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在华北平原冬小麦／夏玉米轮作田采用涡度相关法进行了连续两年的碳通量观测,研究农田生态系统碳通量的构成及其变化特征,并分析碳交换对主要环境因子的响应．结果显示:夜间净碳交换量(NEE)与0～10 cm地温呈明显的指数关系,两年度(2002年11月～2003年10月和2003年11月～2004年10月)的Q10分别为2．94．和2．40．通过模拟计算得到总初级生产力(GPP)和生态系统呼吸(Rec)．冬小麦、夏玉米GPP的光响应曲线均符合直角双曲线方程．玉米季平均最大光合速率(Amax)与表观初始光能利用率(a)大于麦季．冬小麦a值随LAI增加而增大．作物主要生长季农田NEE的日变化明显:白天吸收、夜晚释放CO2．其他月份农田以碳排放为主,NEE的日变化不显著．农田NEE日较差4～5月和8～9月较大,其它月份较小．农田NEE,GPP和Rec呈明显的季节变化．2003年和2004年玉米田最大日平均碳吸收量分别为-10．20和-12．50 gC·m-2·d-1;麦田最大日平均碳吸收量分别为-8．19和-9．50 gC·m-2·d-1．麦田和玉米田的最大碳吸收量分别出现在4～5月和8月中旬,和GPP最大值出现时间一致．冬小麦和夏玉米主要生长季(3～5月和8～9月)的NEE由GPP支配．GPP主要受PAR和LAI影响．温度对GPP的影响在早春较为明显．7月Rec达到全年最大,Rec和GPP对NEE的贡献相当．其余月份NEE以Rec为主,温度成为NEE的主要控制因子．从生长季NEE总量看,两年度的麦季分别为-77．6和-152．2 gC·m-2·a-1,玉米季分别为-120．1和-165．6 gC·m-2·a-1,玉米季均大于麦季．两年度冬小麦／夏玉米轮作田的年均NEE分别为-197．6和-317．9 gC·m-2·a-1,表明华北平原农田是大气CO2的汇．若考虑收获籽粒的碳,则农田由碳汇变为碳源:两年度分别为340．5和107．5 gC·m-2·a-1．受温度、降水等气候因子及施肥、耕作等农田管理措施影响,农田碳交换的年际变化很大．实行免耕和一年一熟制是减少土壤碳排放、增加作物碳吸收的有效途径．
In the North China Plain, winter wheat / summer maize rotation cropland was subjected to two consecutive years of carbon flux observation by using the eddy covariance method to study the composition of carbon flux in farmland ecosystem and its variation characteristics and to analyze the response of carbon exchange to major environmental factors. The results showed that nighttime net carbon exchange (NEE) had a significant exponential relationship with 0 ~ 10 cm ground temperature. The Q10 of the two years (November 2002-October 2003 and November 2003-October 2004) were 2.94. And 2.40. Total primary productivity (GPP) and ecosystem respiration (Rec) were calculated by simulation. The light response curves of winter wheat and summer maize GPP were in accordance with the rectangular hyperbolic equation. The average maximum photosynthetic rate (Amax) and apparent initial energy utilization (a) of maize were greater than that of maize. Winter wheat a value increases with increasing LAI. Daily diurnal changes of farmland NEE in the main crop growing season are obvious: absorption during the day and release of CO2 at night. In other months, farmland is dominated by carbon emissions, while diurnal changes in NEE are not significant. Farmland NEE diurnal difference from April to May and August to September larger, smaller in other months. Farmland NEE, GPP and Rec showed obvious seasonal changes. The maximum daily average carbon uptake of maize fields in 2003 and 2004 was -10.20 and -12.50 gC · m-2 · d-1, respectively. The maximum daily average carbon uptake by maize fields was -8.19 and -9 .50 gC · m-2 · d-1. The maximum carbon uptake by wheat fields and corn fields appeared in April-May and in mid-August, respectively, in agreement with the appearance of maximum GPP. The NEE of winter wheat and summer maize is dominated by GPP in the main growth seasons (March-May and August-September). GPP is mainly affected by PAR and LAI. The effect of temperature on GPP is more pronounced in early spring. Rec the largest in the year in July, Rec and GPP contribution to NEE quite. The remaining months NEE mainly Rec, temperature as the main control factor NEE. According to the total amount of NEE in the growing season, the wheat seasons in the two years were -77.6 and -152.2 gC · m-2 · a-1, and the maize seasons were -120.1 and -165.6 gC · m -2 · a-1, maize season average greater than wheat quarter. The annual average NEE of winter wheat / summer maize rotation was -197.6 and -317.9 gC · m-2 · a-1, respectively, indicating that the North China Plain farmland is the sink of atmospheric CO2. When considering harvesting grain carbon, farmland turns from carbon sinks to carbon sources: 340.5 and 107.5 gC · m -2 · a -1 for the two years, respectively. Affected by temperature, precipitation and other climatic factors as well as farmland management measures such as fertilization and cultivation, the carbon exchange in farmland varies greatly from one year to the next. The implementation of no-tillage and one-year cooked crops is an effective way to reduce soil carbon emissions and increase crop carbon absorption.