华北平原是我国典型的小麦（C3）/玉米（C4）轮作两熟高产农田区。研究这一区域农田系统呼吸过程中碳同位素的分馏效应对探索农田碳循环生态过程的微观机理具有重要价值。本项目以华北平原小麦（C3）/玉米（C4）两熟农田为研究对象，利用涡度相关系统与13CO2同位素廓线系统，原位观测农田生态系统呼吸通量（FR）及其碳同位素特征（δR）；将LiCor LI 8100土壤呼吸测定系统与静态箱-质谱仪法相结合观测土壤呼吸 (FRs)和土壤异养呼吸通量（FR,hs）及其碳同位素特征。重点研究小麦（C3）/玉米（C4）两熟农田呼吸通量及其碳同位素特征的昼夜、季节和年际变化，阐明农田呼吸构成及其在土壤-大气界面的碳同位素分馏效应；研究农田呼吸及其碳同位素特征与土壤剖面水分、温度及有机质δ13C含量的关系，探索非生物因素对C3（小麦）和C4(玉米)作物呼吸过程中碳同位素分馏效应的影响机制。

Huabei Plain is the typical high-yield area of a winter wheat-summer maize double cropping rotation. The study of the carbon isotope fractionation effect in respiration has fundamental value in probing the microcosmic mechanism of ecological process of agriculture carbon cycle. This study is carried out in wheat (C3) - maize (C4) double cropping rotation in Huabei Plain. The ecosystem respiration (FR) and its carbon isotope signature (δR) are measured in situ by using an eddy covariance system and a CO2 isotope analyzer system, respectively. Soil respiration (FRs), soil heterotrophic respiration (FR,sh) and their carbon isotope signatures (δR) are measured by LI 8100 automated soil CO2 flux system and static chamber-mass spectrometry technique , respectively. The research focuses on the interannual, seasonal, and diel variability in the carbon isotope composition of respiration in a C3/C4 agricultural ecosystem; it clarifies the carbon isotope fractionation effect during respiration at soil-atmosphere interface. The research is devoted to the influences of soil moisture, temperature and δ13C content of soil organic matter on ecosystem respiration and its carbon isotope signature; the object of the research is to find the mechanism of the effects of abiotic factors on the carbon isotope fractionation effect during respiration process in a winter wheat-summer maize double cropping rotation in Huabei Plain.