Bhuiyan Ruqayah, van Iersel Marc W
Horticultural Physiology Laboratory, Department of Horticulture, University of Georgia, Athens, GA, United States.
Front Plant Sci. 2021 Jan 28;12:619973. doi: 10.3389/fpls.2021.619973. eCollection 2021.
The cost of providing lighting in greenhouses and plant factories can be high. In the case of variable electricity prices, providing most of the light when electricity prices are low can reduce costs. However, it is not clear how plants respond to the resulting fluctuating light levels. We hypothesized that plants that receive a constant photosynthetic photon flux density (PPFD) will produce more biomass than those grown under fluctuating light levels. To understand potential growth reductions caused by fluctuating light levels, we quantified the effects of fluctuating PPFD on the photosynthetic physiology, morphology, and growth of 'Little Gem' and 'Green Salad Bowl' lettuce. Plants were grown in a growth chamber with dimmable white LED bars, alternating between high and low PPFDs every 15 min. The PPFDs were ∼400/0, 360/40, 320/80, 280/120, 240/160, and 200/200 μmol⋅m⋅s, with a photoperiod of 16 h and a DLI of ∼11.5 mol⋅m⋅day in all treatments. CO was ∼800 μmol⋅mol. Plants in the 400/0 μmol⋅m⋅s treatment had ∼69% lower A, (net assimilation averaged over 15 min at high and 15 min at low PPFD) than plants grown at a PPFD of 320/80 μmol⋅m⋅s (or treatments with smaller PPFD fluctuations). The low A, in the 400/0, and to a lesser extent the 360/40 μmol⋅m⋅s treatment was caused by low net assimilation at 360 and 400 μmol⋅m⋅s. Plants grown at 400/0 μmol⋅m⋅s also had fewer leaves and lower chlorophyll content compared to those in other treatments. The four treatments with the smallest PPFD fluctuations produced plants with similar numbers of leaves, chlorophyll content, specific leaf area (SLA), dry mass, and leaf area. Chlorophyll content, A,, and dry mass were positively correlated with each other. Our results show that lettuce tolerates a wide range of fluctuating PPFD without negative effects on growth and development. However, when fluctuations in PPFD are extreme (400/0 or 360/40 μmol⋅m⋅s), chlorophyll levels and A, are low, which can explain the low poor growth in these treatments. The ability of lettuce to tolerate a wide range of fluctuating light levels suggests that PPFD can be adjusted in response to variable electricity pricing.
在温室和植物工厂中提供照明的成本可能很高。在电价可变的情况下，在电价较低时提供大部分光照可以降低成本。然而，目前尚不清楚植物如何应对由此产生的光照水平波动。我们假设，接受恒定光合光子通量密度（PPFD）的植物比在波动光照水平下生长的植物产生更多的生物量。为了了解光照水平波动导致的潜在生长减少情况，我们量化了波动的PPFD对“小宝石”和“绿色沙拉碗”生菜的光合生理、形态和生长的影响。植物在一个带有可调光白色LED灯条的生长室中生长，每隔15分钟在高PPFD和低PPFD之间交替。PPFD分别为~400/0、360/40、320/80、280/120、240/160和200/200 μmol·m·s，所有处理的光周期为16小时，日累积光量（DLI）约为11.5 mol·m·天。二氧化碳浓度约为800 μmol·mol。与在320/80 μmol·m·s（或PPFD波动较小的处理）下生长的植物相比，400/0 μmol·m·s处理的植物净同化率（在高PPFD下15分钟和低PPFD下15分钟的净同化平均值）低约69%。400/0处理以及在较小程度上360/40 μmol·m·s处理下的低净同化率是由360和400 μmol·m·s下的低净同化引起的。与其他处理相比，在400/0 μmol·m·s下生长的植物叶片也更少，叶绿素含量更低。PPFD波动最小的四个处理产生的植物叶片数量、叶绿素含量、比叶面积（SLA）、干质量和叶面积相似。叶绿素含量、净同化率和干质量之间呈正相关。我们的结果表明，生菜能够耐受广泛的PPFD波动，而不会对生长和发育产生负面影响。然而，当PPFD波动极端（400/0或360/40 μmol·m·s）时，叶绿素水平和净同化率较低，这可以解释这些处理中生长不良的原因。生菜耐受广泛光照水平波动的能力表明，可以根据可变电价调整PPFD。
