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Grete Waaseth, Roar Moe, Royal D. Heins, and Svein O. Grimstad

Varying photothermal ratios (PTR) were supplied to Salvia ×superba Stapf `Blaukönigin' during pre-inductive vegetative development with the exception of a short germination period under uniform conditions. In addition, both unvernalized plants and plants receiving a saturating vernalization treatment of 6 weeks at 5 °C were given two photosynthetic photon flux (PPF) levels (50 or 200 μmol·m-2·s-1) during subsequent inductive 16-hour long days. There were no effects of PTR treatments during vegetative development on subsequent flowering. However, the higher PPF level during inductive long days significantly accelerated floral evocation in unvernalized plants, lowering the leaf number at flowering. The effect was practically negligent after the vernalization requirement was saturated. In a second experiment, varying periods (4, 7, 10, and 14 days or until anthesis) at a PPF of 200 μmol·m-2·s-1 during 20-hour days were given at the beginning of a long-day treatment, either with or without preceding vernalization treatment. Flowering percentage increased considerably as the period at 200 μmol·m-2·s-1 was extended compared with plants grown at a lower PPF of 50 μmol·m-2·s-1. However, the leaf number on flowering plants was not affected, except in unvernalized plants receiving the highest PPF continuously until anthesis, where leaf number was reduced by almost 50%. We propose that the PPF-dependent flowering is facilitated either by the rate of ongoing assimilation or rapid mobilization of stored carbohydrates at the time of evocation. Abortion of floral primordia under the lower PPF (50 μmol·m-2·s-1) irrespective of vernalization treatment indicates that the assimilate requirement for flower bud development is independent of the mechanism for floral evocation.

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D. Schwarz, H.-P. Kläring, M.W. van Iersel, and K.T. Ingram

An increase in nutrient solution concentration to produce high-quality fruit vegetables, such as tomatoes, may reduce growth and yield. One reason might be inhibition of photosynthesis, but results of photosynthesis studies in the literature are inconsistent. In this study, we investigated growth and photosynthesis of whole `Celebrity' and `Counter' tomato [Lycopersicon esculentum (L.) Mill.] plants in response to nutrient solution concentration, measured as electrical conductivity (EC). The effects of two levels of photosynthetic photon flux density (PPF = 400 or 625 μmol·m-2·s-1) on plant response to nutrient solution EC in a range between 1.25 to 8.75 dS·m-1 in a series of four experiments in gas exchange chambers placed in larger growth chambers were examined. Increasing PPF enhanced tomato growth and photosynthesis but increasing EC diminished them. Reduction of dry weight was 1.9% to 7.3%, while plant photosynthesis was reduced between 1.7% and 4.5% for each 1 dS·m-1. Increasing EC did not decrease dry matter content and leaf photosynthesis. Mean plant dry matter content ranged between 70 and 95 g·kg-1, and net leaf photosynthesis on the last measurement day was between 7.5 and 11.3 μmol·m-2·s-1, depending on experiment. The decrease in whole plant photosynthesis with an increase in EC was caused by decreased leaf area but not by a decrease in leaf photosynthesis.

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Marc W. van Iersel and David Gianino

providing supplemental lighting. These lights are expensive to use. Combining the ballast and bulb, a single 400-W HPS light consumes ≈465 W of electrical energy ( Nelson, 2003 ). To provide supplemental light at a PPF of ≈85 μmol·m −2 ·s −1 requires

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James E. Faust and Royal D. Heins

* Professor of Horticulture. Abbreviations: LUR, leaf unfolding rate; PPF, photosynthetic photon flux. 1 Graduate Research Assistant. We acknowledge the support of the Michigan Agricultural Experiment Station and Express Seed Co., Oberlin, Ohio

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Carl E. Niedziela Jr., Mary A. Depa, Paul V. Nelson, Daniel H. Willits, Mary M. Peet, David A. Dickey, and Nancy C. Mingis

other species grown under high levels of CO 2 ( Knecht and O’Leary, 1983 ; Patterson and Flint, 1982 ; Sionit et al., 1981 ). Similarly, an increase in PPF also yields improved growth and greater nutrient demand ( Taiz and Zeiger, 2010 ). Frantz

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Jongyun Kim, Seung Won Kang, Chun Ho Pak, and Mi Seon Kim

factor for plant growth is reduced light intensity ( Manaker, 1997 ). Although the light intensity outdoor is generally higher than 1000 μmol·m −2 ·s −1 of PPF at sunny days, typical indoor light intensity is less than 40 μmol·m −2 ·s −1 ( Manaker

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Amy L. Burton, Svoboda V. Pennisi, and Marc W. van Iersel

material, growers need production guidelines for irradiance, temperature, and nutrition regimes, as well as growth control. The majority of tropical foliage plants are produced for use indoors. Generally, photosynthetic photon flux ( PPF ) in postharvest

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Woei-Jiun Guo, Yu-Zu Lin, and Nean Lee

impacts of light intensity and duration on photosynthetic ability in a Phalaenopsis leaf are not well established. A Phalaenopsis hybrid demonstrated that the net daily CO 2 assimilation will saturate at 130 μmol·m −2 ·s −1 PPF ( Ota et al., 1991

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David F. Graper and Will Healy

Abbreviations: DW, dry weight; FW, fresh weight; HPS, high pressure sodium; IR, infrared; PPF, photosynthetic photon flux; RGR, relative growth rate. 1 Currently Assistant Professor, Dept. of Horticulture, Forestry, Landscape and Parks, South Dakota

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Charles Barnes, Theodore Tibbitts, John Sager, Gerald Deitzer, David Bubenheim, Gus Koerner, and Bruce Bugbee

PPF sensor with identical specifications and a similar spectral response to the LI-CORPPF sensor, but, unfortunately, we were notable to include the Skye PPF sensor in this study, The cost of publishing this paper was defrayed in part by the payment of