Variation of CO2 flux and its response to environmental factors in a maize agroecosystem in Zhangye irrigation area
CO2flux 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 CO2flux and its response to key environmental factors.The results showed that there was a distinct diurnal variation of CO2flux,with CO2absorption 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 CO2flux,and the impact of temperature on the ecosystem respiration at night.The results showed that CO2absorbing 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.