2018 ASHS Annual Conference

Light-emitting diodes (LEDs) becomes popular supplemental lighting (SL) in greenhouse because of energy saving without compensating crop productivity. Accumulation of phytochemicals can be also induced by LEDs with specific spectrum in many crop species. However, recent study shows that phytochemical properties of greenhouse tomatoes remain unchanged in response to red (R, 600-700 nm), blue (B, 400-500 nm), and far-red (FR, 700-750 nm) SL from LEDs since the dynamic light environment in greenhouse nullifies the effects of wavelengths of light. Besides secondary metabolites, mineral nutrients are essential components for human nutrition and contribute to the quality and flavor of tomatoes. Ion uptake, translocation, and assimilation are also highly dependent on photosynthesis and photomorphogenesis, and therefore, responses of tomatoes to B, the signal of sunlight, and FR, the signal of shading, could be dramatically different in terms of ion utilization. The objectives of this study were to determine how different light quality affects ion accumulation, partitioning, and fruit quality of high-wire greenhouse tomato. ‘Merlice’ scions grafted onto ‘Maxifort’ rootstocks were supplemented with different combinations of B, R, and FR LED lighting: B + R (39%B∶61%R), R + high FR (71%R∶29%FR), or R only (100%R). 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%. The concentration of nitrate, nitrite, sulfate, phosphate, chloride, sodium, potassium, magnesium, and calcium in leaf, stem, root, and fruit were determined by ion chromatography. On a whole plant scale, B increased the accumulation of nitrite and calcium while FR reduced their accumulation. Particularly, B increased the partitioning of phosphate to stem while FR decreased it. B also increased the partitioning of calcium from stem to leaf; however, FR increased its partitioning from stem to fruit in association with higher dry mass allocation to fruit relative to stem. The concentrations of sulfate and sodium were increased by 300% and 27% by adding FR to R, suggesting that FR improves the quality and flavor of tomato. Our results suggest that FR light reverses the action of B light in the accumulation and partitioning of some ions and mineral composition of tomato can be manipulated by additional FR light.