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 depressi...