中文摘要：

在我国河西走廊中部沙漠区，选择20年生以上C4荒漠植物梭梭（Haloxylon ammodendron）和沙拐枣（Calligonum mongolicum）植株，分干旱环境、雨后近地层空气湿润和人工树下挖坑浇水补充土壤水等3种水分条件，比较研究它们的光合作用特征。结果表明，在干旱环境下，梭梭和沙拐枣均表现出不同程度的强光下光合速率（Pn）下降现象，光系统Ⅱ光化学效率（Fv／Fm）明显降低，表现为光抑制。但在雨后空气湿润和人工浇水，使空气湿度和土壤湿度提高的条件下，2种植物的Pn日变化呈单峰型，Fv／Fm日变化小，没有光抑制现象。2种植物的Pn日平均值在雨后空气湿润条件下小于浇水后，浇水后第1天的Pn值明显高于第2天。水分条件改善后，梭梭和沙拐枣光合作用的光补偿点降低，光饱和点升高，光合速率对时间的积分加大。研究得出，水分胁迫导致C4荒漠植物梭梭和沙拐枣出现光抑制，提高空气湿度或者土壤湿度，都能避免光抑制，提高光能利用率。

英文摘要：

In order to probe into the responses of photosynthesis of C4 desert species Haloxylon ammodendron and Calligonum mongolicum under different moisture conditions, thus providing a scientific basis for the conservation of desert ecosystem and restoration of damaged regions, the diurnal courses of their net photosynthetic rate （Pn） and photochemical efficiency of PS Ⅱ （ Fv/Fm）, and the responses of Pn to different light intensities under three different water conditions were studied in the desert in the middle section of the Hexi Corridor regions in Gansu Province, China （39°20＇N, 100°08＇E, 1380 m a. s.1. ）. The three water conditions were arid environment （AE）, near-ground moist air condition during post-rain period （PR）, and condition of artificial supplement of soil water （SW）. Adult plants （more than 20-years-old） of H. ammodendron and C. mongolicum, were selected to be studied.The results showed that the diurnal course of Pn of H. ammodendron and C. mongolicum exhibited a non-typical bimodal pattern with a decline under intensive irradiation in the arid environment, but a unimodal pattern under the PR and SW. The diurnal changes in Fv/Fm exhibited an obvious decline under intensive irradiation in the arid environment, but did not under the other two conditions. Those suggested that there existed photoinhibition under the arid environment, but no under higher air humidity and soil moisture content conditions. Both two species performed higher daily mean Pn under PR and SW than that under arid environment. The daily mean Pn for both species one to two days after SW was higher than that one day after the PR. The mean Pn for the first day after SW was obviously higher than that in the second day. Compared to that under the arid environment, the daily mean Pn of H. ammodendron was 3.1μmolCO2·m^-2·s^-2 higher under the PR, and 9.7 （the first day） and 7 μCO2 m-2·s^-1（the second day） higher under the SW, respectively. Once water condition was improved, the light compensat