Photosynthetic gas exchange and leaflet movement of Robinia pseudoacacia in relation to changing light environments

On the sunny days, there were little diurnal changes in both azimuth mid directional angle, for either sun- or shade-leaflet. However, there existed a significant diurnal change in midrib angle that reflected movements regarding evasion of light stress around noon hours. On the cloudy day, a very little diurnal difference was found in azimuth, directional and midrib angle. It is suggested that changing light environment is the main factor for inducing leaflet movement of Robinia pseudoacacia, and the rhythmical movement does not attribute to the leaflet movement. Leaf orientation control test showed that the photosynthetic rate (Pn), stomatal conductance (g(s)) and transpiration (Tr) of the artificial Fixed-leaflets were significantly lower than that of control-leaflets. And the leaf temperature (Tl) of the fixed leaflets significantly exceeded that of control-leaflets, which may attribute to the significant difference of light interception between the fixed and control-leaflets. The light-dependent leaflet movement is the morphological adjustment of maintaining optimal physiological status.