GROWTH AND MORPHOLOGICAL ACCLIMATION OF SEEDLINGS TO BLUE, GREEN, AND RED LIGHT FROM LIGHT-EMITTING DIODES By Heidi Marie Wollaeger A THESIS Submitted to Michigan State University in partial fulfillment of the requirements for the degree of Horticulture – Master of Science 2013 ABSTRACT GROWTH AND MORPHOLOGICAL ACCLIMATION OF SEEDLINGS TO BLUE, GREEN, AND RED LIGHT FROM LIGHT-EMITTING DIODES By Heidi Marie Wollaeger Several experiments were performed with impatiens, marigold, petunia, salvia, and tomato seedlings to quantify how different ratios of blue (B, peak=446 nm), green (G, peak=516 nm), orange (O, peak=596 nm), red (R, peak=634 nm), and hyper red (HR, peak=664 nm) from light-emitting diodes (LEDs) regulated plant growth while maintaining similar cultural and environmental conditions. Seedlings grown under O, R, and/or HR LEDs with background B and G light developed similar plant growth attributes including leaf size, stem length, and biomass accumulation. Therefore, selection of LEDs for horticultural lighting could be based on other factors such as economics. In another experiment, plants grown under ≥25% B light were 41 to 51% shorter and had 35 to 57% less fresh shoot weight than those grown under only R light at the same total photosynthetic photon flux. In a third experiment, plants grown under as little as ˗2 ˗1 10 μmol∙m ∙s of B light were 23 to 50% shorter, had 37 to 50% less fresh weight, up to 43% thinner leaves, and up to 49% less leaf area than plants grown under only R light. Seedlings under 50% G+50% R light were shorter than plants under only R light but taller than plants under only B light, suggesting that G light stimulated blue-light receptors (e.g., cryptochrome), but to a lesser extent than treatments with B light. Therefore, we postulate that a minimal quantity of B light (and to a lesser extent, G light) stimulates one or more B-light receptors that suppresses leaf and stem extension growth, which subsequently limits photon capture and constrains biomass accumulation of seedlings. ACKNOWLEDGEMENTS I would like to thank Dr. Erik Runkle for serving as my major professor and for his guidance, support, and expertise throughout my graduate experience. I also wish to thank my graduate committee members Dr. Bert Cregg, for providing statistical consultation, and Dr. Frank Telewski, for his assistance with leaf sectioning. Dr. Ryan Warner and Dr. Veronica Vallejo were generous to allow me to use their laboratory facilities and for being a resource of knowledge. I also wish to thank Dr. Randy Beaudry for his support in evaluating chlorophyll assays. I would like to thank Mike Olrich for his trouble-shooting expertise and his technical assistance with experiments, Cathy Whitman for her advice, and Dr. Bridget Behe for her mentorship. I also wish to thank Allen Pyle from Rakers for being so cooperative in filling my plug tray requests promptly. Furthermore, the following graduate students and staff were generous to provide their assistance, support, and friendship: William Lindberg, Daedre Craig, Tasneem Vaid, Qingwu Meng, Vickie Wang, Jenn Evans, Wei-Kuang Lin, Brent Crain, Nate DuRussel, Jennifer Sweet, and Allison Jones. The following undergraduate students, who assisted me in collecting data, were extremely helpful and I very much appreciate their efforts: Mina Hirzel, Kyle Barasier, Chris Tolksdorf, Clarissa Richardson, Lindsey Garner, and Rose Merril. In addition, I would like to thank Juan David Munoz for his statistical advising. Finally, I wish to thank all of those people in the horticulture office and in the department for their friendship and encouragement. iii TABLE OF CONTENTS LIST OF TABLES ......................................................................................................................... vi LIST OF FIGURES ...................................................................................................................... vii SECTION I LITERATURE REVIEW ................................................................................................................1 Literature Review: Light Emitting Diodes for the Horticultural Industry .......................................2 Lighting Technologies Used in Horticulture ..............................................................................2 Plant Pigments and the Mechanisms of Photosynthesis and Respiration ...................................6 Photoreceptors Regulate Plant Growth and Development........................................................10 Interactions of Light Quality and Quantity and Carbon Dioxide on Plant Growth .............13 Plant Acclimation to Light Quality and Quantity ................................................................14 Plant Growth Responses to Light Quality ...........................................................................15 UV Effects on Plant Growth and Protective Compound Accumulation ..............................21 Advantages and Barriers to LED Implementation in Horticulture ...........................................22 APPENDIX ....................................................................................................................................24 LITERATURE CITED ..................................................................................................................26 SECTION II GROWTH RESPONSES OF ORNAMENTAL ANNUAL SEEDLINGS UNDER DIFFERENT WAVELENGTHS OF RED LIGHT PROVIDED BY LIGHT-EMITTING DIODES ................33 Abstract .....................................................................................................................................35 Introduction ...............................................................................................................................36 Materials and Methods ..............................................................................................................38 Expt. 1. The effect of red light wavelengths on plant growth ..............................................38 Light environments .........................................................................................................39 Data collection and analysis............................................................................................40 Expt. 2. The effect of R light ratios at two intensities .........................................................41 Chlorophyll assay............................................................................................................41 Results .......................................................................................................................................42 Expt. 1. Leaf area and number .............................................................................................42 Seedling height..............................................................................................................42 Fresh shoot weight ........................................................................................................43 Dry shoot weight ...........................................................................................................43 Expt 2. Leaf area and number ............................................................................................44 Seedling height..............................................................................................................45 Fresh shoot weight ........................................................................................................45 Dry shoot weight ...........................................................................................................45 Chlorophyll concentration ............................................................................................45 Discussion .................................................................................................................................46 Summary ...................................................................................................................................50 iv APPENDIX ...............................................................................................................................52 LITERATURE CITED .............................................................................................................61 SECTION III GROWTH ACCLIMATION OF SEEDLINGS TO BLUE, GREEN, AND RED LIGHT FROM LIGHT-EMITTING DIODES AT A FIXED IRRADIANCE.......................................................65 Abstract .....................................................................................................................................67 Introduction ...............................................................................................................................67 Materials and Methods ..............................................................................................................70 Light treatments and environment .......................................................................................71 Data collection .....................................................................................................................72 Statistical analysis ................................................................................................................73 Results .......................................................................................................................................73 Leaf number and relative leaf area .......................................................................................73