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Hans-Peter Kläring and Angela Schmidt

( Marcelis and Baan Hofman-Eijer, 1993 ). Nevertheless, reports show that cucumber can be grown successfully at low night temperatures of 11–14 °C ( Heißner and Drews, 1986 ). One reason for this phenomenon could be that diurnal temperature variations have an

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M.P.N. Gent and Y.-Z. Ma

Does heating roots only in the day improve growth and nutrient status of seedlings grown under a day-to-night difference (DIF) in air temperature? To answer this question, tomato seedlings (Lycopersicon esculentum Mill) were grown in early March or April in greenhouses heated to give either a 14 °C DIF or a 5 °C DIF with a 18 °C mean. The roots were in peat-vermiculite medium that was unheated or heated to 21 °C, constantly or only in the day, or only in the night. Growth was faster and there were higher concentrations of elements in leaves under 5 °C compared to 14 °C air DIF. Any root-zone heating increased growth and nutrition compared to no heating. Under both air conditions, the trend in root temperature treatments was constant > day > night. In general, there was no benefit of heating the roots only in the day, compared to constant heating of the root zone, even with a large diurnal variation in temperature of the shoot. The only nutrient to respond differently to root heating under 5 °C compared to 14 °C air DIF was nitrate in leaves. Under a 14 °C air DIF, heating roots in the day resulted in the highest nitrate concentration, whereas constant root heating was optimal under a 5 °C DIF. Research supported in part by grant 93-37100-9101 from NRI Competitive grants program/USDA.

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Martin P.N. Gent

temperature, respectively. Diurnal variation of metabolites in spinach. When harvested at 3-h intervals in 2010, the dry/fresh mass ratio of spinach shoots varied with time of day from 91 to 114 g·kg −1 ( Table 3 ). First-, second-, and third-order terms in

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Brunella Morandi, Luigi Manfrini, Marco Zibordi, Massimo Noferini, Giovanni Fiori, and Luca Corelli Grappadelli

diameter variations over time, based on a low-cost linear potentiometer. The sensor is described, and data on the signal stability over a range of temperatures and from an actual study of fruit growth physiology are provided as a example of the potential of

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Gang-Yi Wu, Jun-Ai Hui, Zai-Hua Wang, Jie Li, and Qing-Sheng Ye

−2 ·s −1 ( Fig. 2C ). The P n decreased when temperature was over 30 °C, indicating that the optimum temperatures for Dendrobium photosynthesis were in the range of 26 to 30 °C. P n diurnal and annual variation of the four Dendrobium species

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Mark A. Rose and John W. White

Temperature affects all major plant physiological processes. Traditional methods of controlling greenhouse temperatures use aerial sensors that do not monitor temperatures within each component of the soil-plant-atmosphere continuum.

Bench, pot, plant canopy, and aerial temperatures were monitored using thermocouples and thermistors processed by environmental computers during a wide range of greenhouse conditions. These include diurnal cycles of high and low solar radiation, night periods with and without artificial lighting, and various ventilation and heating conditions. Spatial temperature gradients of 10-22 °C were discovered during both day and night conditions. These spatial variations cause significant differences in average temperatures between and within benches over diurnal and even seasonal cycles.

Preliminary surveys of microclimatic variations that occur within the greenhouse experimental area are essential for choosing the proper experimental design. Continuous environmental monitoring during the experiment is necessary for interpreting experimental results.

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Helen H. Taylor, Robert L. Mikkelsen, and Stuart L. Warren

The N release patterns of composted turkey litter, composted yard waste, and composted municipal waste amended pine bark substrates were measured under simulated diurnal temperature variations [25C, 45C, and 45/25C (14/10 h)] found in container substrates. Temperature regime, compost, and the interaction between temperature and compost affected the NH4 and NO3 availability and the total N released from the composted waste products over the 16-week experiment. Within each temperature regime, the composted turkey litter released greater amounts of NH4 and more total inorganic N than the municipal and yard wastes. The turkey litter yielded the highest NO3 concentrations at 25C, while the municipal waste produced the highest NO3 concentrations at the 45C and the 45/25C temperatures. Temperatures higher than 25C inhibited nitrification in the turkey litter-amended substrates; however, the 45C and the 45/25C treatments resulted in greater total N mineralization than the 25C treatment.

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J.J. Steiner and K. Opoku-Boateng

Abbreviations: ACF, autocorrelation function; AHT, average houly temperature; GERM, percentage germination; HT, maximum temperature; NOS, number of seeds per inflorescence; LT, minimum temperature nd, normal difference; PACF, partial autocorrelation

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J.W. White, H. Chen, X. Zhang, D.J. Beattie, and H. Grossman

Floral initiation and development of greenhouse and growth room-grown Aquilegia × hybrida Sims cultivars were studied using a scanning electron microscope. All greenhouse-grown cultivars initiated floral buds before cold treatment, ≈ 5 months after sowing. Floral initiation occurred at the apical meristem and proceeded acropetally on an elongated conical axis in the sequence: sepals, petals, stamens, stamenodia, and carpels. In a second experiment, 13 Aquilegia cultivars, three of which had been used in the first experiment, were grown as seedlings in a growth room at 20C under an 8-, 12-, 16-, or 20-hr photoperiod, each totaling 10.2 mol·day-1·m-2 irradiance from cool-white fluorescent lamps. Here, floral initiation was absent even after 7 months from sowing, presumably because there was no diurnal variation in irradiance or temperature.

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Keith A. Funnell, Errol W. Hewett, Julie A. Plummer, and Ian J. Warrington

Photosynthetic activity of individual leaves of Zantedeschia Spreng. `Best Gold' aff. Z. pentlandii (Wats.) Wittm. [syn. Richardia pentlandii Wats.] (`Best Gold'), were quantified with leaf expansion and diurnally, under a range of temperature and photosynthetic photon flux (PPF) regimes. Predictive models incorporating PPF, day temperature, and percentage leaf area expansion accounted for 78% and 81% of variation in net photosynthetic rate (Pn) before, and postattainment of, 75% maximum leaf area, respectively. Minimal changes in Pn occurred during the photoperiod when environmental conditions were stable. Maximum Pn (10.9μmol·m-2·s-1 or 13.3 μmol·g-1·s-1) occurred for plants grown under high PPF (694 μmol·m-2·s-1) and day temperature (28 °C). Acclimation of Pn was less than complete, with any gain through a greater light-saturated photosynthetic rate (Pmax) at high PPF also resulting in a reduction in quantum yield. Similarly, any gain in acclimation through increased quantum yield under low PPF occurred concurrently with reduced Pmax. It was concluded that Zantedeschia `Best Gold' is a shade tolerant selection, adapted to optimize photosynthetic rate under the climate of its natural habitat, by not having obligate adaptation to sun or shade habitats.