黄土高原旱作农田净综合增温潜势对降水变化的响应机制

Precipitation event has a short priming effect on greenhouse gas (CO2, N2O, and CH4) (GHG) emissions under dryland cropping systems which may affect the long-term net global warming potential (GWP) in the arid and semiarid areas. In this project, we will quantify the effects of precipitation intensity, frequency, and seasonal and annual distribution on GHG emissions and net GWP under a winter wheat-fallow cropping system by using the rainfall-manipulated technique in the Loess Plateau. The relative importance of "substrate supply" and "microbial stress" mechanisms in responding of GHG emissions to precipitation will be evaluated by analyzing changes in soil carbon and nitrogen fractions, enzyme activity, microbial biomass and activity, and microbial community structure during soil drying-wetting cycles due to precipitation events. The response of root respiration and crop production to precipitation will also be measured to elucidate the trade-offs between crop yield formation, water and nitrogen use and net GWP as being stimulated by precipitation events under dryland cropping systems. The results will provide a better understanding of carbon and nitrogen cycles in the agroecosystem and their interaction with climate change in the arid and semiarid areas. The experiment will also provide opportunity to develop novel management techniques to reduce GHG emissions and GWP, increase C sequestration, and sustain dryland crop yields in the Loess Plateau.

降水事件对旱作农田土壤温室气体排放过程具有显著但短暂的激发效应，这可能进一步影响到长时间尺度的生态系统净综合增温潜势。项目拟以黄土高原旱作冬小麦农田为例，基于人工控制降水系列试验和长期定位试验，通过改变降水量、强度、频率和季节分布，在田间系统观测的基础上，分析旱作农田土壤温室气体(CO2、N2O、CH4)对降水变化的动态响应规律，确定降水激发效应对农田净综合增温潜势的贡献；通过分析降水前后土壤不同形态碳/氮浓度、微生物活性和群落结构变化，阐明"底物供给"和"微生物胁迫"两种机制的相对重要性及其微生物功能响应机理；并在此基础上，通过研究不同降水模式下的根系呼吸和作物产量形成过程，揭示作物产量-水氮利用效率-净综合增温潜势之间的耦合关系。项目预期结果可以深化对旱作农田生态系统碳氮循环过程及其与气候变化交互作用机制的理解，并为黄土高原地区农田固碳减排管理实践提供重要的理论支撑。

降水对旱作农田土壤温室气体排放过程具有显著但短暂的激发效应，并进一步影响到长时间尺度的生态系统净综合增温潜势。项目以黄土高原旱作冬小麦农田为对象，基于人工控制降水系列试验和定位试验，通过改变降水格局，系统研究了旱作农田土壤温室气体 (CO2、N2O、和CH4) 排放对降水变化的响应过程及其机制。项目取得的主要成果有：①增加降水量导致土壤CO2排放增加，降水激发“Birch效应”效应增强，也能够在短期内导致旱作农田土壤由CH4“汇”向“源”转变。作物生长期间土壤“Birch效应”的响应机制主要以“微生物胁迫”为主，而夏季休闲期，土壤响应机制则随着降水量的增加由“微生物胁迫”转变为“底物供给”。②增加降水频率可以通过增加土壤含水量刺激土壤CO2释放，较高降水频率下土壤CO2释放在初次降水时以“底物供给”机制为主，而末次降水时则转为“微生物胁迫”机制为主。③旱作冬小麦农田综合增温潜势、作物产量和温室气体排放强度与降水增加量之间均存在极显著相关关系，生育期增加降水强化了农田土壤作为大气CO2和N2O源的特征，然而增加降水也刺激了作物生产，其所产生的补偿效应使旱作冬小麦农田系统由温室气体排放的源转为了汇。④与自然降水相比，夏闲期控制减半降水显著降低了系统净增温潜势和温室气体排放强度，而填闲种植则较裸地休闲显著促进了温室气体排放和净综合增温潜势。种植长武怀豆较黑麦草单播或混播处理具有更低的温室气体排放强度，可以考虑在黄土高原地区夏闲期推广种植。相关成果深化了对旱作农田生态系统碳氮循环过程及其与气候变化交互作用机制的理解，为黄土高原地区农田固碳减排管理实践提供了重要的理论支撑。