Study on spectral response of saffron (Crocus sativus L.) at different leaf ages and evaluation on photosynthetic energy efficiency of narrow-band LED spotlights

Abstract

Leaf photosynthesis largely determines the daughter corm yields in vegetative growth for saffron (Crocus sativus L.). Most of previous researches focuses on spectral response in various species, but lacking the study on saffron leaves at different leaf ages. In this study, the action spectrum based on photosynthetic photon flux density (PPFD) and irradiance were distinguished and interpretated. The optical properties and photosynthetic performances of leaves were respectively investigated at two leaf ages, dependence on customized narrow-band LED spotlights from 380 nm to 780 nm with an interval 20 nm and a band width 10 nm. The younger leaves charactered higher reflectance and transmittance at 500 − 600 nm, resulting in lower absorptance compared to the older leaves. The spectral response curves including action spectrum and quantum yield for younger leaves were higher than the older, but their relative curves displayed coincidence. The spectral response curves exhibited two peaks at 440 and 640 nm, but not low between 500 and 600 nm. Nevertheless, the photosynthetic energy efficiency of spotlights demonstrated very low in green/yellow region. Accordingly, more attentions should be paid to green and yellow LED lighting during the vegetative stage for saffron, as well as improving their manufacturing technology.