2018 ASHS Annual Conference

Advances in light-emitting diode (LED) technology over the past few decades have brought about the ability to fine-tune lighting systems for plant production in controlled environments. Light-emitting diodes are also a valuable tool for physiologists interested in understanding the phenotype of plants when exposed to different spectra of light. Translocation is an under-explored, fundamental process involving carbon and water balance affecting source/sink relationships. Source leaf strength is defined by photosynthesis and carbon export; both processes being essential for growth. The process of carbon export involves additional steps downstream of photosynthesis including multiple cell lines, enzymes, and transporters which can be environmentally regulated. Our primary objective was to examine diurnal patterns of photosynthesis and carbon export via ¹⁴CO₂ steady-state labelling under different spectra generated by LEDs, but at similar CO₂ influx rates. Daily patterns showed that photosynthesis and export were supported by all wavelengths of light tested including orange and green alone. Export in the light, under all wavelengths was always higher than that at night, varying from 65-83% of daily carbon fixation depending on light intensity. Photosynthesis and export were highly correlated under all wavelengths (r=0.90-0.96). Relative export decreased as photosynthesis increased under all wavelengths indicating an upper limit for export. Interestingly, only at the medium photosynthetic rate were differences found. At this rate, relative export under blue and orange LEDs were higher than under white and red-white LEDs. Furthermore, we also investigated the relationship between carbon export and water status. The current hypothesis is that transpiration and carbon export are linked in woody species. However, so far, our data with tomato under different spectral quality are inconclusive. Understanding the phenotypic responses of the carbon export pathway to light can aid in the optimization and implementation of LED lighting systems for controlled environment crop production.