用Li-6400XT便携式光合作用仪对一年生和当年生濒危植物长序榆幼苗的光合日变化进行了观测,为科学保护提供理论依据和技术途径.结果发现,一年生和当年生长序榆幼苗的光合日变化均为单峰曲线,无"午休"现象.当年生的平均净光合累积量(5.64 μmol·m-2·s-1)大于一年生的净光合累计量(5.05 μmol·m-2·s-1).胞间二氧化碳(Ci)浓度与光合日变化基本上是相反的.气孔导度(Gs)和蒸腾速率(Tr)没有明显的变化规律.光能利用率(LUE)中午12:00最低,水分利用率(WUE)13:00最高.一年生和当年生的光饱和点(LSP)分别为1620.75μmol·m-2·s-1和1123.07μmol·m-2·s-1,二者的光补偿点(LCP)均较低,分别为8.33 μmol·m-2·s-1和8.89 μmol·m-2·s-1,即长序榆幼苗是一光适应幅度较大的植物.偏相关分析表明光合有效辐射(PAR)和大气温度(Ta)是决定其净光合速率的主要环境因子.%Diurnal variations of endangered plant one year and current year Ulmus elongata seedlings were studied by using Li6400XT portable photosynthesis system with the aim of protecting and providing technical approaches. It was found that both current and one year growth Ulmus elongata seedlings had one single peak, which had no "midday depression". For current year seedlings, the average net photosynthetic accumulation (5.64 μmol·m-2·s-1) was greater than the accumulation of net photosynthesis (5.05 μmol·m-2·s-1) of one year seedlings. The diurnal variations of intercellular CO2 concentration (Ci) was opposite to the net photosynthesis. The diurnal variations of stomatal conductance (Gs) and transpiration rate (Tr) had no significant certain law. Light use efficiency (LUE) were lowest at 12:00, water use efficiency (WUE) were highest at 13:00. Light saturation point (LSP) of one year seedlings was 1 620.75 μmol·m-2·s-1, and 1 123.07 μmol·m-2·s-1 for current year seedlings, the light compensation point (LCP)of both were very low, 8.33 μmol·m-2·s-1 and 8.89 μmol·m-2·s-1, respectively. It indicated that Ulmus elongata seedlings would be adapted to a large scale of light. Partial correlation analysis showed that the major environmental factors of net photosynthetic rates were the photosynthetic active radiation (PAR) and air temperature (Ta).
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