Light-emitting diode (LED) technology shows promise for supplementing photosynthetically active radiation (PAR) in forest nurseries because of the potential reduction in energy consumption and an ability to supply discrete wavelengths to optimize seedling growth. Our objective was to examine the effects of light spectra supplied by LED and traditional high-pressure sodium (HPS) lamps on growth and physiology of Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) and Engelmann spruce (Picea engelmannii Parry ex Engelm.) seedlings. We used three latitudinal sources for each species: British Columbia (BC), Idaho (ID), and New Mexico (NM). Container seedlings were grown for 17 weeks in the greenhouse under an 18 h photoperiod of ambient solar light supplemented with light delivered from HPS or LED. In general, seedlings grown under LED had significantly greater growth, gas exchange rates, and chlorophyll contents than those seedlings grown under HPS. The growth and physiological responses to supplemental lighting varied greatly among species and seed sources. Generally, LED-grown seedlings from BC had the greatest growth and tissue dry mass followed by ID and NM populations. Compared with HPS, the significant increase in seedling growth and concomitant energy savings with LED (29% energy consumption relative to HPS) demonstrates the promise of using LED as PAR supplemental lighting for container seedling production.
