*Article* **Green Light Improves Photosystem Stoichiometry in Cucumber Seedlings (***Cucumis sativus***) Compared to Monochromatic Red Light**

**Nicholas B. Claypool and J. Heinrich Lieth \***

Plant Sciences, University of California, Davis, CA 95616, USA; nbclaypool@gmail.com

**\*** Correspondence: jhlieth@ucdavis.edu

**Abstract:** It has been shown that monochromatic red and blue light influence photosynthesis and morphology in cucumber. It is less clear how green light impacts photosynthetic performance or morphology, either alone or in concert with other wavelengths. In this study, cucumber (*Cucumis sativus*) was grown under monochromatic blue, green, and red light, dichromatic blue–green, red–blue, and red–green light, as well as light containing red, green, and blue wavelengths, with or without supplemental far-red light. Photosynthetic data collected under treatment spectra at light-limiting conditions showed that both red and green light enhance photosynthesis. However, photosynthetic data collected with a 90% red, 10% blue, 1000 µmol photons m−<sup>2</sup> s −1 , saturating light show significantly lower photosynthesis in the green, red, and red–green treatments, indicating a blue light enhancement due to photosystem stoichiometric differences. The red–green and green light treatments show improved photosynthetic capacity relative to red light, indicating partial remediation by green light. Despite a lower quantum efficiency and the lowest ambient photosynthesis levels, the monochromatic blue treatment produced among the tallest, most massive plants with the greatest leaf area and thickest stems.

**Keywords:** blue light; *Cucumis sativus L.* (cucumber); green light; light-emitting diode (LED); morphology; photosynthesis; red light; intrinsic water use efficiency (iWUE); photostationary state of phytochrome (PSS); photosynthetic photon flux density (PPFD); yield photon flux (YPF)
