| By using the eddy covariance technology,we collected the flux and environmental data of the typical Haloxylon ammodendron ecosystem in the Minqin oasis-desert ecotone during the whole year of 2018,and studied the characteristics of the flux source area,carbon flux and water use efficiency（WUE）in the ecosystem,and then analyzed the control mechanism of different environmental factors on the carbon flux and WUE.The results from this study provide the theoritical and application reference for assessing the ecosystem service functions of the oasis-desert ecotone in the arid regions of China and the related research on climate change.The main conclusions are given as follows:（1）The carbon flux observed in Haloxylon ammodendron plantations was generally originated from the target observation area.Of which the flux source area under stable atmospheric stratification is much larger than that under unstable condition.Taking a typical sunny day as an example,the diurnal variation of flux source area is shown as follows:from the morning,turbulent exchange intensifies,atmospheric stratification transits to instability,and the area of source area decreases gradually.After noon,the turbulent exchange weakened,the stratification turned to a stable state,and the flux source area began to increase again.（2）The net ecosystem carbon exchange of Haloxylon ammodendron plantation showed a bimodal curve in the growth season 2018.The total sequestrated carbon was 3.45 g C·m-2 in 2018,which is a weak carbon sink;On a half-hour scale,daytime net ecosystem carbon exchange is mainly affected by photosynthetically active radiation（PAR）and increased with increasing PAR.It was consistent with the Michaelis-Menten rectangular hyperbola change,but when the vapor pressure deficit（VPD）is great than 2.5 k Pa,this increasing trend tented to flat.Nighttime net ecosystem carbon exchange increased with increasing temperature,with the estimated temperature sensitivity of ecosystem respiration（Q10）being 1.7.Regardless of day or night,the net carbon exchange through the whole season was strongly correlated with soil temperature at P-value<0.01.（3）The daily WUE of Haloxylon ammodendron plantation showed a single-peak around16:30 pm in May,June and October of 2018,which increased firstly,reaching a peak of more than 1.09 g C·kg-1H2O,and then quickly decreased.In other months,the curve was flat and at a low level.Seasonal changes of WUE were regulated by precipitation,the WUE of the whole growth season in 2018 was about 0.74 g C·kg-1H2O.The WUE of this plantation was weakly correlated with meteorological factors on the half-hour scale,but the correlation was obviously enhanced on the daily scale.The WUE had a quadratic curve relationship with net radiation（Rn）,air temperature,VPD and wind speed on the daily scale.The WUE gradually increased with the increase of the positive meteorological factors firstly and and began to decrease when reached to a certain threshold.Among meteorological factor,Rn was the dominant factor controlling WUE change.This study reveals the dynamics of contribution area of observed carbon fluxes,carbon flux and water use efficiency and the mechanism of environmental impact of typical Haloxylon ammodendron plantation ecosystem in Minqin oasis-desert ecotone,which providing data support and theoretical basis for scientific management of plantation ecosystem in arid areas of Northwest China and for related research on climate change. |
PDF Full Text Request