Observation Study Of Carbon Exchange Over The Hinterland Of Taklimakan Desert, China

In order to analyze the environmental drivers of soil respiration in an extreme arid desert ecosystem, we measured diurnal variation in winter and autumn soil respiration at Tazhong, a hinterland of Taklimakan Desert in northwest China. Regression analysis was performed with SPSS 21.0. The main conclusions included,(1) Diurnal variation in winter and autumn soil respiration all showed a single peak. The single peak of winter soil respiration appeared at 12:00 noon(local time), after which soil respiration began to decrease, reaching a minimum value at around 4:00 a.m. However, the latter appeared at 11:00, a minimum value at around 20:00 p.m.(2) Although two observation tests were shorter, and based on the two typical observing session of soil respiration rate in its test results, we hypothesize that desert soil respiration had a seasonal pattern, characterized by high in the fall and winter low.(3) Soil temperature at 0cm, modeled by linear equations in proper sequence, was able to explain 86.3% and 62.4% of the diurnal variation in winter and autumn soil respiration, demonstrating that this process is more sensitive to temperature at 0cm than at any other soil layer(10cm, 20 cm, 40cm).(4) Soil respiration exhibited a positive linear correlation with soil moisture at 5cm depth. When linear regression analysis was used to model the relationship between these variables, the fitted linear model explained 69.5% of the diurnal variation in winter soil respiration, demonstrating that, in the extreme arid desert ecosystem, this shallow layer of moisture exerts a large effect on soil respiration. However, the fitted linear model only explained 35.3% of the autumn soil respiration.(5) The greatest contributors to soil respiration were soil temperature at 0cm, followed by soil moisture at 5cm depth.(6) Multiple regression analyses showed that a multi-variable model of soil temperature and soil moisture explained 86.9% and 85.0% of the diurnal variation in winter and autumn soil respiration respectively, which is not significantly better than a single-variable model.(7) For winter soil respiration, the daily average rate of CO2 absorption was –1.45 mg CO2/(m2·h). However, for autumn soil respiration, the daily average rate of CO2 absorption was –3.04 mg CO2/(m2·h).Meanwhile, we also conducted winter and fall surface layer(≤6m) atmospheric CO2 profiles data collected in the same period, and a synchronous meteorological data, analyzed the variation characteristics of surface layer atmospheric CO2 concentration and other meteorological factors on its characteristic effects. The conclusions included,(1) Variation of surface layer CO2 concentration took on single peak curve and the mean CO2 concentration of daytime was higher than night.(2) The daily variation of CO2 concentration ranged from 371.6 to 387.1μmol/mol in winter, while the latter ranged from 395.0 to 413.9μmol/mol.(3) Based on the two typical observing session of surface layer CO2 concentration in its test results, we hypothesize that surface layer CO2 concentration had a seasonal pattern, characterized by high in autumn and winter low.(4) Surface layer CO2 concentration had good response to soil respiration and also showed significant positive correlation with air temperature.(5) The wind speed was notable to CO2 concentration at 1m above surface layer, but relatively not at 0.5m level above surface layer.(6) Surface layer CO2 concentration were jointly controlled by soil respiration and weak meteorological conditions over the hinterland of Taklimakan Desert.