内蒙古农牧交错带退耕还草温室气体收支平衡研究

Land use change which is driving the large changes of the soil carbon and nitrogen greenhouse gases CO2、CH4 and N2O exchanges is an important human factor, and it has exerted profound influence on the global climate change. Land use change happens frequently in the agro-pastoral ecotone worldwide. The studies about land use change that affected related ecological function in the agro-pastoral ecotone were more concentrated on degradation or recovery of soil and vegetation, less about the greenhouse gases emission after grassland cultivation, none about the comprehensive influences on balance of the greenhouse gases emission and absorption after the conversion from cropland to grassland in China. In the agro-pastoral ecotone of semi-arid region of Inner Mongolia, by taking the artificial grassland, which builds on the cropland, and the summer corn field, which has a serious degradation in its soil, as the research objects. This project will continuously measure the net exchanges of CO2、CH4 and N2O and their auxiliary factors in the fields for a long term. Meanwhile we will combine with the soil column incubation experiment which controlling temperature and humidity and determination of rates of N mineralization、nitrification and denitrification in order to explore the effects on the net source and sink of the three greenhouse gases fluxes after the conversion from cropland to grassland, determine its main influencing factors, and evaluate the ecological functions of the conversion from cropland to grassland on the point of Greenhouse gases balance. The research results will provide scientific foundation and decision basis to agriculture and animal husbandry sustainable development and ecological civilization construction in the agro-pastoral ecotone of semi-arid region.

土地利用变化是驱动土壤碳氮温室气体CO2、CH4和N2O交换发生大幅度改变的重要人为因素，对全球气候变化产生深刻影响。世界范围的农牧交错带经常发生土地利用变化，关于农牧交错带土地利用变化影响生态功能的研究多集中于土壤和植被的退化或恢复，对草地开垦后的温室气体排放仅有少量研究报道，而关于退耕还草对温室气体收支平衡的综合影响在国内还未见研究报道。本项目以内蒙古半干旱区农牧交错带退耕还草后的人工草地和土壤发生严重退化的夏玉米田为研究对象，开展CO2、CH4和N2O净交换通量及相关过程变量的长期野外观测，并结合控温控湿的原状土柱培养实验和土壤总矿化、硝化和反硝化速率的测定，探究退耕还草对三种温室气体源/汇净通量的影响效应，并确定其主要影响因素，从温室气体收支平衡的角度评价退耕还草的生态功能。研究成果将为半干旱区农牧交错带的农牧业可持续发展和生态文明建设提供科学基础与决策依据。

土地利用变化是驱动土壤碳氮温室气体CO2、CH4和N2O交换发生大幅度改变的重要人为因素，对全球气候变化产生深刻影响。本项目以内蒙古半干旱区农牧交错带退耕还草后的人工草地（包括禁牧割草对照（CK）、连续放牧（CG）和划区轮牧（RG）三个子处理）和土壤发生退化的农田（包括玉米地（CF）、土豆地（PP）和撂荒地（AL）三个子处理）为研究对象，开展温室气体交换通量及相关过程变量的长期野外观测，并结合控温控湿的原状土柱培养实验（在人工草地的禁牧割草对照处理和农户玉米田采集原状土柱）探究退耕还草对三种温室气体源/汇通量的影响效应，并确定其主要影响因素，从温室气体收支的角度评价退耕还草的生态功能。主要结果如下： . 通过野外原位观测发现人工草地CH4年平均吸收通量显著小于农田，表明退耕还草会减少土壤对大气CH4的吸收。农田CF处理和PP处理的N2O的累积排放量显著高于人工草地，说明退耕还草可以减少土壤N2O排放量。二者综合效应为每年草地比农田少排放温室气体248.4kgCO2ha-1（以CO2当量计，100年尺度）。.通过原状土柱培养实验发现干湿交替和冻融循环过程显著影响草地和农田土壤CH4、CO2和N2O通量。不同的降水强度处理下（相同的控制温度下），三种温室气体通量在处理间均差异显著；不同控制温度处理下（相同的降水处理下），三种温室气体通量在处理间也有显著差异。冻融循环过程对温室气体通量也有显著影响。. 可见，综合考虑CH4和N2O通量，退耕还草会显著减少温室气体排放量。土壤温度和土壤湿度是温室气体通量的两个最重要的影响因素。