中文摘要：

在自然条件下,利用Li-6400光合仪测定疏叶骆驼刺（Alhagi sparsifolia Shap.）和多枝柽柳（Tamarix ramosissima Ledeb.）7-9月份的气体交换参数,分析2种植物净光合速率（Pn）与环境因子——光合有效辐射（PAR）、空气温度（Ta）、大气CO2浓度（Ca）、相对湿度（RH）之间的关系,以明确影响其光合作用的主导环境因子,为恢复和重建过渡带植被提供理论依据。结果显示：（1）疏叶骆驼刺不同时期Pn的日变化均为单峰曲线,多枝柽柳7、8月份的Pn日变化为单峰曲线,9月份为双峰曲线,且疏叶骆驼刺Pn的平均值（7.08μmol·m-2·s-1）高于多枝柽柳（5.54μmol·m-2·s-1）。（2）2种植物7-9月份的蒸腾速率（Tr）日变化均为单峰曲线,且疏叶骆驼刺Tr的平均值（5.46mmol·m^-2·s^-1）高于多枝柽柳（4.40mmol·m^-2·s^-1）;疏叶骆驼刺和多枝柽柳的胞间CO2浓度（Ci）的日变化趋势均呈＂倒钟型＂曲线,与Pn日变化趋势相反。（3）2种植物7-9月份的WUE日变化进程与各自的Pn日变化规律基本一致,多枝柽柳的WUE日均值（1.21 mmol·mol^-1）明显高于疏叶骆驼刺（0.97mmol·mol-1）。（4）偏相关分析显示,骆驼刺和柽柳的Pn与PAR呈显著正相关关系,而与RH呈显著负相关关系;回归分析显示,骆驼刺和柽柳Pn日变化的变异分别有35.6%和42.4%是由环境因子的日变化造成的;通径分析显示,各环境因子对Pn都具有显著的影响,其大小顺序分别为：Ta〉RH〉PAR〉Ca（骆驼刺）和PAR〉Ca〉Ta〉RH（柽柳）,且骆驼刺在7-9月份内PAR均为决策变量,RH为限制变量（除7月份外）;而柽柳在8、9月份内PAR均是决策变量,RH、Ca是限制变量。研究表明,疏叶骆驼刺属于高光合高蒸腾低水分利用效率型,多枝柽柳属于低蒸腾低光合高水分利用效率型;7月份骆驼刺和柽柳Pn的下降主要是由于气孔限制引起,而8、9月份主要是由非气孔因素限制所致;PAR和RH是影响骆?

英文摘要：

To clear the main factor affecting photosynthesis and provide a theoretical basis for the restitution and restoration vegetation in transition zone, we determined gas exchange parameters of Alhagi sparsifolia and Tamarix ramosissima by the Li-6400 （LICOR,USA） under natural conditions from July to September, analyzed the relationship between photosynthesis and environmental factors, such as photosynthetically active radiation （PAR） ,air temperature （Ta） ,air CO2 concentration （Ca） ,air relative humidity （RH）. The results show that： （1）The diurnal change pattern of Pn of A. sparsifolia is one-humped curve from July to September,while it could be expressed as a two-humped curve on July and September. The mean values of Pn were 7.08 μmol·m^-2·s^-1 and 5.54 μmol· m^-2 ·s^-1. （2）The curves of diurnal variation in Tr had one peak,the mean values of Tr were 5.46 mmol· m^-2 ·s^-1 and 4.40 mmol · m^-2·s^-1. They all exhibited an inverted bell-shaped variance in the diurnal change of Ca from July to September. （3）The diurnal change of WUE liked Po ,the mean value of WUE were 1.21 mmol· mol^-1 and 0.97 mmol · mol^-1 ,respectively. （4） Pn and PAR were positively correlated （P〈0.01）, negatively associated with R H （P〈0. 01） on partial correlation analysis; the diurnal changes of Pn in A. sparsifolia and T. ramosissima were 35.6%, 42.4 respectively,which were caused by the diurnal variance of environmental factors on regression analysis; Each environmental factor has remarkable influence to Pn on path analysis, Ta〉RH〉PAR〉Co （A. sparsi- folia） and PAR〉Ca〉 Ta〉RH （T. ramosissima）. Importantly,the decision variable of A. sparsi folia was PAR, and RH was the limitation variable except for July;while PAR was only the decision variable on July and September,both RH and Ca were decision variables. These analyses indicated that A. sparsifolia had high photosynthetic rate,high transpiration rate and low water use efficiency in comparison with T. ramo- sissi