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Article

Increasing Growth of Lettuce and Mizuna under Sole-Source LED Lighting Using Longer Photoperiods with the Same Daily Light Integral

Department of Horticulture, University of Georgia, Athens, GA 30602, USA
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Author to whom correspondence should be addressed.
Agronomy 2020, 10(11), 1659; https://doi.org/10.3390/agronomy10111659
Received: 9 October 2020 / Revised: 23 October 2020 / Accepted: 24 October 2020 / Published: 28 October 2020
(This article belongs to the Special Issue Role of Vertical Farming in Modern Horticultural Crop Production)
Light recommendations for horticultural crops often focus on the optimal daily light integral (DLI) without regard to how that light is delivered throughout each day. Because photosynthesis is more efficient at lower photosynthetic photon flux density (PPFD), we hypothesized that longer photoperiods with lower PPFD results in faster growth than shorter photoperiods with higher PPFD and the same DLI. We quantified the effect of different photoperiods, all providing the same DLI, on photosynthesis and growth of two leafy greens. Mizuna (Brassica rapa var. japonica) and lettuce (Lactuca sativa) “Little Gem” were grown from seed in a controlled environment chamber (20 °C and 819 µmol·mol−1 CO2) under six photoperiods (10, 12, 14, 16, 18, and 20 h). LED fixtures provided white light and PPFD was adjusted so each treatment received a DLI of 16 mol·m−2·d−1. Mizuna and lettuce were harvested 30 and 41 days after planting, respectively. Longer photoperiods with lower PPFD increased light interception, chlorophyll content index, quantum yield of photosystem II, and aboveground biomass, but decreased instantaneous CO2 assimilation of lettuce and mizuna. Aboveground biomass increased 16.0% in lettuce and 18.7% in mizuna in response to increasing the photoperiod from 10 to 20 h. In summary, extending the photoperiod and lowering PPFD increases growth of lettuce and mizuna by increasing light interception and the quantum yield of photosystem II. View Full-Text
Keywords: Brassica rapa var. japonica; Lactuca sativa; light-emitting diodes; leafy greens; light interception; photosynthesis; plant factory Brassica rapa var. japonica; Lactuca sativa; light-emitting diodes; leafy greens; light interception; photosynthesis; plant factory
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MDPI and ACS Style

Palmer, S.; van Iersel, M.W. Increasing Growth of Lettuce and Mizuna under Sole-Source LED Lighting Using Longer Photoperiods with the Same Daily Light Integral. Agronomy 2020, 10, 1659. https://doi.org/10.3390/agronomy10111659

AMA Style

Palmer S, van Iersel MW. Increasing Growth of Lettuce and Mizuna under Sole-Source LED Lighting Using Longer Photoperiods with the Same Daily Light Integral. Agronomy. 2020; 10(11):1659. https://doi.org/10.3390/agronomy10111659

Chicago/Turabian Style

Palmer, Shane, and Marc W. van Iersel 2020. "Increasing Growth of Lettuce and Mizuna under Sole-Source LED Lighting Using Longer Photoperiods with the Same Daily Light Integral" Agronomy 10, no. 11: 1659. https://doi.org/10.3390/agronomy10111659

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