Title : Leaf optical properties and response of selected weeds and crops to red/far-red light ratio
Plants growing in canopies are exposed to reduced light intensity as well as low red/far-red (R/FR) ratio, which is a signal of impending competition. We studied effects of R/FR ratio on common lambsquarters (Chenopodium album L.), redroot pigweed (Amaranthus retroflexus L.) and tomato (Lycopersicon esculentum), how leaf optical properties for red (660 nm) and far-red (730 nm) wavelengths change with leaf position and plant development, and if pre-exposure to R/FR ratio influences response of corn (Zea mays L.), lettuce, and pigweed plants to UV-B radiation. Different R/FR ratios (0.3, 0.6, and 1.1) were achieved by using supplemental far-red LED lamps in growth chambers, while maintaining the photosynthetically active radiation. Leaf reflectance, transmittance and absorptance at red and far-red wavelengths were measured using a CI-710 Miniature Leaf Spectrometer. Different UV-B radiation treatments were achieved by filtering the radiation from UVB-313 fluorescent tubes using 1 (high UV-B), 2 (medium UV-B) and 3 (low UV-B) layers of cellulose acetate film in a glasshouse. Lamb’s-quarters, pigweed and tomato differed in their response to changes in R/FR ratio. Leaf optical properties, which can affect the R/FR ratio in plant canopies, differed with leaf position, plant development and species. These findings suggest that populations with different proportions of these species may differ in R/FR ratio in their canopies, which could impact plant-plant interactions differently. R/FR ratio pre-treatment and the associated change in anthocyanin concentration did not alter the response of corn, lettuce and pigweed plants to enhanced UV-B radiation.