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Measuring the Short-Term Plant Photosynthetic Response to Varying Light Quality Using Light Emitting Diodes (Leds)

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Measuring the Short-Term Plant Photosynthetic Response to Varying Light Quality Using Light Emitting Diodes (Leds) Measuring the Short-term Plant Photosynthetic Response to Varying Light Quality Using Light Emitting Diodes (LEDs) Michael A. Schwalb Department of Bioresource Engineering McGill University Montreal, Quebec, Canada A thesis submitted to McGill University in partial fulfillment of the requirements of the degree of Master of Science December, 2013 © Michael Schwalb, 2013 1 Abstract Light emitting diodes (LEDs) emit narrow bandwidth light and have the potential to increase the spectral efficiency of supplemental lighting in greenhouses by optimizing spectral output for plant growth and yields. At the moment of writing, data describing the plant response to varying light quality and quantity was limited. The objective of this research was to examine photosynthetic response of plants to varying light quality and quantity and to gather photosynthetic response data that could be used to design an optimal spectrum for a prototype LED array for plant growth experiments. The action spectrum of tomato (Solanum lycopersicum), lettuce (Lactuca sativa) and petunia (Petunia × hybrida) seedlings was measured at three irradiances (30, 60 and 120 µmol m-2 sec-1) using LED arrays with peak wavelengths from 405nm – 700nm and a bandwidth of 25nm (full width at half maximum). The action spectrums for all plant species at all three irradiances were characterized by localized blue and red action peaks within the range of 430 to 449 nm and 624 to 660 nm respectively. A peak also occurred at 595 nm for 30 µmol m-2 sec-1.The photosynthetic response of tomato, lettuce and petunia to varying red (660nm) and blue (430nm) wavelengths with and without background broadband radiation was also measured. For all three species tested, with and without background radiation, the optimum photosynthesis range occurred within the red to blue ratio (r:b) range of 5:1- 15:1 except for petunia without background radiation for which the maximum occurred at 50:1. These results suggest that the optimal red to blue ratio for photosynthetic activity for tomato, lettuce and petunia occurred between a red to blue ratio of 5:1-15:1. 2 Résumé Les diodes électroluminescentes (DEL) émettent une lumière relativement monochromatique et pourraient accroître l’efficacité des lampes pour les serres commerciales en émettant des longueurs d’ondes optimisées pour le rendement des plantes. L’objectif de ce projet a consisté à examiner l’effet des longueurs d’ondes sur l’activité photosynthétique des plantes. L’activité photosynthétique des tomates (Solanum lycopersicum), laitues (Lactuca sativa) et pétunias (Petunia × hybrida) a été mesurée à trois puissances d’irradiation (30, 60 and 120 µmol m-2 sec-1) en utilisant des DELs avec une émission maximale entre 405 nm et 700 nm et une bande passante de 25 nm. La réponse photosynthétique maximale à chaque niveau d’irradiation se situait dans la portion bleu et rouge du spectre visible, soit respectivement entre 430 - 449 nm et 624 to 660 nm. Un maximum a aussi été observé à 595 nm à 30 µmol m-2 sec-1. L’effet de la proportion des longueurs d’onde bleue et rouge (émises par les DELs) sur l’activité photosynthétique des tomates, laitues et pétunias a aussi été mesuré avec et sans le rayonnement de fond. Pour chaque espèce, avec et sans le rayonnement de fond, la proportion optimale (en terme de rouge et bleu) pour l’activité photosynthétique se situait entre of 5:1- 15:1, sauf dans le cas du pétunia, pour lequel le maximum se situait à 50:1 sans rayonnement de fond. La proportion optimale pour l’activité photosynthétique a diminué avec le rayonnement de fond pour chaque espèce à chaque niveau d’irradiation. 3 Authorship and Manuscript This thesis is written in a manuscript based format. The contribution of authors are as follows: (1) M. Schwalb – design of optimized light treatments for photosynthetic data collection, design and operation of experiments, as well as data collection, compilation, analysis and interpretation; (2) Dr. Lefsrud-provided guidance on experimental design, supervised experiments and reviewed thesis; (3) Tahera Naznin- helped develop methodology of experiments and helped collect and analyze photosynthetic data (4)- Julie Gagne- provided technical expertise with experimental instruments and helped collect and analyze data (5) Blake Bissonette- provided technical expertise with the operation and maintenance of experimental instrumentation. 4 Acknowledgements I would like to thank my supervisor Dr. Lefsrud for providing generous support and invaluable guidance. I would also like to thank all of the co-authors for their technical expertise which made this project possible as well as the MITACS Accelerate program and General Electric Lighting Solutions for providing funding and facilitating a great experience as an intern in a corporate setting. This project would also not have been possible without the love and support of my wife Jaime, my dad, my mom and my sister. Finally, I would like to thank Pablo Gucciardo for his technical assistance with drafting a figure for the experimental setup. 5 Table of Contents Abstract ........................................................................................................................................... 2 Résumé............................................................................................................................................ 3 Authorship and Manuscript ............................................................................................................ 4 Acknowledgements ......................................................................................................................... 5 Table of Contents ............................................................................................................................ 6 List of Figures ................................................................................................................................ 10 List of Tables ................................................................................................................................. 11 List of Equations ............................................................................................................................ 12 1. General Introduction................................................................................................................. 13 1.1. Thesis Motivation .............................................................................................................. 13 1.2. Research Problem ............................................................................................................. 14 1.3. Objectives .......................................................................................................................... 15 1.4. Hypothesis ......................................................................................................................... 15 Abbreviations ................................................................................................................................ 16 2. Literature Review ...................................................................................................................... 17 2.1. Availability of Solar Irradiance .......................................................................................... 17 2.2. Current Supplemental Lighting ......................................................................................... 17 2.3. Light Emitting Diode Lighting ............................................................................................ 19 2.4. LED Efficiency and Cost Evolution with Time .................................................................... 21 2.5. Benefits of LEDs for Plant Growth ..................................................................................... 22 2.6. Photosynthetic Reaction ................................................................................................... 24 2.7. Pigments ............................................................................................................................ 26 2.8. Photosynthetically Active Radiation ................................................................................. 29 2.9. Plant Response to Varying Light Quantity ........................................................................ 29 2.10. Light Quantification ......................................................................................................... 31 2.11. Action Spectrum .............................................................................................................. 31 2.12. Action Spectrum Measurements .................................................................................... 32 2.13. Photosynthetic Response to Varying Light Quality ......................................................... 34 6 2.14. Plant Selection for Experimentation ............................................................................... 37 2.14.1. Tomato Greenhouse Crop Profile ........................................................................... 37 2.14.2. Lettuce Greenhouse Crop Profile ............................................................................ 38 2.14.3. Petunia Greenhouse Crop Profile ........................................................................... 38 References .................................................................................................................................... 40 Connecting Statement to Chapter 3 ............................................................................................
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