Plant Factories Are Heating Up: Hunting for the Best Combination of Light Intensity, Air Temperature and Root-Zone Temperature in Lettuce Production

Abstract

This study analyzed interactions among photon flux density (PPFD), air temperature, root-zone temperature for growth of lettuce with non-limiting water, nutrient, and CO2 concentration. We measured growth parameters in 48 combinations of a PPFD of 200, 400, and 750 μmol m–2 s–1 (16 h daylength), with air and root-zone temperatures of 20, 24, 28, and 32°C. Lettuce (Lactuca sativa cv. Batavia Othilie) was grown for four cycles (29 days after transplanting). Eight combinations with low root-zone (20 and 24°C), high air temperature (28 and 32°C) and high PPFD (400 and 750 μmol m–2 s–1) resulted in an excessive incidence of tip-burn and were not included in further analysis. Dry mass increased with increasing photon flux to a PPFD of 750 μmol m–2 s–1. The photon conversion efficiency (both dry and fresh weight) decreased with increasing photon flux: 29, 27, and 21 g FW shoot and 1.01, 0.87, and 0.76 g DW shoot per mol incident light at 200, 400, and 750 μmol m–2 s–1, respectively, averaged over all temperature combinations, following a concurrent decrease in specific leaf area (SLA). The highest efficiency was achieved at 200 μmol m–2 s–1, 24°C air temperature and 28°C root-zone temperature: 44 g FW and 1.23 g DW per mol incident light. The effect of air temperature on fresh yield was linked to all leaf expansion processes. SLA, shoot mass allocation and water content of leaves showed the same trend for air temperature with a maximum around 24°C. The effect of root temperature was less prominent with an optimum around 28°C in nearly all conditions. With this combination of temperatures, market size (fresh weight shoot = 250 g) was achieved in 26, 20, and 18 days, at 200, 400, and 750 μmol m–2 s–1, respectively, with a corresponding shoot dry matter content of 2.6, 3.8, and 4.2%. In conclusion, three factors determine the “optimal” PPFD: capital and operational costs of light intensity vs the value of reducing cropping time, and the market value of higher dry matter contents.

Water content, carbohydrate accumulation, and secondary metabolites in Allium victorialis sprouts exposed to shoot cutting in varied irradiations

“…Lighting spectral characteristic is a flexible instrument which can be controlled to meet target demand at a cost (Lu, 2021). The adjustment of spectrum not only promotes crop yield ( Saito et al, 2020;Carotti et al, 2021), but also boosts production of officinal ingredients in medicinal plants Feldzensztajn et al, 2021). The specific illumination condition established for medicinal plants depends on how it affects the production of secondary metabolites.…”

Divergent Leaf Morpho-Physiological and Anatomical Adaptations of Four Lettuce Cultivars in Response to Different Greenhouse Irradiance Levels in Early Summer Season

“…Considering that the optimal temperatures for lettuce growth range from 18 to 28 • C, high-temperature stress combined with a long day induces alterations in water relations, photosynthetic activity, osmolyte accumulation and hormone production [12,13]. Other than leading to quality degradation [14], these changes lead to a lower marketable yield of lettuce, which is affected by dry matter and water content [15]. To avoid these adverse effects, off-season lettuce production requires adequate crop protection from high solar radiation.…”

The Impact of LED Light Spectrum on the Growth, Morphological Traits, and Nutritional Status of ‘Elizium’ Romaine Lettuce Grown in an Indoor Controlled Environment

“…These results suggest that the faster the biomass production is, the more often tipburn symptoms occur on young romaine lettuce leaves. It is known that climatic factors such as high temperature and high light intensity, leading to the rapid growth of lettuce shoots, are conducive to the occurrence of tipburn [41][42][43] and that this is a genetically determined trait [30,42,[44][45][46].…”