为给牛角瓜的优质栽培和田间管理提供依据，用LI-6400型光合测定仪于2014年5月观测了元江干热河谷不同牛角瓜叶位叶片光合特性的日变化特征，对牛角瓜不同叶位叶片光合能力进行了研究。结果表明：牛角瓜上下叶位叶片光合速率呈双峰曲线，中叶位呈单峰曲线，上叶位叶片有光合“午休”现象，气孔导度与净光合速率日变化趋势基本一致。各叶位叶片的净光合速率、蒸腾速率、气孔导度、气孔限制值日变化由高到低依次均为上叶位、中叶位、下叶位；胞间CO2浓度呈相反趋势，由高到低依次为下叶位、中叶位、上叶位。研究发现，牛角瓜不同叶位全天最大净光合速率值出现在9：00～10：00，光合“午休”主要是由于叶肉细胞羧化能力下降引起的；除光照因素外，气孔导度是影响光合速率的主要因子。%In order to provide a basis for high-quality cultivation andifeld management ofCalotropis gigantea, diurnal variation of leaf photosynthetic characteristics at differentC. gigantea leaf positions were observed and determined by using portable LI-6400 photosynthesis system in may 2014 at dry-hot valley areas of Yuanjiang, and leaf photosynthetic ability at different C. gigantea leaf positions were researched. The results showed that the curves of diurnal variation of net photosynthetic rate (Pn) of leaves at upper and lower leaf positions had double peaks, and that at mid-position had single peak. The leaves at upper leaf position had the midday depression of photosynthesis. The trend of diurnal variation of Stomatal conductance was consistent with that of net photosynthetic rate. All of the orders of leaf positions based on diurnal variations of net photosynthetic rate, transpiration rate, stomatal conductance and stomatal limited value from high to low, were the upper leaf positions, the mid-position, the lower leaf positions. Inter cellular CO2 concentration showed a contrary trend, and the order was the lower leaf positions, the mid-position, the upper leaf positions from high to low. The results indicated that the maximum values of net photosynthetic rate (Pn) at different leaf positions appeared at 9:00-10:00, and the midday depression was mainly due to decreasing carboxylic ability of mesophyll cells; In addition to the illumination factor, stomatal conductance was the main factor affecting the rate of photosynthesis.
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