While greenhouse design varies in sophistication, all greenhouses utilize covers that transmit photosynthetically active radiation (PAR; 400–700 nm) to crops grown inside. These covering materials can have different transmission characteristics including spectral distribution, photosynthetic photon flux density (PPFD; 400–700 nm), and diffuseness (i.e., light scattering). Such characteristics can independently or interactively impact the growth and development of greenhouse crops. There is increasing interest in developing and integrating advanced greenhouse covers with 1) photovoltaic (PV) materials that generate electricity to power mechanical equipment or provide an additional, passive income source for growers; and 2) fluorescent pigments that alter the solar spectrum to potentially increase crop growth and yield. Despite their potential, their short- and long-term effects on greenhouse crop yield and quality are largely unknown. Thus, the objective of this research was to evaluate the growth, flowering, and fruiting of economically important greenhouse crops under experimental transparent PV panels and red-fluorescent covers to inform further development and ultimately application in greenhouse-based horticulture.The integration of PV panels in agriculture, commonly referred to as "agrivoltaics", is a possible solution to concurrently address the rising global energy and food demand while considering land-use efficiency. As PV materials have developed technologically, they can now be designed to selectively transmit PAR and potentially be integrated into greenhouse structures. However, a tradeoff is created where PV materials and plants compete for the same resource – solar energy. The tradeoffs of PV panel absorption (for electricity generation) and transmission (for plant growth) of various light wavebands are not well understood. Therefore, we evaluated the effects of neutral-density and experimental, photoselective PV materials that primarily absorbed photons between 400 and 850 nm on commercially important crop types of leafy greens, culinary herbs, fruiting crops, and floriculture crops. Regardless of the transmitted photon distribution, the best predictor of crop yield and quality was the average daily light integral (DLI; 400–700 nm). Over multiple years of research, leafy greens, culinary herbs, and floriculture crops exhibited greater tolerance to PV shading than fruiting crops and therefore have the greatest potential for cultivation in agrivoltaic systems. In contrast, PV shading decreased the yield of fruiting crops. Our findings collectively suggest that PV panels with the greatest PAR transmission (i.e., primarily absorb photons <400 and >700 nm) are the most suitable for greenhouse applications. At the same PPFD, decreasing the intensity of blue (B; 400–499 nm) and green (G; 500–599 nm) light and increasing the intensity of red (R; 600–699 nm) light can potentially increase plant biomass accumulation. This can be attributed to a higher photosynthetic efficiency of R light compared to B and G light, as well as greater leaf expansion and photon interception in a low B-light environment. Spectrum-shifting films absorb B and G light and amplify R light, and to a lesser extent, far-red (FR; 700–750 nm) light. However, this spectral conversion decreases the transmitted PPFD. Our objective was to determine whether a red-fluorescent material would increase biomass accumulation of various greenhouse crops despite the reduction in DLI. In an initial study, a red-fluorescent material increased the shoot fresh mass (SFM) of lettuce (Lactuca sativa) by up to 45%, depending on cultivar, compared to a neutral-density (unpigmented) plastic with a 10–25% higher transmitted PPFD. Cultivars with the greatest increase in SFM also had greater leaf area, projected canopy area, and/or plant diameter. In a second study, a red-fluorescent material increased the SFM of lettuce by 17–27% compared to a neutral-density plastic with a similar transmitted DLI, but this effect was not consistent among fruiting or floriculture crops. These experimental results enhance our understanding of the interplay between light quality and intensity on crop growth and opportunities and limitations of using red-fluorescent plastics and transparent PV panels in greenhouse horticulture.
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