Ultraviolet-B radiation and plant competition: experimental approaches and underlying mechanisms.

Under realistic stratospheric ozone depletion scenarios, ultraviolet-B radiation (280-320 nm) (UV-B) influences plant morphology and plant competitive interactions. Influence of UV-B on plant competition can be studied using a variety of experimental and analytical approaches including inverse yield-density models and allometric, neighborhood or size-structure analyses that provide links between plant and ecosystem responses. These approaches differ in their abilities to extract information regarding competitive interactions and their morphological underpinnings. Only a limited number of studies have been carried out to investigate UV-B effects on plant competition, and most of these have used the replacement series approach, which has received much criticism. Nonetheless, results to date indicate that slight differences in UV-B-induced morphological responses of species grown within associations can alter canopy structure thereby influencing photosynthetically active radiation (PAR) interception and relative competitive ability. Because the response of individuals of the same species is expected to be uniform, UV-B may influence intraspecific competition less than interspecific competition. Before we can make clear generalizations and predictions concerning the effects of this radiation on plant competition, an understanding is crucial of the mechanisms underlying UV-B-induced shifts in competitive interactions by assessing competition over time.