Date of Award

5-2013

Degree Type

Thesis

Degree Name

Departmental Honors

Department

Plants, Soils, and Climate

Abstract

Light-emitting diodes (LEDs) are a rapidly developing technology for plant growth lighting and have become a powerful tool for understanding the spectral effects of light on plants. Several studies have shown that some blue light is necessary for normal growth and development, but the effects of blue light appear to be species dependent and may interact with other wavelengths of light as well as photosynthetic photon flux (PPF). Here we report the photobiological effects of three types of white LEDs (warm, neutral and cool) on the growth and development of radish, soybean, and wheat. All species were grown at two PPFs (200 and 500 μmol m-2 s-1) under each LED type, which facilitated testing the effect of absolute (μmol photons m-2 s-1) and relative (percent of total PPF) blue light on plant development. Root and shoot environmental conditions other than light quality were uniformly maintained among six chambers (three lamp types x two PPFs). All LEDs had similar phytochrome photoequilibria and red:far red ratios. Blue light did not affect total dry weight (DW) in any species, but significantly altered plant development. Overall, the low blue light from warm white LEDs increased stem elongation and leaf expansion while the high blue light from cool white LEDs resulted in more compact plants. For radish and soybean, absolute blue light was a better predictor of stem elongation than relative blue light, but relative blue light better predicted leaf area. Absolute blue light better predicted the percent leaf OW in radish and soybean and percent tiller OW in wheat. The largest percentage differences among light sources occurred in low light (200 μmol m-2 s-1) . These results confirm and extend the results of other studies indicating that light quantity and quality interact to determine plant morphology. The optimal amount of blue light likely changes with plant age as plant communities balance the need for rapid leaf expansion, which is necessary to maximize radiation capture, with prevention of excessive stem elongation. A thorough understanding of this interaction is essential to the development of light sources for optimal plant growth and development.

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Faculty Mentor

Bruce Bugbee

Departmental Honors Advisor

Jeanette Norton

Capstone Committee Member

Larry Rupp