2018 ASHS Annual Conference

Advancements in light-emitting diode (LED) technology have made them a viable alternative to current lighting systems for both sole and supplemental lighting requirements. Much research is available on the wavelength specific responses of leaves from multiple crops when exposed to long-term wavelength specific lighting. However, leaf responses to environmental stimuli do not always extrapolate linearly to whole plant responses due to the complexities of the plant canopy, namely mutual shading and leaves of different ages. For these reasons, we measured the diurnal whole plant CO₂ and H₂O gas exchange of vegetative tomato plants under both long-term and short-term exposure to various spectral qualities as well as ambient and elevated CO₂ conditions. It was determined that within each environmental stimulus provided to the plant, biomass gain throughout the day was similar when plants were measured under high-pressure sodium (HPS), red-blue LED, or red-white LED. Under all luminary systems, tomato plants showed a similar diurnal pattern of transpiration, rising to a maximum around mid-day and declining during the remainder of the photoperiod. However, plants measured under the LED lighting systems produced higher transpiration rates than plants measured under HPS lights. This conversely lead to decreased water-use-efficiency (WUE) rates throughout the day. The decrease in WUE from plants exposed to both LED systems was ubiquitous within all lighting and CO­₂ conditions tested. The understanding of the effects of wavelength specific lighting on both CO₂ and H₂O canopy gas exchanges have significant implications for both academic research where plants are cultivated in controlled research environments and commercial greenhouse production.