Browsing by Author "Craver, Joshua, advisor"
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Item Open Access Characterizing acclimation of pansy and petunia to CO₂ enrichment for controlled environment production(Colorado State University. Libraries, 2021) McKinney, David Wayne, author; Craver, Joshua, advisor; Pilon-Smits, Elizabeth, committee member; Bauerle, Bill, committee memberWhile crops often respond immediately to enriched CO2 concentrations (e.g., increased photosynthesis), this initial response is often not sustained throughout production, reducing the benefit of this input. For horticulture species, the timing and extent of these acclimation responses is still widely uncertain. Therefore, the objective of this research was to determine species-specific acclimation responses to enriched CO2 concentrations for pansy (Viola ×wittrockiana 'Matrix Blue Blotched Improved') and petunia (Petunia ×hybrida 'Dreams Midnight) during both propagation and finishing. To investigate the effects of enriched CO2 concentrations on pansy and petunia during finishing production, seedlings were transplanted into 11.5-cm pots and placed in growth chambers with air temperature, relative humidity, and radiation intensity setpoints of 21 °C, 55%, and 250 µmol∙m–2∙s–1, respectively. Carbon dioxide treatments were established using the two growth chambers with setpoints of either 400 (ambient) or 1000 μmol·mol–1 (enriched) maintained during a 16-h photoperiod. In addition to data collected through destructive harvest, rate of photosynthesis (A) in response to increasing internal leaf CO2 concentration (A-Ci) and ambient CO2 concentration (A-Ca) were measured weekly with a portable leaf photosynthesis system at saturating (A-Ci; 1000 µmol∙m–2∙s–1) or production (A-Ca; 250 µmol∙m–2∙s–1) radiation intensities. For both pansy and petunia, plants grown under the enriched CO2 concentration produced higher total shoot dry mass compared to ambient after 4 weeks. However, decreased maximum rate of photosynthetic electron transport (Jmax), maximum rate of Rubisco carboxylase (Vcmax), and similar photosynthesis at operating Ci concentration were observed under the enriched CO2 concentration after 4 weeks. Additionally, A measured at 1000 and 400 μmol·mol–1 was lower for both pansy and petunia grown under the enriched compared to ambient CO2 concentration based on A-Ca responses after 1 week, further indicating quick physiological acclimation to this input. This indicates little benefit of elevated CO2 to increase plant quality during the finishing stage of production in pansy and petunia, however there is possible marginal benefit due to increased biomass with no effect on overall plant size. To evaluate the impact of CO2 enrichment at varying timing and duration during propagation, pansy and petunia seeds were sown in 128-cell trays and placed in growth chambers with air temperature, relative humidity, and radiation intensity setpoints of 21 °C, 55%, and 250 µmol∙m–2∙s–1, respectively. Carbon dioxide treatments were established using the two growth chambers with setpoints of either 400 (ambient) or 1000 μmol·mol–1 (enriched) maintained during a 16-h photoperiod. Treatments consisted of seedlings grown for 28 days at ambient (Amb28), 28 days at elevated (Elv28), 14 days at ambient then 14 days at elevated (Amb14:Elv14), and 14 days at elevated then 14 days at ambient CO2 concentration (Elv14:Amb14). Harvest data was collected weekly, and four weeks after germination seedlings were transplanted into the greenhouse to determine impacts on finishing quality and flowering. Pansy and petunia produced higher total dry mass (roots + leaves + stem) under Elv28 and Amb14:Elv14 compared to Amb28 after 4 weeks, but showed no difference in leaf area. Additionally, plants grown under Elv28 and Amb14:Elv14 produced higher leaf mass area than Amb28 and Elv14:Amb14 for both species. Pansy showed decreased days to flower under Elv28, but no difference in biomass or size after transplant into the greenhouse. Therefore, elevated CO2 during seedling production may influence days to flower but does not contribute to growth rate long term after transplant. Likewise, similar morphological responses can be achieved with elevated CO2 being applied during the last two weeks of seedling production compared to elevation throughout the propagation stage. These results provide useful information regarding the timing and extent of physiological acclimation in response to enriched CO2 concentrations for pansy and petunia. However, due to physiological acclimation