黄土高原旱塬区陇东苜蓿草地N_2O释放动态及微生物驱动因子的研究

N_2O Emission Dynamics and Its Microbial Mechanism of a 3-year-old Alfalfa Grassland in the Arid Loess Plateau

在甘肃庆阳黄土高原,采用静态箱-气相色谱法测定了3年龄陇东苜蓿草地不同物候期的N2O释放通量,采用最大或然数法（MPN）测定了土壤0～30 cm硝化细菌和反硝化细菌数量,探讨旱区紫花苜蓿草地N2O释放规律与其土壤微生物的关系。结果表明：（1）3年龄陇东苜蓿草地年内N2O释放通量在-0.099～0.085 mg·m-2·h-1之间;N2O释放通量在头茬花期和越冬前再生期达到高峰,而二茬再生期和越冬期则处于N2O吸收期,成为N2O贮存库。（2）陇东苜蓿草地亚硝酸细菌、硝酸细菌和反硝化细菌数量在不同物候期和土壤层次间存在差异。（3）3年龄陇东苜蓿草地N2O释放通量与土壤水分含量、土壤pH、硝酸细菌和反硝化细菌数量间呈显著正相关线性关系。（4）庆阳黄土高原旱区陇东苜蓿草地是较弱的农业N2O释放源,远低于同类研究和国际释放平均水平。

N2O emission dynamics and its microbial mechanisms within alfalfa grassland in arid areas were previously unclear.Accordingly,gas collection was performed on a 3-year old alfalfa （Medicago sativa L.cv.Longdong） grassland in Qingyang,on the Loess Plateau,using a static,enclosed chamber.N2O emission flux was measured using High Performance Gas Chromatography.Quantities of nitrifying and denitrifying bacteria in soils at a depth of 0～30 cm were determined using the most probable number （MPN） method.The results showed：（1）The N2O emission flux of alfalfa grassland ranged from -0.099～0.085 mg·m-2·h-1 through all phonological stages.N2O emission peaked at flowering stage of the first cut and at the re-growth stage before overwintering,whereas the grassland absorbed N2O at re-growth stage of the second cut and during overwintering,which became the N2O repository.（2）The amounts of nitrite bacteria,nitrate bacteria and denitrifying bacteria varied among different phenological stages and soil layers.（3）Significant linear correlation was found between N2O emission flux and soil moisture content and soil pH value and the amounts of nitrate and denitrifying bacteria.（4）Longdong alfalfa grassland in Qingyang was found to be a weaker N2O emission source than other agricultural sources as reported in similar research and the international average of emission level.