华北农田N2O排放及其产生的关键过程对灌溉水盐的响应

Farmland is the most important nitrous oxide (N2O) emission source related with human activity. In recent years, for releasing the increased water resources scarcity, the amount of underground saline water used for irrigation is rapidly increasing in China. Saline water irrigation will bring considerable salt into soil, which may affect soil extracellular enzyme activity, function of microbial community related closely with soil nitrogen transformation, and soil N2O emission. Therefore, investigating the changes of farmland N2O emission and exploring relevant mechanisms under different saline irrigation water application are crucial for estimating accurately regional N2O emissions in areas with increasing saline water irrigation. N2O emission of cotton field in Hebei Low Plain area is set as research object, and manipulative soil moisture and salinity situations are established with combining several irrigation scheduling and irrigation water salinity in this research. During whole cotton season and following fallow period, N2O emission is monitored on field continually, combined lots of relevant incubation experiments in laboratory, to show the characteristics of N2O emission and to explore the changes of paths related to N2O production (i.e. extracellular enzyme activity, function of microbial community and functional genes). The main purpose of this project is to determine effects of irrigation scheduling and water salinity on soil N2O emission in cotton field and to reveal the relevant microbiological mechanisms, which is helpful for assessing regional agricultural N2O emissions accurately, and developing suitable saline water management strategy for high yield, sustainable crop production and less N2O emission in future.

农田是N2O最为主要的人为排放源。近年来，随着我国水资源短缺不断加剧，利用地下咸水资源灌溉的农田迅速增多。咸水灌溉会给土壤引入大量盐分，影响涉及土壤氮素转化相关微生物活性，进而改变N2O排放。因此，开展不同灌溉水盐条件下农田N2O排放的研究，对于未来咸水灌溉农田面积增加背景下准确估算区域N2O排放具有重要意义。本研究拟以河北低平原区棉田N2O排放为主要研究对象，通过设置不同的灌溉水盐梯度，构建多样化的土壤盐分和水分含量模式。在棉花整个生育期对N2O排放规律进行连续监测，结合大量室内培养试验对N2O关键生成过程相关的土壤胞外酶活性、微生物群落及功能基因进行解析，以量化不同灌溉水盐条件下N2O排放差异，阐明N2O关键生成过程对灌溉水量及含盐量的响应机理，为未来该区域农田N2O排放的精准评估，以及制定既可保证作物高产和可持续生产的水分需求，又能有效减N2O排放的适宜咸水灌溉策略提供理论依据。

农田是温室气体重要排放源之一，开展农田温室气体排放相关研究，对于实现农业单元温室气体减排，减缓气候变化具有重要意义。本研究以河北黑龙港地区淡水资源短缺为研究背景，以咸水/微咸水安全利用为研究目标，探讨咸水（微咸水）灌溉对棉田土壤温室气体排放的影响，研究结果将有助于消除该区域因灌溉水质变化而带来的温室气体排放评估不确定性，并实现区域温室气体排放的精准评估，对揭示咸水灌溉的环境效应具有重要意义。本试验设计1、2、4、6、8、10g·L-1共6个灌溉水质梯度处理，系统研究了咸水灌溉对棉田土壤温室气体、土壤理化性质，土壤关键酶活性等指标的影响。主要研究结果如下：.（1）揭示了咸水灌溉对棉田温室气体排放的影响效应.对照处理下土壤CO2、CH4和N2O平均排放速率分别为332.47 mg·m-2·h-1、-16.50 μg·m-2·h-1和61.83 μg·m-2·h-1。相比对照，咸水灌溉能显著降低土壤CO2、N2O平均排放速率和CH4平均吸收速率。随着灌溉水矿化度的升高，土壤CO2、N2O累积排放通量均呈递减趋势，且高矿化度灌溉水处理下CH4累积吸收通量显著低于淡水灌溉处理。除此之外，棉田全球增温潜势（GWP）也随灌溉水浓度升高而逐渐降低，GWP最大值出现在对照处理（13060.88 kg·hm-2），最小GWP值出现在高盐处理（6026.58 kg·hm-2）.（2）阐述了咸水灌溉对棉田土壤胞外酶活性和微生物的影响.不同矿化度咸水灌溉明显改变了棉田土壤胞外酶活性。与淡水灌溉相比，咸水灌溉下土壤木糖苷酶活性、β葡萄糖苷酶和磷酸酶活性降低，而纤维素二糖酶、α葡萄糖苷酶和乙酰氨基葡萄糖苷酶活性增强。同时，咸水灌溉也改变了土壤微生物对碳源的利用能力，试验表明高矿化度灌溉水处理下土壤微生物活性显著低于淡水灌溉。.（3）咸水灌溉下温室气体排放与土壤环境因子间相互关系.土壤CO2、N2O排放量和CH4吸收量与土壤含水率、电导率、pH和铵态氮含量间存在显著负相关关系，与土壤有机质和硝态氮含量存在显著正相关关系。有关温室气体与土壤胞外酶和微生物活性间相互关系有待今后进一步深入研究。