Canopy Size and Light Use Efficiency Explain Growth Differences between Lettuce and Mizuna in Vertical Farms

Abstract

Vertical farming is increasingly popular due to high yields obtained from a small land area. However, the energy cost associated with lighting of vertical farms is high. To reduce this cost, more energy efficient (biomass/energy use) crops are required. To understand how efficiently crops use light energy to produce biomass, we determined the morphological and physiological differences between mizuna (Brassica rapa var. japonica) and lettuce (Lactuca sativa ‘Green Salad Bowl’). To do so, we measured the projected canopy size (PCS, a morphological measure) of the plants throughout the growing cycle to determine the total amount of incident light the plants received. Total incident light was used together with the final dry weight to calculate the light use efficiency (LUE, g of dry weight/mol of incident light), a physiological measure. Plants were grown under six photosynthetic photon flux densities (PPFD), from 50 to 425 µmol m–2 s–1, for 16 h d–1. Mizuna and lettuce were harvested 27 and 28 days after seeding, respectively. Mizuna had greater dry weight than lettuce (P < 0.0001), especially at higher PPFDs (PPFD ≥ 125 µmol m–2 s–1), partly because of differences in the projected canopy size (PCS). Mizuna had greater PCS than lettuce at PPFDs ≥ 125 µmol m–2 s–1 and therefore, the total incident light over the growing period was also greater. Mizuna also had a higher LUE than lettuce at all six PPFDs. This difference in LUE was associated with higher chlorophyll content index and higher quantum yield of photosystem II in mizuna. The combined effects of these two factors resulted in higher photosynthetic rates in mizuna than in lettuce (P = 0.01). In conclusion, the faster growth of mizuna is the result of both a larger PCS and higher LUE compared to lettuce. Understanding the basic determinants of crop growth is important when screening for rapidly growing crops and increasing the efficiency of vertical farms.

Effects of Light Spectral Quality on the Micropropagated Raspberry Plants during Ex Vitro Adaptation

“…It has decreased significantly only in response to red light proportion fall from 50% to 37% (treatments 1 and 2, respectively). Both high Φ PSII and high chlorophyll content may increase the ETR, CO 2 assimilation rate, and potentially the growth rate of plants [ 54 ], as it was also observed in treatment 5 in our experiment.…”

“…It shows that some disorders could occur in the photosynthetic apparatus. To understand how different lighting strategies to influence plant growth, it is important to determine ΦPSII since this partly determines how efficiently they use the absorbed light for photosynthesis and biomass production [ 54 ]. Decreased ratio of R 660 in the spectrum of incident light resulted in the increased quantum yield of photosystem II.…”

Optimization of Photosynthetic Photon Flux Density and Light Quality for Increasing Radiation-Use Efficiency in Dwarf Tomato under LED Light at the Vegetative Growth Stage

“…In addition, PPFD increased Pn (Figure 2) but reduced pLUE (Table 3). Jayalath and van Iersel [10] also reported that a high PPFD decreased the RUE by reducing the quantum yield of photosystem II. In Experiment 1, the RUE of plants in W300 was the highest among the three treatments.…”

“…Radiation-use efficiency (RUE) is a good index for measuring radiation utilization by plants [8,9] and an important quantifier of crop production in relation to photosynthesis, as it combines both the amount of radiation captured by the crop and the production of dry matter. PPFD can influence the RUE of plants by affecting the photosynthetic rate [10], stomatal behavior [11,12], photosynthate distribution [13,14], and chlorophyll content [15,16]. RUE is the highest under a PPFD of 200 µmol m −2 s −1 in lettuce and under a PPFD of 250 µmol m −2 s −1 in basil [17].…”

Variations in the Growth of Cotyledons and Initial True Leaves as Affected by Photosynthetic Photon Flux Density at Individual Seedlings and Nutrients

“…Plant phenotyping is a set of methodologies and protocols used to study plant performance, growth, architecture, and composition at different scales of organization, from organs to canopies, and it elucidates the plant trait dynamics in a non-destructive and non-invasive manner [5,14,[19][20][21]. Having great potential for application to commercial PFALs [22], imagebased studies in PFALs have been conducted, including quantifying the projected leaf area (value measured by 2D camera images captured from above the plant canopy or seedling trays) of the plant canopy [15,[23][24][25][26][27][28].…”