The photosynthetic action spectrum compares the relative photosynthetic QY per wavelength, and indicates that wavelengths between 575 and 675 nm are ~30% more efficient for photosynthesis than photons in the blue waveband (400–500 nm). The wavelength-dependent photosynthetic efficiency can be determined by the photosynthetic quantum yield (QY), a measure of the production of oxygen or consumption of carbon dioxide, for various crops 5, 6. Spectral quality is an important growth parameter since the efficiency of photosynthesis is dependent on the wavelength of the photon absorbed by the plant. While PPFD and DLI are important plant growth parameters for characterizing plant development, they ignore spectral quality differences of radiation received by the plant. The PPFD a plant receives in a 24 h day is measured as the daily light integral (DLI, mol m −2 d −1) and is directly proportional to the rate of plant growth, which is subsequently determined as biomass accumulation. The amount of PAR photons a plant receives is quantified by the photosynthetic photon flux density (PPFD, μmol m −2 s −1), which is the number of photosynthetically active photons per unit area per second. The 400–700 nm waveband of the electromagnetic spectrum primarily powering photosynthesis is referred to as photosynthetically active radiation (PAR). Furthermore, recirculating hydroponic plant nutrient delivery systems recycle water for greatest RUE 4. This greater productivity results from optimized environmental controls, year-round production, and reduced pests and diseases. CEA affords crop production with the highest resource use efficiency (RUE), and exceeds the annual per-area yield of field agriculture tenfold 3. For resilience against these threats, producers of vegetable crops have turned to controlled environment agriculture (CEA) as a solution. Spectral modifications by the luminescent QD films improved photosynthetic efficiency in lettuce and could enhance productivity in greenhouses on Earth, or in space where, further conversion is expected from greater availability of ultraviolet photons.Īs anthropogenic climate change exacerbates the severity and frequency of extreme weather events 1, arable farmland is decreasing due to overpopulation and drought 2.
Lettuce grown under the 600 and 660 nm-emitting QD films respectively increased edible dry mass (13 and 9%), edible fresh mass (11% each), and total leaf area (8 and 13%) compared with under a control film containing no QDs. All plant growth parameters, except for spectral quality, were uniform across three production environments.
CuInS 2/ZnS quantum dot (QD) films were used to down-convert ultraviolet/blue photons to red emissions centered at 600 and 660 nm, resulting in increased biomass accumulation in red romaine lettuce. To improve plant productivity in BLSS, the quality of the solar spectrum can be modified by lightweight, luminescent films. Bioregenerative life-support systems (BLSS) involving plants will be required to realize self-sustaining human settlements beyond Earth.
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