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UBC Theses and Dissertations

Ecophysiology of the effect of red to far-red light ratio on selected weed and crop species Ma, Li


Plants growing in canopies are exposed to reduced light intensity as well as low red/far-red light ratios, a signal of impending competition. In order to advance our understanding of the eco-physiological role of red/far-red ratio in agroecosystems, growth chamber and greenhouse studies were conducted to investigate 1. the growth and morphological responses of common lamb’s-quarters (Chenopodium album L.), redroot pigweed (Amaranthus retroflexus L.) and tomato (Solanum lycopersicum L.) to different red/far-red ratios, 2. how leaf optical properties at red (660 nm) and far-red (730 nm) wavelengths change with leaf position and plant development, and 3. if red/far-red ratio influences response of corn (Zea mays L.), lettuce (Lactuca sativa L.), and pigweed plants to UV-B radiation. Three red/far-red ratios were achieved by using supplemental far-red lamps in growth chambers, while maintaining the photosynthetically active radiation. Results showed that red/far-red ratio treatment influenced several growth and allometric parameters and tomato, lamb’s-quarters, and pigweed differed in this regard. This differential response among species suggests that fluctuations in the red/far-red ratio in canopies could impact inter-plant interactions among these species. Red/far-red ratio in a plant canopy is affected by leaf optical properties. A study of leaf optical properties of lamb’s-quarters, pigweed and tomato using a CI-710 Miniature Leaf Spectrometer showed that leaf optical properties changed with leaf position and plant development, which could modify the light environment in canopies comprising populations of these species. Interestingly, these species differed in this regard, suggesting differences in their ability to signal potential competition. Leaf optical properties, as well as leaf position and plant development effects, therefore, should be taken into consideration in assessing the eco-physiological functions of a vegetation cover. Effect of pre-exposure to low red/far-red ratio on plant susceptibility to UV-B radiation could impact plant interaction. However, my research showed that red/far-red ratio pre-treatment and the associated change in anthocyanin concentration did not alter the response of corn, lettuce and pigweed seedlings to enhanced UV-B radiation. This improves our understanding of the eco-physiological role of these environmental stressors in agro-ecosystems, where both red/far-red ratio and UV-B levels fluctuate.

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