Growth responses of tomato plants to different wavelength ratios of amber, red, and blue light

Abstract

The differential effects of light quality and quantity are under scrutiny so that energy-efficient plant production may be optimized. This study aimed to determine the combined effects of amber (595 nm), red (635 nm), and blue (445 nm) wavelengths at different light intensities on tomato plant growth. Plants were treated for 12 days with combined light-emitting diode (LED) wavelengths, at a photosynthetic photon flux density (PPFD) ranging from 232 to 1660 μmol m−2s−1 with a 16 h d−1 photoperiod. Mean fresh mass of tomato plants treated with amber-red light (AR) was 22% greater than plants treated with blue-amber (BA) light and 67% greater than blue-red (BR) light. Plants treated with BA exhibited 36% greater fresh mass than plants treated with BR light. Mean dry mass of plants treated with AR light was 30% greater compared to BR light, and the dry mass of plants treated with BA and BR was statistically similar. Plants grown under BR had 28% and 35% smaller leaf area compared with those grown under BA and AR, respectively. Mean height of the plants treated with AR increased by 24 and 52% compared to plants grown under BA and BR lights, respectively. Maximum stem diameter was observed at 1000 μmol m−2s−1 for AR and BA, and 1200 μmol m−2s−1 for BR. Specific leaf area (SLA) decreased with the increase of PPFD levels up to 1000 μmol m−2s−1 for all the light treatments. A PPFD above 1000 μmol m−2s−1 showed an increase in SLA for plants cultivated with AR and AB. SLA for plants treated with RB was stable above 1000 μmol m−2s−1 PPFD levels. Plants treated with BR light had 25 and 38% higher chlorophyll content compared to plants treated with BA and AR light, respectively. Maximum yield and chlorophyll content data indicate that using Chl content to correlate full plant photosynthetic and growth potential is inappropriate. Findings suggest that a high percentage of amber light (>75%) in a full-spectrum LED regimen may augment controlled environment crop production.