The Effect of Red & Blue Rich LEDs vs Fluorescent Light on Lollo Rosso Lettuce Morphology and Physiology

Abstract

The challenges of feeding an increasing population, an increasingly urban population and within an increasingly challenging global environment have focused ideas on new ways to grow food. Growing food in a controlled environment (CE) is not new but new technologies such as broad-spectrum LEDs and robotics are generating new opportunities. Growth recipes can be tailored to plant species in a CE and plasticity in plant responses to the environment may be utilized to make growth systems more efficient for improved yield and crop quality. Light use efficiency within CE must consider energy requirements, yield and impacts on quality. We hypothesized that understanding how plants change their morphology and physiology in response to light will allow us to identify routes to make light more efficient for delivery of high-quality produce. We focused on responses to light in Lollo rosso lettuce which produces compact, crinkly and highly pigmented leaves. We compared the spectra of the commonly used artificial light sources in indoor farming (compact fluorescence tubes, FL, and broad-spectrum light-emitting diodes, LEDs) at two irradiance levels (270 and 570 μmol m–2 s–1). We discovered LEDs (λP: 451, 634, and 665 nm) produced the same amount of produce for half the incident energy of FL (T5). At higher irradiances LEDs produced 9% thicker leaves, 13% larger rosettes and 15% greater carotenoid content. Leaves differed in light absorptance with plants grown under lower FL absorbing 30% less of mid-range wavelengths. We show that the relative efficiencies of LED and FL is a function of the irradiances compared and demonstrate the importance of understanding the asymptotes of yield and quality traits. Increasing our understanding of structural and biochemical changes that occur under different combination of wavelengths may allow us to better optimize light delivery, select for different ranges of plasticity in crop plants and further optimize light recipes.

High Light Intensity from Blue-Red LEDs Enhance Photosynthetic Performance, Plant Growth, and Optical Properties of Red Lettuce in Controlled Environment

“…Increasing light intensity decreased leaf greenness, Chl pigments, and PRI indexes according to LUE decrease, while the ARI1 and ARI2, indexes related to anthocyanin content, and the carotenoid reflectance index CRI2 increased with increasing irradiance. This indicates a predominant role at the photosystem level of anthocyanins and carotenoids in photoprotective action rather than the thermal dissipation mechanism, since WUE int was not affected and leaf photosynthesis increased [47,48].…”

Ratio of Intensities of Blue and Red Light at Cultivation Influences Photosynthetic Light Reactions, Respiration, Growth, and Reflectance Indices in Lettuce

“…In recent years, numerous studies (e.g., [ 50 , 51 , 52 , 75 , 76 ]) that have investigated the influence of LED illumination with different intensity ratios of red and blue light on lettuce growth, productivity, biochemical composition, and many other parameters, have been published. In particular, there are works that directly analyze the photosynthetic parameters [ 41 , 46 , 75 , 77 ] and leaf optical properties [ 44 ] in lettuce plants that have been cultivated under different light spectra.…”

“…In general ([ 38 , 39 , 40 , 41 , 42 ]), blue light stimulates chloroplast development, the production of photosynthetic pigments, and photosynthetic processes and inhibits growth; red light has the opposite influence. Combinations of LEDs with both red and blue spectra (or with the red, blue, and white/green spectra) are an effective tool for the plant cultivation because they support relatively high photosynthetic and growth processes [ 38 , 39 , 40 , 43 , 44 , 45 ]; in contrast, adding far-red light can decrease the growth and photosynthetic parameters in plants [ 43 ]. It is important to note that adding even a small portion of blue light (<10–20%) to red light can strongly stimulate photosynthetic and growth processes [ 46 , 47 ].…”

“…The following supporting information can be downloaded at: . Figure S1: Example of the estimation of the green area on plants using ImageJ, including the initial image (a) and image with green areas marked (b); Table S1: List of reflectance indices automatically calculated by the PolyPen RP 410 UVIS software in accordance with [ 44 ] and used in the present work.…”

LED Lighting and High-Density Planting Enhance the Cost-Efficiency of Halimione Portulacoides Extraction Units for Integrated Aquaculture

“…Providing optimal and energy-efficient lighting conditions is paramount for commercial plant production [27], and solid-state LED lighting is nowadays considered the most flexible and cost-efficient technology for indoor hydroponics because it provides better control over different light parameters (e.g., spectrum, irradiance, photosynthetically active radiation) [28]. Different light spectra produced by LEDs, particularly red and blue, have been shown to influence the productivity of conventional leafy-green crops, and results suggest a general improvement in performance relative to other types of artificial lighting (e.g., fluorescence) and natural lighting [29][30][31][32][33][34]. Yet, the influence of different light spectra in the development of halophyte crops is still relatively understudied [35][36][37].…”