Dynamic Characteristics Of CO₂ And Water Vapor Fluxes And Research On Influence Factors For Hanfu Apple Orchard

In order to promote the study of CO₂ flux and water vapor flux change in orchard ecosystem,the prediction model of CO₂ and water vapor fluxes and the water use efficiency's change rule,the eddy covariance technique was conducted using the“Hanfu”apple orchard.Based on the data of CO₂ and water vapor fluxes from 2017-2018,the energy closure of the apple orchard,the change low of CO₂ flux,water vapor flux and water use efficiency in different time scales,main factors affecting CO₂flux and water vapor flux in daily scale,water use efficiency response to soil moisture content,net radiation,vapor pressure deficit and leaf area index were all explored.The main results were as follows:?1?The diurnal variation of CO₂ flux was"single-valley".In the whole growth period,the action intensity of carbon sink in each month was July>June>August>September>October>April>November.The average value of CO₂ flux in 2017-2018 was-0.103 to0.094mg/?m²·s?and-0.134 to 0.059mg/?m²·s?,respectively.The time of conversion from carbon source to carbon sink in each month was mainly at 5:00 to 7:00,and the time of conversion from carbon sink to carbon source was at 14:30 to17:00.The minimum value of CO₂flux was appeared at 9:00 to 12:00,and the minimum range was-0.671 to-0.038mg/m²·s)and-0.731 to-0.148mg/?m²·s?,respectively.In Daily scale,CO₂ flux was negatively correlated with net radiation,air CO₂ concentration,5cm soil temperature and vapor pressure deficit,positively correlated with atmospheric temperature.The change of CO₂flux during the whole growth period was"double valley",the valley values were appeared in early-June and-0.731 to-0.148mg/?m²·s?,the peak value was appeared in early-August,and the first time valley value was lower than the second valley value,obviously.Apple orchard in Shenyang had stronger carbon sequestration ability than conventional crops.The average daily CO₂flux in 2017 was-0.124mg/?m²·s?,maximum CO₂flux uptake rate was-0.93mg/?m²·s?.The maximum C absorption rate was-31.9g/?m²·d?,total carbon sequestration during the whole growth period was 2.388kg/?m²·a?.The average daily CO₂flux in 2018 was-0.153mg/?m²·s?,maximum CO₂flux absorption rate was-1.48mg/?m²·s?,maximum C absorption rate was-26.94g/?m²·d?,total carbon sequestration during the whole growth period was 2.871kg/?m²·a?.?2?The diurnal variation of water vapor flux was"single peak".The evapotranspiration was larger in June to August.The average range of water vapor flux in two years was basically the same and the range was 0.006 to 0.038g/?m²·s?and 0.005 to 0.039g/?m²·s?,respectively.Water vapor fluxes generally increased between 5:30-7:00,and the maximum occurred mainly at around 11:00 to 13:00.Between 18:00 and 21:00,the decrease stopped and tended to stabilize,and the time to stop was somewhat changed with the month.On a daily scale,water vapor flux was positively correlated with net radiation,10cm soil temperature and wind speed,and negatively correlated with 5cm soil temperature and 30cm soil temperature.The water vapor flux of apple orchard in the whole growth period was"single peak",the peak value generally appeared in the middle of August,and the variation law was in accordance with the"pseudoparabola"function"y=a+bx+ce^dx".The error of evapotranspiration of apple orchard calculated thought eddy covariance method and water balance method was 15%.Thought eddy covariance method,the evapotranspiration of apple orchard in two years was 493.936mm and 510.842mm,the transpiration of apple trees was281.505mm and 340.351mm,the average daily transpiration was 1.280mm/d and 1.568mm/d,separately.?3?The daily instantaneous water use efficiency fluctuated greatly,but the trend was"single peak",and the peak value often appeared at 8:00 to 10:00 per day.The order of water use efficiency in each month was August>September>July>October>June>May.The water use efficiency fluctuated greatly during the whole growth period,too.The whole change trend was"sinusoidal function".The first growth stage was from the beginning to the middle of May,the first decrease from the middle of May to the middle of August,and the second growth stage from the middle of August to the end of the experiment.Using eddy covariance method to calculate the mean values of water use efficiency in two years was 6.369 g/kg and6.864g/kg.During the whole growth period,WUE increased with net radiation,air temperature and VPD,decreased with Air CO₂ concentration.