LIGHT-EMITTING DIODE LIGHTING FOR FOREST NURSERY SEEDLING PRODUCTION^©

Crop lighting is an energy-intensive necessity for nursery production of high-quality native plants and forest tree seedlings. During the winter months (especially in northern USA latitudes) or overcast or cloudy days, the amount of solar radiation reaching greenhouse crops is insufficient resulting in growth cessation, early terminal bud formation, and failure of seedlings to reach target height for outplanting (Tinus, 1995; Lopez and Runkle, 2008). In light of this, nursery growers have added supplemental lighting to increase the daily light integral (DLI), defined as the photosynthetic light received over the course of the day for seedling production (Torres and Lopez, 2010). A wide range of supplemental light sources are used in nurseries to control plant development and manipulate plant quality (Tinus, 1995; Bourget, 2008). However, the problem with most lighting systems, such as high-pressure sodium (HPS) lamps, is that they do not provide the light spectrum that is most efficient for photosynthesis in plants. In addition, because of the huge amount of electrical energy required, using HPS as supplemental lighting, for most reforestation and native plant nurseries, is economically impractical.
The light-emitting diode (LED) is key to improving energy utilization for greenhouse lighting. Light-emitting diodes are solid-state, robust, very long-lived, and are designed to produce the exact light quality that plants can utilize for photosynthesis while using only a fraction of the electricity used by HPS, the current industry standard (Bourget, 2008). Thus, any new lighting technology that significantly reduces electricity consumption for crop lighting while producing top quality seedlings for ecological restoration and conservation efforts has significant benefits to society. The objective of the current study was to examine the effect of supplemental lighting provided by LED and HPS on growth and chlorophyll concentrations of Douglas fir (DF, Pseudotsuga menziesii) and Engelmann spruce (ES, Picea engelmannii) seedlings from British Columbia, Idaho, and New Mexico (northern, central, and southern populations, respectively).