S06 - Session O2 - Novel supplementary lighting protocols for optimising controlled environment horticulture.

Authors: Margaret Ahmad *, Blanche Aguida, Laurence Bourgeois-Racetted

The effect of light on economically important traits in plants growth is well known, and there has been much research into how wavelength, intensity, duration, and quality of light can be manipulated to promote desired horticultural traits. However, lighting strategies to date have focused primarily on the photosynthetically active (daytime) period, whereas, with the exception of classic photoperiodism 'night break' experiments, almost no data is available on the effect of providing supplemental lighting during the dark (non-photosynthetic) phase of plant growth. Here we show how providing Far Red High Irradiance lighting supplements throughout the dark (night) can dramatically improves plant growth and development, particularly of those exposed to suboptimal indoor lighting conditions. Plants are grown in environmentally controlled growth chambers ( 10 - 14 hour days) at either optimal or sub-threshold (limiting) photosynthetic light intensity. High Irradiance Infrared Light (720 n 750nm specialty LED sources) is applied exclusively during the night period. The effect on parameters including seedling and plant elongation growth, leaf expansion, biomass, fruit size and time to flowering are measured in a variety of plant species including Arabidopsis , rosacea, strawberry, lettuce, geranium, and tomato. Infra Red light is not absorbed by the phososynthetic pigments and does not affect the plant sleep n wake cycles. Here we show that a variety of both ornamental and crop plants exposed to HIR (high irradiance) Infrared Light resulted in significantly accelerated stem elongation, leaf expansion, increased chlorophyll content, increased total biomass, and accelerated time to flowering. This was especially true for plants grown under limiting light conditions, with up to 10 n fold increase in biomass. This lighting supplement solution thereby provides a cost-effective means of improving growth of greenhouse plants. These effects will be discussed with respect to the underlying plant photobiological mechanisms.