Abstract: It's indicated that the light saturation point, light compensation point and net photosynthetic rate of three species of Dendrobiums in Huoshan county are all low and they need feeble and scattered lights for their growth. Relative humidity is the main factor affecting photosynthesis and variation of stomatic aperture. Decreased relative humidity induces decreased net photosynthetic rate. When the air temperature is below 20℃ and relative humidity is above 80%, the stomatic aperture varies with light intensity one-peakedly. When the air temperature and relative humidity are above 20℃ and 90%respectively, the variation of aperture has a significant positive correlation with light intensity. At above 20℃ and below 80% of relative humidity, no correlation between them can be found and the diurnal variation of stomatic aperture shows a two-peak changing pattern. The content of chlorophyll b in leaves is slightly higher and there is a higher absorption peak at 430 nm, showing Dendrobium in Huoshan county having the photosynthetic characteristics of shade plant.

Key words: Dendrobium, Photosynthesis, Diurnal variation of stomatic aperture