2018 ASHS Annual Conference

Supplemental lighting (SL) is necessary for optimal plant growth and yield in greenhouse tomato production, particularly during winter months in temperate climates. Over-head (OH) high-pressure sodium (HPS) lamps presently are the most common type of SL because of their high-intensity capabilities. The leaves at high canopy receive more light than the leaves at low canopy due to light gradient caused by OH-HPS and shading of high canopy on low canopy. Intracanopy (IC)-light-emitting diode (LED) towers provide a uniform lighting environment vertically along the plant canopy without emitting radiant heat and have a more efficient light spectrum to enhance photosynthesis. Ion uptake, partitioning and assimilation are highly dependent on photosynthesis and transpiration. However, there is no report about how microenvironment created by light resource affects photosynthesis and transpiration, thus ion accumulation, partitioning and fruit quality. The objective of this study was to determine how different SL sources [OH-HPS vs. IC-LED] affect ion accumulation, partitioning and fruit quality of high-wire greenhouse tomato. ‘Merlice’ scions grafted onto ‘Maxifort’ rootstocks were supplemented with IC-LED (100% red light) and OH-HPS (4% blue light: 48% green light: 48% red light). Un-supplemental lighting control (ULC) was also included. Plants were fertigated with a commercial complete fertilizer mix (4.5N–14P–34K; CropKing, Lodi, OH) to maintain acceptable electrical conductivity and pH in the root zone, and irrigation duration and frequency were adjusted to provide a daily leaching fraction of 30%. Photosynthetic and transpiration rates were measured with a portable photosynthesis system. The concentration of nitrate, nitrite, sulfate, phosphate, chloride, sodium, potassium, magnesium and calcium in leaf, stem, root and fruit were determined by ion chromatography. Compared to OH-HPS, IC-LED-grown tomato with uniform lighting accumulates more nitrate, nitrite, sodium, potassium, magnesium and calcium in whole plant due to higher photosynthesis and dry mass accumulation. Vertical light gradient of OH-HPS induced stem elongation and higher biomass allocation to stem, which significantly increased the partitioning of sodium, potassium and calcium to stem compared to IC-LED. Moreover, OH-HPS induced more partitioning of nitrate from root to leaf compared to ULC resulting from higher transpiration at higher canopy. Compared to OH-HPS, IC-LED increased concentration of manganese by 38% and lowers the concentration of sulfate by 68% in tomato fruits, which may improve the fruit quality and aroma. Overall, IC-LED optimized photosynthesis, thus ion uptake, partitioning and assimilation, possibly improving fruit quality and aroma.