potentially occurring within one week of treatment initiation, additional research is needed to best understand how this input can be further optimized for controlled environment production.Item Open Access Dynamic manipulation of far-red light and temperature for the production of microgreens in controlled environments(Colorado State University. Libraries, 2024) Fulton, Oliver Wynne, author; Craver, Joshua, advisor; Bousselot, Jennifer, committee member; Johnson, Sarah, committee memberMicrogreens are becoming increasingly popular for controlled environments due to their ease of production, profitability, and high concentration of nutrients. However, to date there is little information on how light spectra and temperature interactively affect plant growth and morphology to optimize the production of horticultural crops, including microgreens. Therefore, the objective of this study was to investigate the benefit of reducing air temperature as well as supplementing with far-red (700-750 nm) photons to enhance the morphology and phytochemical concentrations of three Brassica microgreen species. Seeds of mustard (Brassica juncea 'Garnet Giant'), kohlrabi (Brassica oleracea var. gongylodes), and red cabbage (Brassica oleracea var. capitata) were sown on rockwool substrate and grown in walk-in growth chambers using ebb and flow hydroponic systems at the CSU Spur campus. Upon germination, microgreens were grown under ambient air temperature of either 18 or 21 °C and subjected to the following lighting treatments: photosynthetic photon flux density (PPFD) of 165 μmol·m−2·s−1 (PAR165); PPFD of 200 μmol·m−2·s−1 (PAR200); and PPFD of 165 μmol·m−2·s−1 + 35 μmol·m−2·s−1 of far-red light (PAR165+FR35). Expected shade avoidance responses (e.g., increased hypocotyl elongation) due to a low R:FR value occurred in all three species under PAR165+FR35, regardless of temperature. Additionally, fresh weight of red cabbage and kohlrabi was greatest under PAR165+FR35 or similar between PAR165+FR35 and PAR200, respectively, at both temperatures. While an interaction with temperature was not observed, results support the role of far-red light in the manipulation of both microgreen quality and biomass accumulation. A follow-up experiment was conducted with red cabbage microgreens grown under the previous far-red lighting treatment (PAR165+FR35) to explore the dynamic manipulation of air temperature throughout production. While production under PAR165+FR35 should result in characteristic shade avoidance responses, including a potential decrease in pigmentation, we hypothesized that a reduction in air temperature during production could serve as a secondary stressor to increase phytochemical concentrations (e.g., anthocyanins). Using the same experimental setup described for the previous experiment, red cabbage microgreens were grown at an air temperature of 21 °C for 12 days (Control) or moved 6, 8, 10, or 11 days after sowing to an air temperature of 16 °C. Shade avoidance responses (e.g., hypocotyl elongation) and both fresh and dry weight were reduced for microgreens transferred to the air temperature of 16 °C on days 6 and 10 compared to all other treatments. Interestingly, microgreens transferred to the air temperature of 16 °C resulted in greater dry weight compared to Control. While results were not significant, an anticipated trend of increased relative anthocyanin content in response to longer durations at the 16 °C air temperature was observed. Although the dynamic manipulation of both far-red light and temperature could lead to microgreens with optimal yield, morphological characteristics, and phytochemical concentrations, future research is warranted to elucidate target environmental setpoints, durations, and possible interactions.Item Open Access Using far-red light to promote leaf expansion for young plant production(Colorado State University. Libraries, 2022) Percival, Anthony Christophe, author; Craver, Joshua, advisor; Newman, Steven, committee member; Peers, Graham, committee memberAt northern latitudes, a reduction in the natural light quantity during the winter production of young annual bedding plants (plugs) often necessitates the use of supplemental lighting to reach a target daily light integral (DLI) to ensure high plug quality. However, the low leaf area index (LAI) of plugs during the initial stages of production suggests that a portion of applied light is not intercepted by leaves. Because electric lighting represents a significant percentage of total production costs for greenhouses utilizing supplemental lighting, minimizing