Study on Chlorophyll Fluorescence Kinetics of Three Speices in Genus Dendrobium Cultivated in Greenhouse in the Winter Season

The Dendrobium genus includes some important medicinal and famous ornamental plant species over the world. Some species in this genus demonstrated the characteristics of crassulasean acid mechanism plant. Three species i.e., Dendrobium primulinum, D.nobile and D.chrysotoxum were selected as the experiment objects to study their photosynthesis and growth status in greenhouse during the winter season by means of measuring the gas exchange in combination with determining the chlorophyll fluorescence kinetics. The results showed that D. primulinum exhibited typical traits of CAM plants, when its apparent photosynthetic rate was still minus value before 11:00 am while the electron transport rate was relatively high, which resembled the stage III tendency of diurnal fluctuation of CAM plants. With low apparent photosynthetic rate, D.nobile and D.chrysotoxum were adaptive to shade environment with weaker solar radiation. Comparatively speaking, D.chrysotoxum manifested more typical C3 plant characteristics. The 16℃ temperature in the early morning posed a chilling stress to D.primulinum to certain extent, meanwhile D.nobile and D.chrysotoxum were not negatively effected, showing that the later two species were more adaptive to low temperature.