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UBC Theses and Dissertations

Effect of light intensity on size hierarchy of redroot pigweed and transmission of far-red light through leaves of selected species Gaire, Rashmi


In order to investigate the effects of light intensity on (1) growth, morphology, and size hierarchy of Amaranthus retroflexus, and (2) transmission of far-red (FR) light through leaves lambsquarters (Chenopodium album), redroot pigweed (A. retroflexus) and bush beans (Phaseolus vulgaris), field experiments were conducted using a randomized complete block design with five replications per treatment. Plants were grown under four light intensities (22%, 33%, 55% and 100% of full sunlight) using 3, 2, 1 and 0 layers of mesh screen, respectively. These treatments represented approximately 400, 600, 1,000 and 1,800 µE m−² s−¹ light intensity on a clear day at noon at the Totem Field at UBC. Size hierarchy for plant height significantly increased with decreasing light intensity. Size hierarchy at 22% light intensity was 67% higher compared to that at 100% sunlight. Size hierarchy of shoot biomass was not affected by light level. The magnitude of several growth/morphological characters decreased with decreasing light intensity. Since light treatments were applied to relatively uniform populations, effect of light intensity on size hierarchy could possibly be due to genetic variability within a pigweed population. In order to study the effect of light intensity on FR transmission through leaves, plants were subjected to four light intensity treatments as described above. Lambsquarters and bean leaves developed at 22% light intensity transmitted higher FR light, compared to those developed at 100% sunlight. There was a weak negative correlation between specific leaf weight and FR transmission in PW (R² = 0.16) compared to bean (R² = 0.78) and lambsquarters (R² = 0.69) leaves. FR transmission from pigweed leaves was generally higher compared to lambsquarters and bean leaves but there was no consistent and/or significant difference in FR transmission through pigweed leaves developed at different light intensities. The leaf position on plant stem did not influence FR transmission in this study. These results show that light intensity influences FR transmission characteristics of leaves and the three species employed in this study differ in this regard. Leaf optical properties as well as leaf area should therefore be considered while assessing plant-plant interactions in mixed populations.

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