Abstract
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.
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Claims 7
Claim · model-written summary
Quantum yield of PSII decreased from 0.67 to 0.28 as PPFD increased from 189 to 794 μmol m−2 s−1.
- Taxon
- Lettuce
Lactuca sativat0 - Treatment
- PPFDe1
- Outcome
- ΦPSIIe1
- Direction
- decreasede1
- Value
- from 0.67 to 0.28e1
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e1“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”
t0“Lettuce”
Claim · model-written summary
Electron transport rate increased from 55 to 99 μmol m−2 s−1 as PPFD increased from 189 to 794 μmol m−2 s−1.
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e1“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”
t0“Lettuce”
Claim · model-written summary
DPI increased linearly with photoperiod, with a magnitude that depended on DLI.
- Taxon
- LettuceLactuca sativat0
- Treatment
- photoperiode2
- Outcome
- DPIe2
- Direction
- increasede2
- Qualifier
- magnitude of this response depended on DLIe2
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e2“The DPI increased linearly as the photoperiod increased, but the magnitude of this response depended on DLI”
t0“Lettuce”
Claim · model-written summary
With a 7-h photoperiod, DPI was about 2.7 mol m−2 d−1 regardless of DLI.
- Taxon
- LettuceLactuca sativat0
- Treatment
- 7-h photoperiode3
- Outcome
- DPIe3
- Direction
- no_changeinferrede3
- Value
- ≈2.7 mol m−2 d−1e3
- Qualifier
- regardless of DLIe3
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e3“With a 7-h photoperiod, the DPI was ≈2.7 mol m−2 d−1, regardless of DLI”
t0“Lettuce”
Claim · model-written summary
With a 22-h photoperiod and DLI of 15 mol m−2 d−1, DPI was 4.54 mol m−2 d−1.
- Taxon
- LettuceLactuca sativat0
- Treatment
- 22-h photoperiode4
- Outcome
- DPIe4
- Value
- 4.54 mol m−2 d−1e4
- Qualifier
- DLI of 15 mol m−2 d−1e4
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e4“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”
t0“Lettuce”
Claim · model-written summary
With a 22-h photoperiod and DLI of 20 mol m−2 d−1, DPI was 5.78 mol m−2 d−1.
- Taxon
- LettuceLactuca sativat0
- Treatment
- 22-h photoperiode4
- Outcome
- DPIe4
- Value
- 5.78 mol m−2 d−1e4
- Qualifier
- DLI of 20 mol m−2 d−1e4
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e4“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”
t0“Lettuce”
Claim · model-written summary
Providing the same DLI over longer photoperiods increased DPI, as the hypothesis predicted.
- Taxon
- LettuceLactuca sativat0
- Treatment
- providing the same DLI over longer photoperiodse5
- Outcome
- DPIe5
- Direction
- increasede5
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e5“Our hypothesis that DPI can be increased by providing the same DLI over longer photoperiods was confirmed”
t0“Lettuce”
The same questions in other papers
light · physiology: photosynthesis · Lactuca sativa (garden lettuce)Positive and negative results
55 papers in the same direction as this paper · 17 in the opposite direction · 2 reporting no difference from an alternative
- positive
- positive
- positive
71 papers more in this group
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