The Interaction of Ultraviolet-B Radiation Stress and Plant Competition in Agricultural Plant Populations

The effect of ultraviolet-B radiation enhancement upon the competitive interactions of two species pairs was studied in the field. Wheat (Triticum aestivum L. \u27Bannock\u27) was paired with wild oat (Avena fatua L.) and jointed goatgrass (Aegilops cylindrica Host) to represent competition between species pairs in agricultural situations. Specially modulated ultraviolet lamp systems provided either low ultraviolet-B enhancement (simulation of a 16 % ozone layer reduction based upon the generalized plant action spectrum), high ultraviolet-B enhancement (40 % ozone reduction) or control (ambient solar ultraviolet-B) irradiance. Ultraviolet-B radiation enhancement significantly altered the competitive interactions of the species pairs. However, ultraviolet-B enhancement did not affect total shoot biomass production 1n the mixtures or shoot biomass production of the species 1n monoculture. The direction 1n which competitive interactions were altered appeared to be dependent upon the time at which the seeds were planted. Also, water stress affected some aspects of the interaction between ultraviolet-B enhancement and plant competition but the manner of this effect was inconsistent. Reproductive effort of the species was generally not affected by ultraviolet-B enhancement, except in wild oat plants under interspecific competition