A Research On Carbon Fluxes Of Maize Agroecosystems In Semi-arid Area

Increased CO₂ gas concentrations can lead to problems such as the greenhouse effect and sea level rise,while continued co2 rise could cause more serious ecological problems.Researching the variation of CO₂ content in the atmosphere is of great significance for understanding the global carbon cycle process.Global farmland accounts for 38%of total land area,and agroecosystems make a significant contribution to the global carbon cycle.Therefore,the measurement of carbon fluxes in agroecosystem and their responses to environmental variables are critical to understanding the physiological behavior of agroecosystem and predicting future climate change.Based on the carbon flux,meteorological data,and photosynthetic physiological characteristics of maize agroecosystems,this paper analyzes the response laws between net photosynthetic rate,stomatal conductance and carbon flux of maize to environmental factors,and explores the conversion of individual scale to canopy scale carbon flux in maize agroecosystems The following conclusions are drawn:（1）The daily changes of net photosynthetic rate and stomatal conductance of maize showed obvious photosynthetic"midday depression phenomenon",and the response trend of environmental factors such as temperature,moisture and saturated water vapor pressure difference to net photosynthetic rate and stomatal conductivity was basically the same when the light intensity was fixed.（2）The exponential model and the M-M（Michaelis-Menten）model are suitable for simulating the light and CO₂ response processes of the net photosynthetic rate of maize leaves in this area.The light and CO₂ response parameters fitted by the Ye zi piao model are more accurate,and the model is more suitable than the empirical model for the analysis of the response of stomatal conductance to atmospheric CO₂ concentration in the region,and through the analysis of three stomatal conductivity models,including BB（Ball-Berry）model,BBL（Ball-Berry-Leuning）model and Leuning model,the calculated value of the BB model is closest to the actual measured value.The stomatal conductivity models suitable for the region are in order from good to bad>BBL model>Leuning model.（3）Maize agroecosystems in the region have strong carbon sink capacity during the growing season,Moreover,the CO₂ flux of maize during the growing season showed a"U"shaped curve.The daily mean co2 flux of maize during the growing season varied from-35.18 to-0.23μmol·m^-2·s^-1 range;The order of the main environmental factors that affect CO₂ flux and stomatal conductivity is;the photosynthetic effective radiation>temperature>CO₂ concentration>saturated water vapor pressure difference;in addition,the carbon sink capacity of maize agroecosystems was greatly affected by stomatal conductance,and the CO₂ flux（F_c）and stomatal conductivity（g_s）showed a very significant correlation,and the correlation coefficient reached 0.69.（4）The net photosynthetic rate of maize,leaf area index and carbon flux had the same change trend,and the determination coefficient of CO₂ flux and population net photosynthetic rate（Pn·LAI）reached 0.53,and the correlation rate of the canopy was calculated by using the Leuning model model that introduced CO₂variables,and the results showed that the determination coefficient of the net photosynthetic rate of the crown calculated and the measured CO₂flux reached 0.58,while the determination coefficient of the two before the improvement was only 0.24.That is,the improved calculated canopy net photosynthetic rate can be used to predict the CO₂ flux of maize cropland ecosystems in the Huining area.