干热河谷牛角瓜光合特性

Photosynthesis Characteristics of Calotropis gigantea L. in Dry-Hot Valley

为明确干热河谷典型植被的光合适应机制,以2年生牛角瓜(Calotropis gigantea L.)为材料,采用LI-6400便携式光合作用系统,测定牛角瓜的光合日进程及光合响应曲线。经测定,牛角瓜在雨季光合能力强于旱季,光能利用率(LU,E)雨季高于旱季,而水分利用率(WU,E)则相反;净光合速率(Pn)与环境因子存在一定关系,与光合有效辐射(PA,R)相关性极显著,相关系数为0.949,回归方程为Pn=100.804-0.722RH-1.618Ta+0.017PA,R-0.094Ca;净光合速率、气孔导度(Gs)、蒸腾速率(Tr)呈先升高后降低趋势,胞间CO2摩尔分数(Ci)呈先降后升趋势,气孔限制值(Ls)出现3个升高值,牛角瓜不存在光合午休现象。可见,牛角瓜为典型阳性植物,气温不是直接限制牛角瓜叶片净光合速率的因素,牛角瓜对高温、高光照具有较强的耐性,而不能充分利用热能和光能。

With two-years-old Calotropis gigantea the experiment was conducted to clarify the photosynthetic adaptation mecha- nisms of typical dry-hot valley vegetation and determine diurnal photosynthesis and photosynthetic response curve by LI- 6400 portable photosynthesis system. The leaf photosynthetic ability and light use efficiency （Lu,E ） of C. gigantea are higher in the rainy season than in the dry season. But water use efficiency （ Wu,E） has the opposite trend. Net photosyn- thetic rate （Pn） has the relationship with environmental factors and significant relationship with photosynthetic radiation （ PA,R ） with the correlation coefficient of 0.949 and the regression equation of Pn = 100. 804-0.722RH-1. 618T. ＋0.017PA,R -0.094C,. Net photosynthetic rate, stomatal conductance （ Gs ） and transpiration rate （ Tr） show a single peak curve. Intercellular CO2 content shows a ＂decreased-increased＂ trend. Stomatal limitation value shows three elevated values. Thus, there is no midday depression of photosynthesis in Calotropis gigantea leaves. Therefore, C. gigantea is a typical positive plant. Temperature is not directly limited Pn of the leaf. C. gigantea has stronger resistance to high temperature and stronger illumination, but it can not make full use of heat and solar energy.