Lettuce Leaf Optical Properties: Linking Spectral Characteristics to Photosynthetic Productivity

Abstract

Green leafy vegetables are the main crops in the novel type of controlled environment horticulture – plant factories. This type of cultivation system enables full control of environmental parameters, therefore allow to predict the timing and quality of vegetable production. However, to control these processes properly, efficient, non-destructive analysis method to evaluate plant wellness is necessary. In this study, we review how the light emitting diode (LED) lighting spectrum affect growth and photosynthetic parameters of lettuces and analyze the relations between these parameters and leaf optical indices, measured using the non-destructive spectrometric method. Green baby leaf lettuces (Lactuca sativa ‘Lobjoits green cos’) were cultivated in closed environment growth chambers (21/17°C day/night temperature, ~55% relative humidity). Lettuces were cultivated under different LED lighting spectra: combinations of red (660, 638 nm), blue (445 nm) and far-red (735 nm) with supplemental green (530 nm), orange (620 nm), yellow (595 nm) and UV-A (385 nm) wavelengths, total photosynthetic photon flux density 300 μmol m-2s-1. At the maturity stage, leaf reflection and absorption spectra were registered, stomatal parameters and photosynthetic parameters evaluated. The obtained results show, that leaf optical properties depend on LED lighting spectrum, as well as on other cultivation environment parameters. The main correlations and interfaces will be discussed.