摘 要 ：用LCA4型便携式全自动光合测定仪，在自然条件下，于7月下旬的晴朗天气测定了群落冠层和林下两种不同光环境下夏蜡梅(Sinocalycanthus chinensis)的净光合速率（Pn）、胞间CO2浓度(Ci)、呼吸速率（Rd）、气孔阻力（rs）的日进程，并与其伴生植物悬铃叶苎麻(Boehmeria platanifolia)、盐肤木(Rhus chinensis)、水马桑(Weigela japonica var. sinica)的光合日进程相比较。结果表明：夏蜡梅冠层的光合速率日进程呈“双峰”曲线，有明显的“午休”现象，经分析其“午休”的原因主要是由非气孔因素引起的；林下夏蜡梅则表现为“单峰”曲线，净光合速率较低，最大净光合速率不及冠层的1/2，相关分析结果表明其最重要的影响因子是光合有效辐射（p=0.001）；与其它伴生植物相比，夏蜡梅的日均光合速率、最大光合速率、水分利用效率和光合速率/呼吸速率都明显偏低,在群落竞争中处于不利地位。
Abstract:The photosynthetic parameters of Sinocalycanthus chinensis in both overstory and understory, including the diurnal changes of net photosynthetic rate (Pn), intercellular CO2 concentration (Ci), dark respiration rate (Rd) and stomatal resistance (rs), were measured using a LCA4 Portable Photosynthesis System. The photosynthetic parameters of the accompanying plants such as Boehmeria platanifolia, Rhus chinensis and Weigela japonica var. sinica were also measured for comparison. The results showed that the diurnal changes of photosynthesis of S. chinensis in the overstory took on “double-peak” curve with remarkable midday depression. The midday depression was mainly due to non-stomatal limitations. On the contrary, the diurnal changes of photosynthesis of S. chinensis in the understory took on “one-peak” curve with low Pn. The maximal Pn was only half of that of S. chinensis in the overstory. The correlation analysis showed that the limiting factor for this low Pn might be light intensity (p=0.001). Compared with its accompanying plants, S. chinensis was in a disadvantaged status in the community with low photosynthetic capacity, water use efficiency, and the ratio of photosynthetic rate to respiration rate.