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研究了在沙漠地区典型的高温低湿条件下，沙冬青的气体交换特征。结果表明：沙冬青叶片具有典型的双峰净光合速率曲线，即在中午表现出气孔关闭并伴随着光合速率的大幅度下降。但中午光合速率下降期间，沙冬青叶片胞间ＣＯ２浓度不但没有下降，反而大幅度增加（９∶００－１０∶００），继而保持相对稳定（１０∶００－２０∶００）。同时气孔导度和气孔限制值也下降，日变化幅度小，且终日低下，这与沙冬青冠层的ＶＰＤ和气温密切相关。我们认为沙冬青净光合速率下降的决定因素是叶肉细胞的光合活性，但沙冬青在中午气孔导度的下降不是造成光合午休的主要原因，而是在沙漠干旱环境中实现水分利用最优的对策。
The gas exchange characteristics of A. sativa under typical conditions of high temperature and low humidity in the desert area were studied. The results showed that A. sativa leaves had a typical double-peak net photosynthetic rate curve, which showed stomatal closure at noon and accompanied with a sharp drop in photosynthetic rate. During the noon photosynthetic rate decline, however, the intercellular CO2 concentration in A. sativa leaf not only did not decrease, but increased sharply (9: 00-10: 00) and then remained relatively stable (10:00-20: 00). At the same time, the stomatal conductance and stomatal limitation also decreased, the diurnal variation range was small, and all day low, which was closely related to VPD and temperature of canopy. In our opinion, the declination factor of net photosynthetic rate of A. sojae is the photosynthetic activity of mesophyll cells. However, the decrease of stomatal conductance of A. sojae at midday is not the main reason of photosynthesis midday break, but the best way to achieve water use in desert and arid environment. .