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Lanzhou University (2022)

Research on CO2 Exchange for Different Ecosystems and Its Influence Factors in the Badain Jaran Desert

杨萍

Titre : Research on CO2 Exchange for Different Ecosystems and Its Influence Factors in the Badain Jaran Desert

Auteur : 杨萍

Grade : Doctoral Dissertation 2022

Université : Lanzhou University

Résumé partiel
Arid and semi-arid areas are important parts of terrestrial ecosystem and play a very important role in the carbon cycle of terrestrial ecosystem.The Badain Jaran Desert(BJD)is located in the arid area of northwest China,which has three typical underlying surfaces:lakes,sand hills and grassland.Due to harsh natural conditions and backward transportation and communication,the CO2 budget balance in the BJD is not clear,and the mechanism of carbon cycle is also lacking.Based on this,lake,desert and grassland ecosystems in the Badain Jaran desert ecosystem were studied,and used the eddy covariance(EC)technique to conduct long-term monitoring of CO2 flux of the three ecosystems.The variation characteristics of CO2 flux at different time scales were analyzed.The carbon absorption capacity of the ecosystem was quantified and the nature of its source and sink was clarified.The responses of net CO2 exchange(NEE)in desert and grassland ecosystem to precipitation events of different intensities were analyzed.The main environmental factors affecting CO2 fluxes at different time scales were clarified.The main conclusions are as follows :(1)During the observation period,the carbon sequestration capacity of the lake ecosystem was the weakest,and the annual CO2 flux was-97.07 g C m-2a-1.The average annual NEE of desert ecosystem was-127.54 g C m-2a-1.Grassland ecosystem had the highest carbon sequestration capacity,with an annual NEE of-138.21 g C m-2a-1.According to the carbon sink rate and area of the three ecosystems,it is estimated that the annual carbon uptake in the whole BJD is about 6.652×10 6 t.(2)The temporal variation characteristics of CO2 flux in different ecosystems are different.CO2 uptake in the lake ecosystem mainly occurred from 00:00 to 19:30.The diurnal and diurnal variations of NEE in desert and grassland ecosystems were u-shaped,with CO2 absorbed during the day and released at night.The lake ecosystem has obvious CO2 release phenomenon in summer,and the maximum CO2 uptake in autumn.The amount of CO2 absorbed by desert ecosystem was the highest in summer,and CO2was released in winter.Under the influence of drought,grassland ecosystem will change from carbon sink to carbon source in the growing season.(3)Abiotic factors are the primary reason that the lake ecosystem acts as an atmospheric CO2 sink.Inorganic processes are the main mechanisms controlling the CO2 absorption and releases in the lake,which is dominated by p H and driven by temperature to regulate CO2 exchanges at the interface between lake and air.(4)The threshold value of the NEE response to precipitation was~1.4 mm,indicating that desert ecosystem is extremely sensitive to precipitation events.The higher the precipitation intensity,the stronger the carbon fixation ability,the longer the time to reach the maximum CO2 absorption and the duration of the residual effect.In the context of the warm and humid climate in Northwest China,total precipitation and the frequency of extreme precipitation are expected to increase ;thus,the carbon sequestration capacity of the desert ecosystem will be enhanced

Mots clés : Badain Jaran Desert ;Eddy covariance technique ;Net ecosystem CO2 exchange ;Carbon sink ;Precipitation;

Présentation (CNKI)

Page publiée le 16 octobre 2022