和降水改变（三水平：减水50 %，对照，增水50 %）处理下结合基因芯片技术探究了实验增温以及降水改变对温室气体排放的影响极其潜在机制。结果表明，(1) 在未来青藏高原高寒草甸气候温暖化的趋势下, 非生长季土壤冻融交替天数会显著增加，势必会影响高寒草甸生态系统土壤碳氮循环；(2）增温降低了土壤无机氮的利用效率，随着降水的增加土壤无机氮的利用效率增加，增温和降水改变主要通过改变土壤水分而不是土壤温度影响生长季土壤无机氮的利用效率；(3）土壤温度是影响CO2通量的主要驱动因素，除了直接影响CO2通量，还可以间接通过增加生态系统净初级生产力来增加生态系统CO2通量，土壤水分也是CO2通量的另一个主要影响因素。增温对CO2通量的影响取决于降水,在缺水的条件下，增温是能抑制CO2排放，而在增加降水的条件下，增温显著增加了CO2的排放；4）我们发现增温除了通过增加甲烷的氧化能力还可以抑制CH4的产生来增加CH4的吸收，增温显著增加了CH4的吸收，但是其效应大小随着降水的增加而降低。是水分而非温度决定了青藏高原高寒草甸CH4收支的情况。