| As an important part of terrestrial ecosystems,desert ecosystems have a certain impact on the global climate change due to the exchange and transmission of water,heat and CO2.Therefore,it is of great significance to study the changes and control mechanisms of carbon and water cycles for the entire terrestrial ecosystem.In this paper,the research object of selection of two typical horqin sand dunes and meadow ecosystem,the eddy covariance and ecological-weather-soil environmental monitoring technology,and discusses the typical ecosystem hydrothermal carbon flux variation characteristics and the influence of environmental factors on its role,deeply analyze the ecological system of heat and water transfer regularity and characteristics of carbon cycle and the main conclusions are as follows:(1)The diurnal variation of net ecosystem exchange(NEE)between dune and meadow is u-shaped.The maximum daily CO2 absorption flux of dune and meadow appeared in July.The CO2 fluxes of dune and meadow have obvious seasonal variation,which increases first and then decreases.In the growing season,the total NEE of dune is-453.60 g·m-2·d-1,and the total NEE of meadow is-1307.42 g·m-2·d-1,both of which are carbon sinks,but the meadow ecosystem has a strong carbon sink capacity.The main factors affecting dune and meadow NEE are photosynthetically active radiation(PAR)and temperature(T).(2)The monthly mean daily variation of hydrothermal flux in dune and meadow ecosystems is unimodal.The meadow ecosystem in the growing season was dominated by the exchange of latent heat flux.The maximum daily flux appeared in July(323.22 W·m-2),and the maximum sensible heat flux of dune appeared in July(62.70 W·m-2).By comparing the energy budget of the two underlying surfaces,it is found that the net radiation of dune is mainly distributed to sensible heat flux,while that of meadow is mainly distributed to latent heat flux,indicating that there is a great difference in energy distribution between different underlying surfaces.The correlation analysis showed that the latent heat flux of dune and meadow in the growing season was significantly correlated with net radiation and air temperature,and the sensible heat flux was significantly correlated with net radiation.The sensible heat flux of dune is significantly correlated with the relative humidity of air,while meadow is significantly correlated with the latent heat flux of air.In the growing season of 2018,the total evapotranspiration of dune(May to October)and meadow(June to October)was 233.72 mm and 424.79 mm respectively.In the growing season,net radiation has the greatest influence on evapotranspiration of dune and meadow ecosystems,followed by temperature.In the June to mid-to late September of the meadow,evapotranspiration and air relative humidity have an obvious negative correlation.(3)In daytime,the carbon flux and evapotranspiration of the net ecosystem of dune and meadow showed a relatively consistent trend,while the CO2 flux and evapotranspiration at night did not fluctuate at a small value.The fitting slope of carbon-water flux in each typical day of dune is:June 20>July 14>August 10>September 8.The fitting slope of the carbon-water flux in each typical day of the meadow is:July 14>June 20>August 10>September 8.The carbon and water fluxes in each typical day of dune and meadow ecosystems show a characteristic of significant positive correlation,and the higher the slope is,the higher the Water use efficiency will be.The carbon and water fluxes of dune and meadow in each month were also positively correlated linearly.In the growing season,dune water use efficiency is generally lower than that of meadow land,which is closely related to the arid and sparse vegetation habitats of dune.It shows that it is very important for desert ecosystems to improve the efficient utilization of regional water resources. |
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