UV-B Radiation, Photomorphogenesis and Plant-Plant Interactions

Abstract

Ultraviolet-B radiation comprises a relatively small amount of the solar spectrum at the earth's surface, yet radiation in this waveband can induce avariety ofgrowth andmorphologicalresponsesin higherplants. Although the precise photosensory mechanisms responsible for these morphological responses have yet to be fully elucidated, it does appear that some of these responses represent specific photomorphogenic effects of UV-B, while others are the result ofmore general stress responses to UV-B. The degree to which these specific and non-specific mechanisms contribute to the overallmorphologicalresponses to UV-Binfield-grown plantshas received little attention. While the majority of studies to date have focused on the potential responses to elevated UV-B that would occur with stratospheric ozone depletion, it is clear from a number of recent studies that current levels of solar UV-B, even in regions experiencing minimal stratospheric ozone depletion, can influence plant morphology. Thus, solar UV-B is presently an important abiotic factor influencing plant growth. The morphologicalalterationsinduced byambientorrealistic UV-Benhancements, however, are typically subtle and may be of minor consequence for the overall performance and success of isolated plants. These alterations have the potential to be ecologically important in highly productive, crowded environments where subtle differences in morphology and leaf placement in canopies can be magnified by competitive interactions for light. The extent to which asymmetric competition for light further amplifies size differenceswill likelybe determined bythe degree to which plant morphology is affected by the changes in UV-B, UV-A, PAR and R:FR that occur within plant canopies.