Light quantity and quality strongly influence plant growth. Solar radiation is one of the main environmental factors driving vegetation carbon assimilation. As one of the natural climatic variables, clouds change the fraction of diffuse radiation arriving on the land surface and can influence carbon dioxide exchange between vegetation and the atmosphere. In this study, CO 2 flux was continuously measured during the vegetative growing season (June鄄August) from 2006 to 2008 by the eddy covariance systems in a mixed plantation in the Xiaolangdi area, Henan province. The clearness index (k t) was used to describe the effects of cloudiness on solar radiation. Clear mornings and afternoons were identified based on the change of k t with solar elevation (茁) at a half鄄day scale. The impacts of cloudiness on the net ecosystem exchange of carbon dioxide (NEE) were investigated to reveal the mechanism of changes in coordinate of solar radiation and other

Energy balance in the terrestrial ecosystem plays an important role in regional climate and water balance. By using the open鄄path eddy covariance and micrometeorological observation systems, turbulent energy fluxes and available energy were measured in a mixed plantation in the Xiaolangdi area in the North China during the growing season of 2012 (May鄄September). The diurnal and monthly variations of energy balance terms were analyzed, and energy closure and Bowen ratio were discussed. The results showed that the diurnal variation of energy balance terms were similar to that of net radiation, and the variation order of energy balance terms was net radiation >latent heat flux >sensible heat flux >soil heat flux. The time of keeping positives for energy balance terms in a day became shorter from May to September as energy balance terms were influenced by sunshine hour. The maximal net radiation occurred in June with a value of 418.5 MJ m-2

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