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

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. <br>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.

本研究探究了在水分、养分与CO₂浓度均无限制的条件下，光子通量密度（PPFD）、空气温度与根区温度对生菜生长的影响。我们设置了3种PPFD水平（200、400、750 μmol·m⁻²·s⁻¹，光照时长16 h），搭配20、24、28、32℃共4种空气温度与4种根区温度，形成48组处理组合并测定其生长参数。供试生菜品种为巴塔维亚·奥蒂莉（Lactuca sativa cv. Batavia Othilie），整个栽培周期包含4个循环（移栽后29天）。其中8组根区温度偏低（20和24℃）、空气温度偏高（28和32℃）且PPFD较高（400和750 μmol·m⁻²·s⁻¹）的组合出现了严重的叶缘焦枯病（tip-burn），未纳入后续分析。随着PPFD升高至750 μmol·m⁻²·s⁻¹，生菜干物质质量随之增加。<br>空气温度对鲜产量的影响与所有叶片扩展过程均相关。比叶面积（Specific Leaf Area，SLA）、地上部生物量分配比例与叶片含水量随空气温度的变化趋势一致，均在24℃左右达到峰值。根区温度的影响相对较弱，在几乎所有处理条件下，其最优值均在28℃左右。在此温度组合下，当PPFD分别为200、400和750 μmol·m⁻²·s⁻¹时，生菜达到商品规格（地上部鲜重250 g）所需的时间分别为26、20和18天，对应的地上部干物质含量分别为2.6%、3.8%与4.2%。综上，三大因素决定了“最优”PPFD：光照强度的基建与运营成本、缩短种植周期所带来的收益，以及更高干物质含量的市场价值。