Increasing duration and intensity of nighttime supplemental lighting promotes growth and photosynthesis in young Cymbidium plants

Abstract

This study was conducted to determine how nighttime supplemental lighting (NSL) duration and light intensity influence the growth and photosynthesis of young Cymbidium plants. Seven-month-old Cymbidium ‘Yang Guifei’ and ‘Wine Shower’ plants were grown under five NSL durations (2, 4, 6, 8, and 16 h) and three NSL light intensities (10, 100, and 200 µmol·m−2·s−1) for 4 months, which provided 16 NSL light integrals ranging from 0 to 11.52 mol·m−2·d−1 including 0 h NSL treatment. The NSL treatments were provided by 100% red LEDs, and CO2 was supplied during the nighttime (16 h) at 800 µmol·mol−1. Pseudobulb diameter, the number of leaves, and biomass accumulation significantly increased with increasing NSL duration and light intensity in both cultivars. These growth characteristics showed increasing trends with increasing NSL light integrals. In particular, pseudobulb diameter increased by 33 and 43% in ‘Yang Guifei’ and ‘Wine Shower,’ respectively, as the NSL light integral increased from 0 to 11.52 mol·m−2·d−1. Relative chlorophyll contents decreased with increasing NSL light intensity in ‘Yang Guifei’. Photosynthetic assimilation rate (An) during NSL was promoted in response to increases of NSL duration and light intensity in both cultivars, implying that the An increased with increasing NSL light integrals. However, in this study, continuous lighting (16 h NSL) limited daytime photosynthesis. Daily An showed a positive correlation with pseudobulb diameter. These results indicated that NSL could accelerate the growth of young Cymbidium plants by inducing nighttime photosynthesis. In this study, considering that continuous NSL could inhibit the daytime photosynthesis, the 8 h NSL with 200 µmol·m−2·s−1 treatment was the most effective for promoting the growth. This finding can be used to maximize the growth rate and shorten the cultivation time in Cymbidium production.