Light irradiance level for optimal growth and nutrient contents in borage microgreens

Abstract

In this study we used the combination red (638, 665 nm), blue (445 nm) and far red (735 nm) light-emitting diodes (LEDs) to obtain the different light irradiance photosynthetic photon flux densities (PPFDs) of uniform spectra and investigated the effects of different light irradiance levels (110-545 μmol m-2s-1) on growth and nutrient contents in borage (Borago officinalis L.) microgreens cultivated in closed controlled environment chambers (21/17°C, 16 h photoperiod). The results showed that fresh weight, leaf area increased and hypocotyls length decreased with increasing PPFD from 110 to 440 μmol m-2s-1; when the highest investigated PPFD level of 545 μmol m-2s-1 resulted in inhibited biomass growth and undesired hypocotyl elongation. The lowest nitrate contents were determined in microgreens cultivated under moderate, 330-440 μmol m-2s-1 irradiance levels. 440 μmol m-2s-1 PPFD level evoked the response of protective antioxidant system and resulted in the highest contents of the main antioxidant phytochemicals, when 545 μmol m-2s-1 PPFD level suppressed antioxidant levels in borage microgreens. Our results implied that, compared to other light irradiance treatments, 440 μmol m-2s-1 was more suitable for borage microgreens cultivation.