| It is becoming a hotspot to research the vegetation restoration and rehabilitation in limestone zone. This paper was experimented on two typical shrubs, Cajanus cajan(L) Millspaugh ,a nitrogen-fixing shrub, and Mahonia fortunei, a non-fixing, shrub. There are four reasons for me to select the two materials to conduct my experiment. First, it is necessary to choose appropriate species to restore and rebuild vegetation in limestone districts; second, it is an important precondition for selection and utilization of the appropriate species to research the photosynthetic physiological characteristics; third, nitrogen-fixing species has important ecological significance in vegetation restoration in limestone districts; last, Cajanus cajan(L) Millspaugh and Mahonia fortunei have much value and take a key role in vegetation restoration and rehabilitation in limestone districts. So, the photosynthetic physiological characteristics of the two species were studied and net photosynthetic rate, transpiration rate , chlorophyll and leaf N content so on were obtained and the difference between the two different species were analyzed so that these results could provide some theoretical advice on how to restore vegetation in limestone districts. The results were as following:(1) The diurnal variation of net photosynthetic rate of Cajanus cajan(L) Millspaugh and Mahonia fortunei were "twin-peaked" curve and appeared "photosynthetic depressed" in the noon that related to non-stomatal restriction factors. The diurnal average net photosynthetic rate of Cajanus cajan(L) Millspaugh was 3.498 μmol·m-2·s-1, higher than that of Mahonia fortunei, which was 2.015 μmol·m-2·s-1.(2) There were different in the seasonal variations of net photosynthetic rate of Cajanus cajan(L) Millspaugh and Mahonia fortunei. The seasonal variation of net photosyntheticrate of Cajanus cajan(L) Millspaugh were "single-peaked" curve and was highest in July ,that is 10.9 μmol·m-2s-1, lowest in October ,that is 2.58 μmol·m-2·s-1 .However, the seasonal variation of net photosynthetic rate of Mahonia fortunei was "twin-peaked" curve, one peak appeared in July and another in October with the highest value of 6.9 μmol·m-2·s-1 and 6.7 μmol·m-2·s-1 respectively. During the six month we experimented, the average net photosynthetic rate of Cajanus cajan(L) Millspaugh was 5.754 μmol·m-2·s-1 and that of Mahonia fortunei was 4.766 μmol·m-2·s-1.We thought the difference of the two kinds of curve of seasonal variation was caused by the leaf structure and physiological biochemical characteristics.(3) The diurnal variations of water use efficiency of Cajanus cajan(L) Millspaugh and Mahonia fortunei were like "L" basically . The average water use efficiency of Cajanus cajan(L) Millspaugh was higher than that of Mahonia fortunei, which was a kind of plant with low photosynthetic rate and low transpiration rate. And the seasonal variations of water use efficiency of the two plants were like "W", with the seasonal average value was 11.473 mmol·mol-1 and 5.500 mmol·mol-1.On the whole, the water use efficiency of Mahonia fortunei was higher than of Cajanus cajan(L) Millspaugh. However, on the day of experiment in summer, the water use efficiency of Cajanus cajan(L) Millspaugh was higher than that of Mahonia fortunei . The possible reason was that the water use efficiency of Mahonia fortunei was effected more than that of Cajanus cajan(L) Millspaugh in summer, which could also be seen in the mild curve of Cajanus cajan(L) Millspaugh.(4) The total chlorophyll, chlorophyll a, chlorophyll b, chlorophyll a/b and carotenoid content of Cajanus cajan(L) Millspaugh were all higher than that of Mahonia fortunei, which was consistent with the fact that the photosynthetic capacity of Cajanus cajan(L) Millspaugh was higher than that of Mahonia fortunei. The seasonal average leaf N content of per gram of Cajanus cajan(L) Millspaugh was 35.62mg,and that of Mahonia fortunei, 14.55 mg, with the former 144.7% higher than the later. As a result, the leaf N content of the two shrubs were positively related with the variation of net photosynthetic rate.(5) The response curve of Pn to light indicated that saturated light intensity of Cajanus cajan(L) Millspaugh was 1 766μmol·m-2·s-1, and light compensation point was 158μmol·m-2·s-1.Comparatively, the saturated light point of Mahonia fortunei was 1 825μmol·m-2·s-1, and the light compensation point was 54μmol·m-2·s-1. It was obvious that the two shrubs were both light-like plants, but the range of light utilized by Mahonia fortunei was wider than that by Cajanus cajan(L) Millspaugh, which indicated that Mahonia fortunei could use weak light and resisted strong light better.
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