The seasonal variation of CO2 flux in a wheat field of the Loess Plateau
黄土塬区麦田CO2通量季节变化

The seasonal variation of CO2 flux in a winter wheat field of the Loess Plateau was studied using an eddy covariance method. The following results were obtained. (1) Daily CO2 flux was closely related to growing stages, photosynthetically active radiation , and soil temperature. (2) The average daily CO2 flux at different growing stages followed the order of: jointing and booting >reviving >erecting >heading >ripening >grain-filling > seedling and tillering >wintering period. (3) There was little correlation between daytime CO2 flux and photosynthetically active radiation at the seedling-tillering, heading, and maturing stages; but there was weak correlation during grain filling, and strong correlation in the other stages. There was significant correlation between CO2 flux and nighttime soil temperatures at the 2-cm depth at the wintering, heading and jointing and booting stage, and low correlation at the other stages. (4) The wheat field became carbon source after harvest. The carbon budget of a given day was affected by the weather of the day as well as the rainfall condition in the previous day.