云锦杜鹃叶片光合作用日变化特征

自然条件下,对云锦杜鹃光合作用日进程和光响应进行了观测,结果表明:夏季晴天云锦杜鹃阳叶净光合速率日进程曲线为"双峰"型,光合效率午间明显降低.胞间CO2浓度的日进程基本与净光合速率相反,中午胞间CO2浓度增高表明净光合速率午间降低主要受非气孔限制因素的影响.暗呼吸速率日进程呈单峰曲线,中午最高.阴叶净光合速率在一天的大部分时间里变化不大.一天分时段光响应试验表明,阳叶饱和光强和表观量子效率上午较高,下午有所降低,而光补偿点下午有所上升.阴叶的这些光合参数在上午和下午没有明显的变化.这些研究结果表明,强光下光抑制的发生是引起云锦杜鹃阳叶光合效率午间降低的重要原因.逐步多元回归和通径分析表明,光合有效辐射和空气温度是直接影响净光合速率日变化的主要因子.

The diurnal variation of photosynthesis in leaves of Rhododendron fortunei

Diurnal variations of photosynthesis and response to light in the leaves of Rhododendron fortunei were studied under natural conditions. The results indicated that in the typical summer sunny days, the curve of diurnal variation of net photosynthetic rate (Pn) in the sunnyleaves was dual-peaked with obvious midday depression of the photosynthetic efficiency. The diurnal variation of internal CO 2 concentration (C i) was just opposite to Pn. The increase of C i at midday indicated that the midday depression of the photosynthetic efficiency was mainly influenced by the non-stomatal limited elements. The respiration rate (R) was the highest at midday with single-peaked curves of diurnal variation. There was small variation of Pn in the shadeleaves at the most time in a day. The response to light at different time in a day showed that the saturated light intensity and apparent quantum yield (AQY) were higher in the morning and decreased in the afternoon while the light compensation points increased. No matter in the morning or in the afternoon, the variations of these photosynthetic parameters in the shadeleaves were slight. These results indicated that the main reason of the midday depression of the photosynthetic efficiency in the sunnyleaves of Rhododendron fortunei was the photoinhibition caused by strong light. The analysis of stepwise multi-regression and path coefficient showed that the photosynthetically active radiation (PAR) and ambient temperature (T a) were the main direct factors which affected the diurnal variation of Pn.