Next Article in Journal
Variations of Essential Oil Constituents in Oregano (Origanum vulgare subsp. viridulum (= O. heracleoticum) over Cultivation Cycles
Next Article in Special Issue
Light Quality Affected the Growth and Root Organic Carbon and Autotoxin Secretions of Hydroponic Lettuce
Previous Article in Journal
Chitosan Modified Biochar Increases Soybean (Glycine max L.) Resistance to Salt-Stress by Augmenting Root Morphology, Antioxidant Defense Mechanisms and the Expression of Stress-Responsive Genes
Previous Article in Special Issue
Quality of Supplementary Morning Lighting (SML) During Propagation Period Affects Physiology, Stomatal Characteristics, and Growth of Strawberry Plants
Article

Longer Photoperiods with the Same Daily Light Integral Increase Daily Electron Transport through Photosystem II in Lettuce

Department of Horticulture, University of Georgia, Athens, GA 30602, USA
*
Author to whom correspondence should be addressed.
Plants 2020, 9(9), 1172; https://doi.org/10.3390/plants9091172
Received: 27 July 2020 / Revised: 4 September 2020 / Accepted: 7 September 2020 / Published: 10 September 2020
Controlled environment crop production recommendations often use the daily light integral (DLI) to quantify the light requirements of specific crops. Sole-source electric lighting, used in plant factories, and supplemental electric lighting, used in greenhouses, may be required to attain a specific DLI. Electric lighting is wasteful if not provided in a way that promotes efficient photochemistry. The quantum yield of photosystem II (ΦPSII), the fraction of absorbed light used for photochemistry, decreases with increasing photosynthetic photon flux density (PPFD). Thus, we hypothesized that the daily photochemical integral (DPI), the total electron transport through photosystem II (PSII) integrated over 24 h, would increase if the same DLI was provided at a lower PPFD over a longer photoperiod. To test this, ΦPSII and the electron transport rate (ETR) of lettuce (Lactuca sativa ‘Green Towers’) were measured in a growth chamber at DLIs of 15 and 20 mol m−2 d−1 over photoperiods ranging from 7 to 22 h. This resulted in PPFDs of 189 to 794 μmol m−2 s−1. The ΦPSII decreased from 0.67 to 0.28 and ETR increased from 55 to 99 μmol m−2 s−1 as PPFD increased from 189 to 794 μmol m−2 s−1. The DPI increased linearly as the photoperiod increased, but the magnitude of this response depended on DLI. With a 7-h photoperiod, the DPI was ≈2.7 mol m−2 d−1, regardless of DLI. However, with a 22-h photoperiod, the DPI was 4.54 mol m−2 d−1 with a DLI of 15 mol m−2 d−1 and 5.78 mol m−2 d−1 with a DLI of 20 mol m−2 d−1. Our hypothesis that DPI can be increased by providing the same DLI over longer photoperiods was confirmed. View Full-Text
Keywords: photochemistry; daily photochemical integral; electron transport; quantum yield of photosystem II; chlorophyll fluorescence; photoperiod photochemistry; daily photochemical integral; electron transport; quantum yield of photosystem II; chlorophyll fluorescence; photoperiod
Show Figures

Graphical abstract

MDPI and ACS Style

Elkins, C.; van Iersel, M.W. Longer Photoperiods with the Same Daily Light Integral Increase Daily Electron Transport through Photosystem II in Lettuce. Plants 2020, 9, 1172. https://doi.org/10.3390/plants9091172

AMA Style

Elkins C, van Iersel MW. Longer Photoperiods with the Same Daily Light Integral Increase Daily Electron Transport through Photosystem II in Lettuce. Plants. 2020; 9(9):1172. https://doi.org/10.3390/plants9091172

Chicago/Turabian Style

Elkins, Claudia, and Marc W. van Iersel 2020. "Longer Photoperiods with the Same Daily Light Integral Increase Daily Electron Transport through Photosystem II in Lettuce" Plants 9, no. 9: 1172. https://doi.org/10.3390/plants9091172

Find Other Styles
Note that from the first issue of 2016, MDPI journals use article numbers instead of page numbers. See further details here.

Article Access Map by Country/Region

1
Back to TopTop