Abstract: Taking the one-year seedlings of Ulmus crassifolia as subjects, which were introduced from America and cultivated in the field, the daily courses of its net production rate (Pn), transpiration rate (Tr) and water utilization efficiency (WUE) in leaves, and its influencing factors were studied under natural condition.The results showed that the curve of Pn diurnal variation was a single peak and its peak value appeared at 11:00;Tr daily courses of leaves from different parts were obviously one-peak curves.Tr peak values of both middle and bottom leaves appeared at 13:00 and peak value of top leaves came out at 15:00 and the descending order of Tr peak values was middle leaves, bottom leaves, top leaves;WUE daily courses of leaves from different parts all presented a one-peaked curve decreasing at one side, WUE of middle and bottom leaves lower than those of top leaves.By main component analysis, path coefficient analysis, or multiple return analysis, major physiological and ecological factors affecting Pn were temperature, Vpdl and light intensity;the influencing factors of Tr and WUE were temperature and Vpdl.

Key words: Ulmus crassifolia, photosynthesis, daily variation, influencing factor

摘要： 以引自美国的南方岩榆1年生大田苗为研究对象,测定叶片净光合速率(Pn)、蒸腾速率(Tr)、水分利用效率(WUE)等日变化及其与生理生态因子的关系。结果表明,不同部位叶片的Pn日变化均呈单峰曲线,峰值出现在11:00,影响Pn的主要生理生态因子为叶面水气压亏缺(Vpdl)、温度和光强;不同部位叶片的Tr日变化均呈明显的单峰曲线,中部叶和基部叶峰值出现在13:00,顶部叶峰值出现在15:00,且中部叶> 基部叶> 顶部叶;不同部位叶片的WUE日变化均呈单边下降的单峰曲线,中部叶和基部叶均低于顶部叶;影响榆树Tr和WUE的主要生理生态因子均是温度和Vpdl。

关键词: 南方岩榆, 光合作用, 日变化, 影响因子