中文摘要：

采用人工控制土壤水分的方法（称重法），采用Li-6400便携式光合测定系统，对刺槐和侧柏苗木净光合速率、蒸腾速率、气孔导度、胞间CO2浓度及其相应的环境因子进行了测定。结果表明：充分供水条件下，刺槐、侧柏苗木光合速率日变化呈“双峰”型曲线，均有不同程度的光舍“午休”现象，且上午的光合速率明显高于下午。气孔导度受水分和光热胁迫的影响，日变化呈凹型曲线。胞间CO2浓度受空气CO2浓度和气孔导度的双重影响，呈现出早、晚高，正午低的日变化规律。水分利用效率最高值出现在上午较早的时分，且上午的水分利用效率明显高于下午。光能利用效率呈现出早、晚高，正午低的凹形日变化曲线。

英文摘要：

In semi-arid region of Loess Plateau, the net photosynthetic rate, transpiration rate, stomatal conductance, intercellular CO2 concentration of Robinia pseudoacacia and Platycladus orientalis seedlings and proportional factors were measured with the Li-6400 portable photosynthesis system under sufficient soil moisture. The results showed that the diurnal course of net photosynthetic rate displayed a ＂double peak＂ pattern and a typical ＂noon＂ pattern, net photosynthetic rate was higher in forenoon than that in afternoon. Stomatal conductance was affected by the water, light and heat stress, which displayed a hollow pattern. The intercellular CO2 concentration was affected by the atmosphere CO2 concentration and stomatal conductance, which displayed a hollow pattern. The water use efficiency culminated in the early morning, water use efficiency was significantly higher in the morning than that in the afternoon. The energy use efficiency showed low-concave curve. According to Farquhar and Sharkey＇s view, resulting in net photosynthetic rate reasons for the decline in both constraints and non-stomatal pores constraints, the decline of net photosynthetic rate in the morning was mainly caused by the constraints of the pore, the reduce of net photosynthetic rate at noon and afternoon was mainly attributed to the leaf cells to reduce the carboxylation efficiency.