Influence of R/FR ratio on response of maize, lettuce, and Amaranthus retroflexus L. to UV‐B radiation

Plant species differ significantly in their response to environmental stressors and exposure to one stressor can modify their susceptibility to another stressor, which can have significant implications for crop‐weed competition. Plants exposed to low red/far‐red light (R/FR) ratio in a canopy may experience enhanced UV‐B radiation at a subsequent growth stage. The low R/FR ratio pre‐exposure may impact the susceptibility of weeds and crops to UV‐B radiation differently. This study investigates if exposure to different R/FR ratios and the associated changes in anthocyanin concentration influence plant susceptibility to subsequent UV‐B radiation. Maize ( Zea mays L.), which contains anthocyanin in the leaf sheath, and lettuce ( Lactuca sativa L.) and Amaranthus retroflexus L. (redroot pigweed), which contain anthocyanin in the lamina, were exposed to 0.3 and 1.1 R/FR ratio in growth chambers. Following R/FR ratio treatments, anthocyanin concentration in leaf sheath (maize) or lamina (lettuce and A. retroflexus ) was measured and plants were exposed to three levels of UV‐B radiation. UV‐B exposure significantly inhibited a variety of plant growth and allometric parameters; however, R/FR ratio pre‐treatment did not influence plant response to subsequent UV‐B exposure. Pre‐exposure to low R/FR ratio reduced anthocyanin concentration by 60% in maize leaf sheath, and 31% and 100% in lettuce and A. retroflexus lamina respectively, but this influence did not affect the plant response to UV‐B radiation. These findings are significant to our understanding of the ecophysiological underpinnings of crops and weeds and their interactions in agroecosystems where both R/FR ratio and UV‐B radiation levels fluctuate.