| Eddy covariance method (referred to as EC) is a micro-meteorological measurement methods, which has currently become the advanced and preferred method for flux observation in land-atmosphere exchange studies. In the study, we use EC method conventional micro-meteorological systems and plant physiological ecology observation to investigate water vapor exchanges process、variations of NEE and relationship with meteorological factors;in dune and meadow land surface of Horqin Sandy land. And assessment applicability of the carbon、water cycle studies in the area,the main conclusions are as follows:(1) The diurnal variation of latent heat flux over meadow and dune were significantly difference, greater in spring and autumn., respectively 26.2%、30.5%, August is the annual maximum affected by precipitation and surface energy distribution difference; sensible heat flux more consistent seasonal variation, there are obvious differences in the thermal negative conversion time:during the day in April coincided with the largest sand dunes, meadows, respectively 199 W/m2,225 W/m2. From winter to summer, H is positive continue to extend the length of time the negative gradually shortened the length of time. Evaporation of meadow and dune was negatively correlated with precipitation, the rain daily ET values were respectively 14%、40% lower than the sunny of meadow and dune, sandy daily evaporation regular changed with wind speed fluctuations in sunny day,while the high wind speed was unfavorable for meadow.(2) Meadow ecosystem NEE in annual performance carbon sequestration>release. April to September,with enhancement of photosynthesis, the system turned carbon source to carbon sink, in July the carbon peak value is225.08g C/m, October to December when plants into wither period,the system mainly as carbon sinks. Average monthly cumulative carbon emissions is 24.5g C/m2. Net ecosystem carbon exchange (NEE) were controlled by Photosynthetically active radiation(PAR) and leaf area index(LAI) and NEE significantly inhibited by high VPD values during vegetation growing seasons.;Daytime net CO2 exchange had some inhibition in brief heavy rainfall, while sustained low intensity rainfall has stimulating effects on soil respiration at night; Nighttime respiration rate ecosystem Reco increased exponential with an increase of soil temperature Ts.(3) During the whole study period, net radiation captured by the meadow in the form of latent flux and sensible fluxes and soil flux. Among them, the latent and sensible part of energy were routed to surface was 80%,while soil flux routed small part; The degree of coupling approached 1 at beginning of growing season, tends to 0 in exuberant period, which shows latent heat flux between the two system appeared bad couping degree, water vapor flux exchange process was mainly controlled by environments factors in early days of growing period.(4) The characteristics of seasonal variation of ecological water use efficiency perfomed obviously, the value in spring was higher than autumn. The daily average value was 2.01 gC/kgH2O in vegetation season and peak value was 17.45 gC/kgH2O appeared in May. The correlation between the different values of WUE with different environment factors, but had close relationship with NEE. VPD and PAR were mainly environmental factors which controlled the seasonal changes of WUE, and other factors influenced WUE were distinctive in different seasons. |
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