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- Author or Editor: David L. Bubenheim x
- HortScience x
The role of spectral quality and CO2 concentration in environmental control of lignin synthesis in spring wheat is being studied by the NASA Controlled Ecological Life Support System Program (CELSS). Wheat cultivars were exposed to four different spectral environments provided by 1) metal halide lamps (MH), 2) high pressure sodium lamps (HPS), 3) low pressure sodium lamps (LPS; almost monochromatic, 589 nm), or 4) LPS plus low irradiance blue light (5 μmol m-2 s-1; LPS + Blue) at equal photosynthetic photon flux. Stem lignin content was suppressed 25% under the LPS compared with the MH and HPS; blue addition (LPS + Blue) resulted in 25% greater lignin content compared with the LPS alone and 8% suppression compared with MH and HPS. CO2 studies compared lignin content of wheat grown in the field, greenhouse at 350 μmol mol-1 CO2, and growth chambers at 350 and 700 μmol mol-1 CO2, Lignin content was greatest and equal in the field and growth chamber at 700 μmol mol-1 CO2. Lowest lignin content was measured in the growth chamber at 350 μmol mol-1 CO2; lignin content in the greenhouse was intermediate between that measured in the field and growth chamber at 350 μmol mol-1 CO2, Additional CO2 studies in controlled environments will be discussed.
Electronic dimming of high-intensity discharge lamps offers control of photosynthetic photon flux (PPF) but is often characterized as causing significant spectral changes. Growth chambers with 400-W metal halide (MH) and high-pressure sodium (HPS) lamps were equipped with a dimmer system using silicon-controlled rectifiers (SCR) as high-speed switches. Phase control operation turned the line power off for some period of the alternating current cycle. At full power, the electrical input to HPS and MH lamps was 480 W (root mean squared) and could be decreased to 267 W and 428 W, respectively, before the arc was extinguished. Concomitant with this decrease in input power, PPF decreased by 60% in HPS and 50% in MH. The HPS lamp has characteristic spectral peaks at 589 and 595 nm. As power to the HPS lamps was decreased, the 589-nm peak remained constant while the 595-nm peak decreased, equaling the 589-nm peak at 345-W input, and the 589-nm peak was almost absent at 270-W input. The MH lamp has a broader spectral output but also has a peak at 589 nm and another smaller peak at 545 nm. As input power to the MH lamps decreased, the peak at 589 diminished to equal the 545-nm peak. As input power approached 428 W, the 589-nm peak shifted to 570 nm. While the spectrum changed as input power was decreased in the MH and HPS lamps, the phytochrome equilibrium ratio (Pfr: Ptot) remains unchanged for both lamp types.
Electronic dimming of high intensity discharge lamps offers control of photosynthetic photon flux (PPF) but is often characterized as causing significant spectral changes. Growth chambers with 400 W metal halide (MH) and high pressure sodium (HPS) lamps were equipped with a dimmer system using silicon controlled rectifiers (SCR) as high speed switches. Phase control operation turned the line power off for some period of the AC cycle. At full power the electrical input to HPS and MH lamps was 480 W (RMS) and could be decreased to 267 W and 428 W, respectively, before the arc was extinguished. Concomitant with this decrease in input power, PPF decreased by 60% in HPS and 50% in MH. The HPS lamp has characteristic spectral peaks at 589 and 595 nm. As power to the HPS lamps was decreased the 589 nm peak remained constant while the 595 nm peak decreased, equalling the 589 nm peak at 345 W input, and was almost absent at 270 W input. The MH lamp has a broader spectral output but also has a peak at 589 nm and another, smaller peak, at 545 nm. As input power to the MH lamps decreased the 589 nm peak diminished to equal the 545 nm peak. As input power approached 428 W the 589 nm peak shifted to 570 nm. While a spectral change was observed as input power was decreased in both MH and HPS lamps, the phytochrome equilibrium ratio (Pfr/Ptot) remain unchanged for both lamp types.
Abstract
Net photosynthesis (Pn), transpiration (Tr), and stomatal conductance for CO2 (gs) were determined at 26° ± 1°C for leaves on intact and excised apple shoots at different vapor pressure gradients (VPG’s). Pn, Tr, and gs of leaves on intact and excised shoots responded similarly to changes in VPG. Pn and gs were not affected directly by VPG. Tr increased as VPG increased since stomatal closure did not counterbalance the increased VPG.