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Variation of CO2 flux and its response to environmental factors in a maize agroecosystem in Zhangye irrigation area.

ZHANG Lei1,2,3, SUN Rui1,2,3**, QIAO Chen2, LIU Shao-min1,2, XU Zi-wei1,2, TANG Yao2, HAO Lü-yuan2, ZHANG Rong-hua2   

  1. (1State Key Laboratory of Remote Sensing Science, Jointly Sponsored by Beijing Normal University and the Institute of Remote Sensing Applications, CAS, Beijing 100875, China; 2School of Geography and Remote Sensing Sciences, Beijing Normal University, Beijing 100875, China; 3Beijing Key Laboratory for Remote Sensing of Environment and Digital Cities, Beijing 100875, China)
  • Online:2014-07-10 Published:2014-07-10

Abstract:

CO2 flux was measured continuously in a maize agroecosystem in Zhangye irrigation area during the growing season (June to September) using the eddy covariance technique to study the variation of CO2 flux and its response to key environmental factors. The results showed that there was a distinct diurnal variation of CO2 flux, with CO2 absorption in the daytime and emission at night. The maximum CO2 absorption occurred at filling stage and with a maximum value of -1.426 mg·m-2·s-1. Maize agroecosystem is characterized by carbon absorption during the growing season, and the ability to absorb CO2 is significantly different at different growth stages, which was ordered as filling stage > jointing stage > maturity stage > seedling stage. We also used the MichaelisMenten equation and exponential curve fitting method to analyze the impact of photosynthetically active radiation (PAR) on daytime CO2 flux, and the impact of temperature on the ecosystem respiration at night. The results showed that CO2 absorbing intensity increased with PAR. PAR was the dominant factor to control photosynthesis under low solar radiation, and the carbon assimilation rate increased slowly under high solar radiation. The light quantum efficiency of maize ranged between 0.00098 and 0.0022 mg·μmol-1 during the observing period. The nighttime ecosystem respiration exponentially increased with temperature, and the dominant factor varied with growth stage. Soil temperature was the dominant factor of nighttime ecosystem respiration at the seedling stage, while air temperature was the dominant factor at the other growth stages.
 

Key words: the middle reaches of Heihe River, land use transition, ecological quality, ecological grade