中文摘要：

以一年生盆栽新疆野苹果实生苗为试材，研究了经3种水分梯度处理后第20天苹果叶片净光合速率（Pn）和水分利用率（WUE）的日变化规律。结果表明，正常水分处理和中度水分胁迫下新疆野苹果Pn日变化为不典型双峰型，且Pn下降主要受气孔因素限制；重度水分胁迫下新疆野苹果Pn日变化为严重午休型，Pn下降主要受非气孔因素限制。方差分析表明，中度和重度水分胁迫使新疆野苹果Pn日均值与对照分别达到显著和极显著差异。3种水分梯度处理后新疆野苹果WUE日变化均呈先快速下降后缓慢上升的趋势，并表现上午时段的WUE大于下午时段；WUE目均值按对照、中度和重度水分胁迫依次降低。相关性分析表明，随着水分胁迫的增强，Ta，Ca，RH等生态因子对新疆野苹果Pn的影响越大，其中RH对Pn的影响最显著。

英文摘要：

The effect of water stress on diurnal changes of photosynthetic and water use efficiency in one- year-old potted Malus sieversii at the 20th day after 3 soil water gradients treatment was investigated. The results were summarized as follows： The daily progress pattern of Malus sieversii Pn was a nontypical double peak pattern under normal water treatment and moderate water stress, and the drop of Malus sieversii Pn was controlled by stomatal factor. The daily progress pattern of Malus sieversii Pn was the serious midday depression pattern under severe water stress,and the drop of Malus sieversii Pn was controlled by non-stomatal factor. The variance analysis showed that mean value of Malus sieversii Pn and the control went up to significant and extremely significant difference respectively under moderate and severe water stress. The daily progress pattern of WUE on Malus sieversii shifted from the rapid decline to the slow upward trend at 3 soil water gradients,and WUE in the morning was higher than that in the afternoon. Water use efficiency on mean value decreased gradually under moderate and severe water stress. Through the correlative analysis between diurnal changes of photosynthetic rate and environmental factors, it was confirmed that the effect of Ta,Ca,RH on Pn become more and more conspicuous with increases in water stress,and RH was the dominant factor.