摘要:华北平原作为典型的冬小麦-夏玉米轮作高水肥精细管理农田，高水高肥管理下其碳排放量高于秸秆还田的固碳量，其生态系统正在以每年77 g（C）·m-2·a-1的速度损失碳。华北平原农田>400 kg（N）·hm-2·a-1的过高氮素投入是造成其碳排放增加的主要原因，其土壤N2O排放强度在氮肥施入量为136 kg（N）·hm-2·a-1时最低，且在施氮量为317 kg（N）·hm-2·a-1时可获得最高作物产量。华北平原土壤中温室气体的产生和消耗主要发生在0~90 cm土壤剖面内，>90 cm土层主要作为土壤包气带中的缓冲层而存在。当前降低华北平原农田温室气体排放除了合理施肥和灌溉，还需要改变固有的农作制度，实行减免耕等保护性措施，并将减排和固碳同步进行。对华北平原温室气体净排放研究，今后需在以下几个方面加强：1）在地-气之间加强冠层尺度温室气体的原位连续在线监测研究，并将稳定性同位素技术应用到此研究中以达到追踪其来源和比例构成的目的。2）在土壤包气带中，利用稳定性同位素技术探索土壤空气中温室气体的来源比例，探索剖面土壤温室气体产生和消耗对土壤-大气界面温室气体排放的响应机制。3）将模型研究应用于土壤-大气连续体温室气体排放研究。
Abstract:The winter-wheat and summer-maize double cropping system in the North China Plain (NCP) is the classic intensive crop production pattern with high water demand and nitrogen fertilizer inputs. The carbon (C) emission quantities are higher than the carbon sequestration quantities in the cropping system. C was being lost from the intensive wheat-maize double cropping system in the NCP at a rate of 77 g(C)·m-2·a-1 when harvest removals are considered, even though crop residue C is input into the soil since 30 years ago. High nitrogen (N) fertilizer application rate[>400 g(N)·hm-2·a-1] results in the increase of C emissions directly. Yield-scaled N2O emission is lowest at N application rate of 136 g(N)·hm-2·a-1. And it is found that maximal crop yield is achieved at a N application rate of 317 g(N)·hm-2·a-1, which is 20% less than current practice. More than 90% of the annual cumulative greenhouse gas (GHG) fluxes originated at soil depths shallower than 90 cm. The subsoil (>90 cm) is not a major source or sink of GHG, but it acts as a 'reservoir'. Considering the synthetic greenhouse effect, some measures of greenhouse gas reductions were put forward in papers such as reductions of fertilizer input and water supply and improving farming system (tillage reduction or zero tillage). Furthermore C reduction needs to be in step with C sequestration. In the future, studies on greenhouse gas emissions in NCP require to be further strengthened in the following aspects:1) in-situ continuous online monitoring of canopy scale greenhouse gases, and using stable isotope techniques to track their sources and proportions; 2) in soil profile, using stable isotope techniques to study the sources and proportions of greenhouse gases, and exploring the responding mechanism between greenhouse gas production/consumption in soil profile and their emissions at soil surface is fairly crucial; 3) using models to estimate greenhouse gas emissions of soil-atmosphere continuum.
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