Growth and acclimation of impatiens, salvia, petunia, and tomato seedlings to blue and red light

Abstract

Plant growth is plastic and adaptive to the light environment; characteristics such as extension growth, architecture, and leaf morphology change, depending on the light spectrum. Although blue (B; 400–500 nm) and red (R; 600–700 nm) light are generally considered the most efficient wavelengths for eliciting photosynthesis, both are often required for relatively normal growth. Our objective was to quantify how the B:R influenced plant seedling growth and morphology and understand how plants acclimated to these light environments. We grew seedlings of three ornamental annuals and tomato under six sole-source light-emitting diode (LED) lighting treatments or one cool-white fluorescent treatment that each delivered a photosynthetic photon flux (PPF) of 160 mmol·m-2·s–1 for 18 h·dL1. The following treatments were provided with B (peak = 446 nm) and R (peaks = 634 and 664 nm) LEDs: B160 (160 mmol·m-2·s-1 of B light only), B80+R80, B40+R120, B20+R140, B10+R150, and R160. Seedlings of impatiens (Impatiens walleriana), salvia (Salvia splendens), petunia (Petunia 3hybrida), and tomato (Solanum lycopersicum) were grown for 31 to 37 days at a constant 20 8C. Plants with as little as 10 mmol·m-2·s-1 of B light were 23% to 50% shorter and had 17% to 50% smaller leaves than plants under only R light. Impatiens and salvia had 53% to 98% greater fresh shoot weight under treatments without B light than with ‡80 mmol·m-2·sL1. Plants grown under fluorescent lamps had the greatest chlorophyll content but also had among the thinnest leaves of treatments. Blue-rich light increased flowering in impatiens and reduced incidence of intumescences on tomato. We conclude that, in sole-source lighting of propagules, B light inhibits leaf and stem expansion, which subsequently limits photon capture and constrains biomass accumulation. As little as 10 mmol·m-2·s-1 of B light in an R-dominant background can elicit desirable growth responses for the production of young plants and for other situations in which compact growth is desired.