Short-term impacts of elevated UV-B radiation on soybeans

The impact of increased solar ultraviolet-B (UV-B) exposure due to stratospheric ozone depletion can negatively affect plant growth and physiology, decreasing crop productivity. While some effects of prolonged elevated UV-B exposure on plants is clear, relatively little is known about the short-term effects of UV-B exposure, although, there are evidence of short-term UV-B increases that likely occur during summer. Two greenhouse experiments were conducted to examine the short-term effects of UV-B exposure on stomatal conductance (g,), UV-B absorbing compounds and photosynthetic pigment concentrations of soybean cultivars Glycine max [L.] Merr. cvs. Essex and Williams 82. Results showed that changes in leaf reflectance at 552 and 714 nm with UV exposure appear to be linked to UV-B induced alterations in pigment concentrations and the changes in reflectance seemed to be more dependent on the period of exposure rather than the UV-B dosage received. The UV-B exposed Williams 82 exhibited lower g_s compared to UV-B exposed Essex throughout the experiment. The concentrations of carotenoids, chlorophyll a and total chlorophyll in leaf extracts were unchanged in response to an 18-h UV-B treatment in Essex but they increased significantly in Williams 82. Anthocyanin did not change significantly in either cultivar after the 18-h exposure. The 18-h UV exposure did result in substantially higher of UV-B absorbing compounds in Essex compared to Williams 82. Results of a 6-h UV-B exposure caused an induction of Chlorophyll a/b binding protein (CAB) and Phenyl ammonia lyase (PAL) in the irradiated leaves of Williams 82 and Essex and an up regulation in Chalcone synthase (CHS) in Williams but not in Essex. Further work should assess whether these short-term responses are related to the long-term UV-B mechanisms of damage and protection in soybeans and examine how the induction of genes are related to sensitivity of soybeans to UV-B stress.