Growth and Photosynthesis of Young <i>Cymbidium</i> as Influenced by Supplemental Lighting Timing

Abstract

The effects of supplemental lighting (SL) timing on vegetative growth and the photosynthetic assimilation rate of young Cymbidium hybrids were examined. Nine month old C. ‘Yang Guifei’ and ‘Wine Shower’ were treated with four different SL timings: 22:00 – 02:00 (middle of the night, MN); 17:00 – 21:00 (end of day extension, DE); 07:00 – 09:00 plus 17:00 – 19:00 (both beginning and end of the night as split day extension, SDE), and non SL (8/16 h, short day, SD) for 4 months. All SL were provided by two types of 100% red LEDs (640 and 660 nm), with 150 μmol･m-2 ･s-1 and 800 μmol･mol-1 of CO2 supplied during the night (16 h). Pseudobulb diameters were significantly higher under SL treatments compared with the SD of both cultivars, irrespective of SL timing. Net photosynthetic assimilation rates were enhanced with increased SL, due to the additional photosynthesis and reduction of dark respiration. Thus, daily net photosynthetic amounts of SL treatments effectively increased photosynthesis compared to the SD. These results indicate that SL helps promote vegetative growth by enhancing photosynthesis. Since there were no significant differences among the SL timings when CO2 was provided uniformly during the night, we concluded that growth and photosynthesis of young Cymbidium do not depend on the timing of SL application, but are related to the daily light integrals, which is the amount of photosynthetically active photons delivered over 24 hours.