地膜覆盖对农田生态系统温室气体排放的影响研究

The clear plastic film mulching has the roles of raising soil temperature, resisting drought and conserving soil moisture, enhancing photosynthesis, keeping soil fertility, suppressing weed, and increasing the production, etc. At present, the area of covering plastic film in croplands in China is over 13 million ha every year. Nowadays, under the background of global climate warming, the drought happens in frequently, which will increase the using area of mulching plastic film more and more. After the plastic film mulching, the ecological factors in it, such as soil temperature, sunlight, water, fertility, and soil gas components will change, which will cause the change of the production, transferring and emission of carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O) in cropland ecosystem, but there have limited reports about them. In this project, we will take the local prevailing tillage systems from Southwestern China, such as rice and wheat rotation field, dryland and vegetable plot as the subject investigated, contrasting with the no mulching systems, using the static chamber/GC method, studying on the emission characteristic and the controlling factors of CO2, CH4 and N2O releasing from fields mulched by plastic film, the contcentration characteristic of CO2, CH4 and N2O in different soil deepth. And combing with the analysis in indoor lab, studing the dynamic charcteristic of some factors, such as soil ammonium nitrogen, nitrate nitrogen, soil organic carbon, dissolvable organic carbon, microbial biomass carbon, nitrate reductase and nitrite reductase. In doing this, we will find the equation between the emission flux of CO2, CH4 and N2O in the fields of mulching plastic film with the various main controlling factors, assessing the emission amount of CO2, CH4 and N2O and the global warming potential (GWP) of the emission of three gases in an integrated manner. We expect to offer a theoretic base for the decreasing GHGs emission and increasing the fixed carbon from croplands of China.

地膜覆盖栽培具有提高地温、抗旱保墒、保肥、抑草和高产、稳产等作用，目前我国每年农田地膜覆盖面积已达1300万hm2以上。在当今全球气候变暖的背景下，干旱频繁发生，地膜覆盖面积还将增大。地膜覆盖后，膜内土壤温、光、水、肥、气等生态条件都发生了变化，这将对土壤CO2、CH4和N2O的产生、传输和排放产生影响，目前尚缺少这方面研究。本项目以我国西南地区常见的水-旱轮作农田、四季旱地和菜地为研究对象，以不覆膜农作为对照，研究地膜覆盖农作下农田生态系统CO2、CH4和N2O的排放特征及其控制因子，不同耕层土壤CO2、CH4和N2O的浓度特征；结合室内分析，研究地膜覆盖下农田土壤碳氮组分和土壤酶的动态特征，揭示土壤温度、水分、土壤碳氮组分、土壤酶、肥料施用量等因素的影响机制；估算地膜覆盖下农田生态系统CO2、CH4和N2O排放量及由此引起的综合GWP，为我国农田温室气体减排及增加土壤固碳提供理论依据。

地膜覆盖栽培具有提高地温、抗旱保墒、保肥、抑草和高产、稳产等作用，目前我国每年农田地膜覆盖面积已达1300万hm2以上。在当今全球气候变暖的背景下，干旱频繁发生，地膜覆盖面积还将增大。地膜覆盖后，膜内土壤温、光、水、肥、气等生态条件都发生了变化，这将对土壤CO2、CH4和N2O的产生、传输和排放产生影响，目前尚缺少这方面研究。本项目以稻-油轮作农田和辣椒-萝卜轮作菜地为研究对象，以不覆膜为对照，研究地膜覆盖农作下农田生态系统CO2、CH4和N2O的排放特征及其控制因子，不同耕层土壤CO2、CH4和N2O的浓度特征。结果表明，对于菜地，观测期内CH4排放通量的均值分别为-7.64和-9.00μg•m-2h-1，CH4净吸收量年均值分别为-0.54和-0.64kg•hm-2，表明地膜覆盖在一定程度上能削弱了土壤作为CH4汇的能力。在辣椒季，不覆膜处理N2O的平均排放通量为1000.0μg•m-2h-1，覆膜处理为400.6μg•m-2h-1，覆膜显著低于常规处理（P<0.05）；而在萝卜季，N2O的平均排放通量则表现为覆膜处理（128.1μg•m-2h-1）高于常规处理（107.8μg•m-2h-1）。在各土层浓度观测方面，发现两种种植方式在整个观测周期内各土层CH4和N2O浓度变化趋势大致相同，均表现为：10cm＞20cm＞30cm，两种处理土壤CH4和N2O浓度基本随土层深度的增加而增加。. 对于稻-油轮作农田，覆膜和非覆膜处理CH4和N2O的排放都集中在各作物的生长前期，水稻季CH4和油菜季N2O的排放通量均具有较明显的季节变化；全年CH4的排放通量介于-0.76~1.90 mg•m-2h-1，N2O的排放通量介于-44.12~1720.14 μg•m-2h-1。地膜覆盖显著提高了CH4和N2O排放总量，其中覆膜处理全年CH4排放总量为25.21 kg•hm-2，相比常规处理20.93 kg•hm-2高20.5%；覆膜处理N2O的年排放总量为13.10 kg•hm-2，较常规处理下11.20 kg•hm-2的年排放总量提高了17.0%。在100a时间尺度上，覆膜处理下全年排放的CH4和N2O所引起的综合GWP为3948.82 kg CO2•hm-2，较常规处理3039.18 kg CO2•hm-2提高了29.9%，差异显著，表明覆膜不是一种有效的碳减排措施。