Effect of Pre-Harvest Supplemental UV-A/Blue and Red/Blue LED Lighting on Lettuce Growth and Nutritional Quality

Triston Hooks,Joseph Masabni,Genhua Niu,Ling Sun

doi:10.3390/horticulturae7040080

Abstract

Blue light and ultra-violet (UV) light have been shown to influence plant growth, morphology, and quality. In this study, we investigated the effects of pre-harvest supplemental lighting using UV-A and blue (UV-A/Blue) light and red and blue (RB) light on growth and nutritional quality of lettuce grown hydroponically in two greenhouse experiments. The RB spectrum was applied pre-harvest for two days or nights, while the UV-A/Blue spectrum was applied pre-harvest for two or four days or nights. All pre-harvest supplemental lighting treatments had a same duration of 12 h with a photon flux density (PFD) of 171 μmol m−2 s−1. Results of both experiments showed that pre-harvest supplemental lighting using UV A/Blue or RB light can increase the growth and nutritional quality of lettuce grown hydroponically. The enhancement of lettuce growth and nutritional quality by the pre-harvest supplemental lighting was more effective under low daily light integral (DLI) compared to a high DLI and tended to be more effective when applied during the night, regardless of spectrum.

Highlights

Greenhouse hydroponic production of leafy greens is expanding globally and is an important component of the world’s food supply [1]
SPAD is an indicator of the “greenness” or relative chlorophyll content in the leaves and is used as an indicator of plant health [39], but has been associated with darker colored and thicker leaves [27]. These results indicate that UV-A/Blue and red and blue (RB) light can influence plant morphology by increasing leaf dry matter and thickness and reducing leaf area
Dou et al [27] reported that the pre-harvest UV-B light treatment had a bigger increase in concentrations of anthocyanin, phenolics, and flavonoids in basil (Ocimum basilicum) under a lower photosynthetic photon flux density (PPFD) compared to higher PPFD. Both experiments showed that pre-harvest supplemental light treatments using UV-A/Blue light or RB light can increase lettuce growth and quality in a greenhouse hydroponic system

Summary

Introduction

Greenhouse hydroponic production of leafy greens is expanding globally and is an important component of the world’s food supply [1]. Supplemental lighting is commonly used to enhance plant growth and improve quality in greenhouse crop production when natural light is inadequate [2]. The electricity cost of supplemental lighting can be significant for a commercial greenhouse, accounting for as much as 30% of the farm gate value [4]. There is a need to improve the cost-effectiveness of greenhouse supplemental lighting for long-term sustainable food production. An alternative to supplemental lighting throughout the production cycle is to incorporate it for only a short period before harvest (pre-harvest) to improve the growth and quality of leafy greens [5]. Depending on the duration and efficiency of the supplemental lighting, the consumption of electricity can be significantly reduced [6]

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