Heliotropic leaf movement of Sophora alopecuroides L.: An efficient strategy to optimise photochemical performance

Sophora alopecuroides L. (Leguminosae) is a perennial herbaceous plant that is characterized by resistance to sand burial. It grows mainly in sandy soil in arid desert, grassland edges, and continental river ecosystems. It is a dominant species of herbaceous synusia and major forage grass species in the continental river ecosystems of northwest China. Research focusing on its responses to biotope could improving the understanding of survival strategies of herbaceous plants in arid regions. However, previous studies on S. alopecuroides focused mainly on phytochemistry and phytopharmacology. Only few studies focused on a survival strategy and adaptation mechanism to environmental conditions, especially in the hyperarid desert. 

Thus, researchers studied the survival adaptation strategy of S. alopecuroides L. to habitat conditions in an arid desert riparian ecosystem in the Ejina basin of Inner Mongolia, northwest China. They examined the responses of heliotropic leaf movement to light conditions and their effects on plant photochemical performance.  

S. alopecuroides leaves did not show any observable nyctinastic movement but they presented sensitive diaheliotropic and paraheliotropic leaf movement in the forenoon and at midday. Solar radiation was a major factor inducing leaf movement, in addition, air temperature and vapour pressure deficit could also influence the heliotropic leaf movement in the afternoon. Both diaheliotropic leaf movement in the forenoon and paraheliotropic leaf movement at midday could help maintain higher photochemical efficiency and capability of light utilisation than fixed leaves. Paraheliotropic leaf movement at midday helped plants maintain a potentially higher photosynthetic capability and relieve a risk of photoinhibition. The findings indicated the effective adaptation strategy of S. alopecuroides to high light, high temperature, and dry conditions in arid regions. This strategy can optimise the leaf energy balance and photochemical performance and ensure photosystem II function. 

This study was published in Photosynthetica in June 2015.