Research On CO₂, Water And Heat Fluxes Of Tamarix Shrubs In The Lower Reaches Of Tarim River

Research on CO₂, water and heat fluxes in terrestrial ecosystem is a hot and difficult issue, playing akey role in the understanding of ecosystem change, predicting the trend of global climate change andevaluating the carbon sequestration of ecosystem. Scholars have put forward various researches andshowed that the fluxes of different ecological ecosystems under the assumption of homogeneous underlyingsurface can be calculated by the eddy covariance method, and also, this method was significant forrestoring the degraded ecosystem.The desert ecosystem has faced a serious threat to the ecological balance in the recent years. In orderto reflect the response of the global and regional climate change and importance of energy balance fordesert ecosystems. This study took the lower reaches of Tarim River as target area, and observed the wholegrowing season of the Tamarix shrubs by the eddy covariance method. Combined with the synchronousmeteorological data, this study discussed the characteristics of microclimate in the extreme arid region, theresults show that, The diurnal variation of microclimate in the lower reaches of Tarim River had significantvariation. The soil temperature at2cm layer and6cm layer in different shrubs were obvious sinusoid. Therange of soil temperature reduced with the depth of underlying surface in desert ecosystem. Monthlyvariation of net radiation and photosynthetically active radiation were gradually decreased, which weremainly caused by the water vapour in the atmosphere and air muddy degree. There was obvious diurnalchange of surface radiation balance, and the peak time were inconsistent between the shortwave radiationand long-wave radiation. Due to the special nature of the study area, the surface temperature enhanced thedependence of solar radiation. The CO₂and water and heat fluxes of Tamarix shrubs in the desert riparianforest had obvious variation with the changes of weather, monthly variation and day alternates with night.The most of energy from Tamarix shrubs were used to the latent heat flux in desert riparian, sensible heatexchange was less, accounted for75.5%and8.4%of the net radiation respectively. There were greatdifferences between the distribution of the energy conversion and balance degree under different weatherconditions. The diurnal variation of surface energy flux and energy allocation trend was appearedsingle–peak quadratic curve. Rn and LE were the important energy income and expenditure terms ofTamarix shrubs. It was found that energy balance residuals were appeared systematic diurnal cyclealternating with negative and positive value. There was a significant difference in conversion of energyallocation and energy balance under different weather condition. During the observation period, thereexisted energy closure phenomenon of Tamarix shrubs. The effective energy was less than turbulent energy,the energy closure ratio was72.3%, and was81%at daytime, whereas only19%at nighttime. The energyclosure was better in sunny day than cloudy, rainy and sandy day, and better in the daytime then nighttime.There was a significant change in the energy balance ratio before the sunrise and after the sunset. Byeffecting of photosynthesis, the magnitude of energy balance closure and changes of carbon flux had closerelations to the air temperature and moisture degree under the different weather condition. These resultshave suggested that the underestimation of carbon flux was the main reason of the imbalance of energybalance.