| Energy Plant Functional Groups (Energy PFGs) is a kind of functional classification method based on plant energy properties. Though photosynthesis of plant, sun energy was transformed to chemical energy and stored in plants, would different Energy PFGs show different photosynthetic characters? In order to explore the relationship between the both, the leaf photosynthetic parameters of Leymus chinensis,Cleistogenes squarrosa,Potentilla acaulis and so on, including the diurnal variations of net photosynthetic rate (Pn), Stomatal conductance (Sc), Transpiration rate (Tr) were measured using a LI-6400 Portable Photosynthesis System in Typical Steppe of Xilingol from the end of July to mid August. Diurnal variations of photosynthesis of different Energy PFGs and their's representative plant was compared. The result showed that the diurnal variation of Pn of all the plants took on "double-peak" curve with remarkable midday depression. The peaks generally appear at 12 and 16 o'clock. During 12 to 14 o'clock, there is a phenomenon called "sleep at noon",which refers to that plants stop their process of photosynthesis. When comparing the major tendency of the curve, the Pn of high-energy PFGs is lower than low-energy PFGs's., the same pattern happens in Sc and Tr. This phenomenon may be explained by vigorous life activities and reproduction strategy of low-energy PFGs.Moisture is a significant factor of affecting plant photosynthesis. As the representive of high-energy PFGs in typical steppe, chinensis's rate of photosynthesis increased with the increase of moisture, they have a outstanding fitted relationship. And under the condition of increasing moisture, the net rate of photosynthesis of chinensis in the degradation sample are higher than these in the fencing sample,the net rate of photosynthesis of chinensis lossing PFGs are higher than these keeping PFGs, which are related to the competition between the composition of one PFG and between PFGs.
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