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中文摘要：
以吐鲁沟国家森林公园内百年左右树龄的祁连圆柏为对象,采用Li-6400光合作用测定系统,在自然环境条件下测定了其生长季内各月份生理生态因子和净光合速率的日变化,探讨祁连圆柏生理生态特征以及与其生理生态因子间的关系.结果表明,在整个生长季内,祁连圆柏的净光合速率日变化为双峰型曲线,其在10：00和16：00达到峰值,于14：00达到最小值,光合作用存在明显的午休现象＂,而月份之间的净光合速率表现为8月〉5月〉6月〉7月.祁连圆柏的气孔限制值与净光合速率有相似的日进程,呈现出M＂型的双峰曲线,分别在10：00和16：00达到峰值,而胞间CO2浓度日变化趋势与气孔限制值相反,表现出W＂型双峰曲线.水分利用效率与净光合速率有相同的日变化趋势,其在整个生长季内表现为5月〉8月〉7月〉6月.在整个生长季内,影响祁连圆柏光合变化的主要决定生理生态因子是胞间CO2浓度和气温,限制生理生态因子是气孔导度和光合有效辐射强度.
英文摘要：
Temperature is the most important factor affecting growth at high altitudes.As tree use much of the allocate carbon gained from photosynthesis to produce branches and stems,information on the diurnal course of photosynthesis and the physiological characteristics is very crucial to assessing temperature thresholds for Qilian juniper.From May 2010 to August 2010,diurnal variations of photosynthesis of Qilian juniper and variations changes between different months in growing season were studied by Li-6400 portable photosynthetic system under natural condition.The result showed that the curve of diurnal variation in net photosynthetic rate（Pn） for Qilian juniper has a double peak,at which the Pn reaches the peak value at 10：00 and 16：00 and reach the minimum value at 14：00.And this indicates that there existed ＂midday depression＂ in the photosynthesis of Qilian juniper.The diurnal variation trend of stomatal conductance and water use efficiency were similar with that of Pn.Throughout the growing season,Pn between the different months showed the following variation：August〉May〉June〉July.The main physiological factor affecting the characteristics of Pn of Qilian juniper was intercellular CO2 concentration（Ci） and the main ecological factor was air temperature（Ta）,photosynthetic active radiation（PAR） was the limiting factor.This study suggests that temperature plays a very important role in the growth of Qilian juniper.
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