城乡梯度绿地土壤温室气体排放的时空变异及驱动机制

Urban area expansion rate is much higher than its population growth, becoming one of the most significant changes in the world. The study on urban-to-rural gradient has be considered an effective tool to reveal the driving mechanism of urban ecosystem ecological process and function. Green space is the most important element of city landscape structure, its greenhouse gas emissions not only directly affect the city environment quality, may also be the unknown global greenhouse gas source. We choose the main green spaces along the urban-to-rural gradient in Nanchang, a rapid urbanization and ecological garden city, to study spatial and temporal variation of soil greenhouse gas emissions. We will establish three experimental platforms including in situ continuous monitoring, laboratory incubation and driving factor control experiments, and determine CO2, CH4 and N2O fluxes using the static opaque chamber and gas chromatography method, analyze the functional diversity of microorganisms using high-flux sequencing method, measure enzyme activities using automatic ELISA, and analyze soil carbon and nitrogen variables. Therefore, we try to understand the driving mechanisms of urbanization on soil greenhouse gas emission in green spaces along the urban-to-rural gradient, and the interactions among soil CO2, CH4 and N2O emissions, based on the comprehensive information about green space types, dominant plant attributes, atmospheric environments and so on. Our results may be helpful to provide important references of improving green space construction, urban living environment and estimating global greenhouse gas balance.

城市面积扩张速度远高于其人口数量增长，成为全球最显著的变化特征之一。城乡梯度研究是最新兴起揭示城市生态过程与功能驱动机制的有效工具。绿地是城市园林最重要的空间结构元素，其土壤温室气体排放不仅直接影响城市人居环境质量，也可能是全球温室气体源汇平衡的未知者。本研究以快速城市化代表、生态园林城市南昌为案例，选择城区－郊区－乡村梯度主要绿地为对象，建立原位连续监测、室内恒温培养、驱动要素控制等实验平台，采用静态暗箱-气相色谱仪法测定CO2、CH4和N2O通量，高通量测序分析微生物功能群多样性、全自动酶标仪测定土壤酶活性、化学分析法测定土壤碳氮等变量，综合绿地类型、优势植物属性、大气环境等特征，统计分析和模拟验证相结合，揭示城乡梯度绿地土壤温室气体排放时空变异的规律，阐明城市化对绿地土壤CO2、CH4和N2O排放及关联耦合的驱动机制，为提升绿地建设水平，改善城市人居环境、估算全球温室气体平衡提供参考

城市化是人类社会经济发展的必然趋势，但同时给城市生态系统带来巨大压力和挑战。樟树林作为重要绿化用树种之一，绿化应用十分普遍。施凋落物作为养分循环的固有部分，会显著影响土壤温室气体（GHG）排放。因此，深入探究凋落物等对城乡梯度绿地土壤GHG排放的影响和机理，对制定城市绿地GHG减排措施具有重要意义。本研究同时结合毛竹、乌桕、草地等与城乡梯度相关的绿化带进行了GHG排放研究。.采用静态箱-气相色谱法，监测南昌城乡梯度樟树林土壤GHG排放。采用分解袋法研究氮肥添加对城乡梯度樟树林凋落物分解的影响。结论如下：1）城乡梯度处理下，城区-郊区-农村的樟树林土壤N2O和CO2排放均有显著差异性。其中，城市樟树林土壤N2O的排放分别比郊区和农村土壤高105% 和196%，农村CO2的排放速率要显著高于城区。2）氮肥添加后，土壤N2O和CO2排放出现明显的峰值。氮添加显著增加土壤N2O排放，但总体上对CO2排放没有显著影响，CO2排放呈现出季节性动态变化。3）凋落物去除可以显著降低樟树林土壤CO2的排放但分别增加了 59.7%、50.9% 和 43.3%的城市、郊区和农村土壤N2O的排放。当凋落物和氮添加交互时，土壤N2O的排放显著增加，但对CO2的排放无影响。4）城区-郊区-农村的樟树林土壤amoA细菌和古菌的基因和反硝化细菌（nirK、nirS和nosZ）的基因拷贝数存在有显著差异，其中城区土壤的微生物基因丰度显著高于郊区和农村。城区樟树林土壤N2O和CO2的排放较高。裸露的林地地表会增加樟树林土壤GHG的累积排放量。在人工林经营管理中应避免出现裸露的林地，保持凋落物在地表的自然覆盖。在林地施肥时，要注意城乡梯度上不同位置开展针对性施肥和凋落物管理，减少城市人工林土壤GHG排放。在追求经济效益的同时，也要充分发挥林业的生态效益。基于城乡梯度绿地的重要作用，应综合绿地管理方式以及环境因子，进一步提高绿地减排增汇潜力，减少绿地GHG排放，提高其在缓解气候变化方面的生态学效益。