wasted light (photons not absorbed by the plant) is critical. Some species have shown an increase in leaf area in response to growth under light with a low ratio of red to far-red light (R:FR); this is generally considered as a shade avoidance response to improve light capture, but there is considerable variation across species. An early increase in leaf area would allow for more effective light capture by seedlings and a reduction in wasted light, but other shade avoidance responses such as elongation of stems and petioles are undesirable for plug production and could outweigh benefits of leaf expansion. Far-red mediated shade avoidance responses may also depend on background photosynthetic photon flux density, DLI, and temperature. The objective of this research was to investigate the effects of far-red radiation on leaf expansion and other shade avoidance responses for the popular annual bedding plant, Petunia ×hybrida (petunia), and to examine potential influences of other environmental variables. Reducing the R:FR in a greenhouse environment with supplemental lighting is challenging due to the relatively high proportion of natural light, so an end-of-day far-red (EOD-FR) lighting strategy was utilized to investigate the promotion of leaf expansion by far-red light for seedings of petunia 'Wave Purple', and 'Dreams Midnight'. Seedlings were grown in 128-cell trays in a common greenhouse environment under an ambient DLI of 5.26 mols·m-2·d-1 to simulate a winter light environment. Seedlings received no EOD-FR, supplemental lighting for the duration of the experiment, or one of the following EOD-FR treatments that varied in far-red intensity, R:FR ratio, and treatment duration: 10 μmol·m-2·s-1 of far-red light (R:FR ~0.8) for 30 minutes, 10 or 20 μmol·m-2·s-1 of far-red light (R:FR ~0.15) for 30 minutes, or 20 μmol·m-2·s-1 of far-red light (R:FR ~0.15) for 240 minutes. In addition to end-of-day (EOD) treatments, some seedlings under EOD-FR were moved under supplemental lighting after 2 or 3 weeks of EOD lighting. Destructive data was collected 2, 3, and 4 weeks after treatment initiation. Seedlings that received EOD-FR lighting showed stem elongation responses, and seedlings under the lower R:FR or longer EOD duration resulted in greater elongation, but no EOD treatment resulted in an increase in leaf area compared to control (no supplemental lighting or EOD lighting) or supplemental lighting treatments. Results of this study indicate that under low DLIs, EOD-FR light applied in the first three weeks of seedling production does not promote early leaf area expansion and reduces seedling quality under these experimental conditions. To further examine leaf expansion as a response to far-red radiation, seedlings of petunia 'Dreams Midnight' were grown for 28 days under the recommended target DLI of ~10 mols·m-2·d-1 using a 17.25-h photoperiod with either a high (~10.8) or low R:FR (~0.50). The effects of EOD-FR were also examined by subjecting seedlings grown under the high R:FR to a 1-hour low intensity (target total photon flux density of 46 μmol·m2·s-1) EOD lighting application with a very low R:FR (0.15). Lastly, the influence of temperature on the effects of far-red radiation were examined by growing seedlings at either 16 or 21 ℃ for the duration of the experiment, and by moving plants from a high R:FR in the 21 ℃ chamber during the day to the 16 ℃ chamber for the EOD-FR treatment and subsequent dark period. Overall, seedlings grown at a constant air temperature of 16 ℃ displayed stunted growth (lower leaf area, number of leaves, and total biomass) compared to those grown at 21 ℃ regardless of lighting treatment. At 21 ℃, the use of EOD-FR did not promote an increase in leaf area. Seedlings grown under a constant low R:FR (~0.50) at 21 ℃ did display increased leaf area, but lower stem dry mass per unit length (mg·mm-1), leaf mass per unit area (g·m2), and root dry mass indicated poor seedling quality. These results further show that morphological responses to far-red light are species-specific, and that plant responses to far-red light may differ based on a variety of environmental factors. Future research regarding leaf expansion in response to far-red light that incorporates other environmental factors (e.g., temperature, TPFD, photoperiod length) may lead to a more complete understanding of species-specific shade avoidance responses, and further work in this area may assist growers with the development of far-red lighting strategies to improve light capture and seedling quality for young plant production.