遮荫和土壤水分对毛红椿幼苗光合特性的影响

The Effects of Shading and Soil Water Content on Photosynthesis of Toona ciliata var.pubescens Seedlings

采用3种遮荫(全光照、60%遮荫、80%遮荫)和3种土壤水分(高、中和低)处理,研究了毛红椿幼苗叶片净光合速率(Pn)、气孔导度(Co)、胞间CO2浓度(Ci)和叶绿素含量及叶面积等特性。结果表明:毛红椿净光合速率日进程曲线呈“双峰”型,高峰值出现在10:00和16:00,全光照和中度遮荫(60%)情况下有较明显的光合“午休”现象,而强度遮荫(80%)光合“午休”现象不明显。全光照下胞间CO2浓度日进程基本与净光合速率相反,当土壤含水量高时光合作用能力最强。气孔导度日变化呈下降趋势,胞间CO2浓度变化平缓,表明上午10:00以后净光合速率降低主要受非气孔限制因素的影响。在遮荫条件下,毛红椿苗木通过增大叶面积、提高叶绿素含量有效地利用较弱的光辐射,形成适应遮荫条件的生态生存对策。

Net photosynthetic rate （Pn）, stomatal conductance （Co）, internal CO2 concentration （Ci）, chlorophyll content and leaf area were measured in leaves of Toona ciliata var. pubescens seedlings grown in pots with various shading and various soil water contents. The results showed as follows： The diurnal variations of Pn were ＂twin-peaked＂ curve, and the peak value occurred at 10：00 and 16：00 or so. There was an obvious ＂midday depression＂ phenomenon under full light and middle shading （60%）, while it didn＇t occur obviously under strong shading （800//00）. The diurnal variations of Ci were just opposite to Pn under the full light. Photosynthesis was the strongest when water content in soil was sufficient. The decreasing of Cond and even variation of Ci showed that the decreasing of Pn was related to non-stomatal restriction factors after 10：00. With the increase of leaf area and chlorophyll content under shading, the leaves of T. ciliata var. pubescens had the higher utilization efficiency on weak light. The results suggested that the control of soil water content and irradiance might help to promote the growth of T. ciliala var. pubescens.