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Timothy K. Broschat

Royal palms [Roystonea regia (HBK.) O.F. Cook], coconut palms (Cocos nucifera L. `Malayan Dwarf'), queen palms [Syagrus romanzoffiana (Chamisso) Glassman], and pygmy date palms (Phoenix roebelenii O'Brien) were grown in a rhizotron to determine the patterns of root and shoot growth over a 2-year period. Roots and shoots of all four species of palms grew throughout the year, but both root and shoot growth rates were positively correlated with air and soil temperature for all but the pygmy date palms. Growth of primary roots in all four species was finite for these juvenile palms and lasted for only 5 weeks in royal palms, but ≈7 weeks in the other three species. Elongation of secondary roots lasted for only 9 weeks for coconut palms and less than half of that time for the other three species. Primary root growth rate varied from 16 mm·week-1 for coconut and pygmy date palms to 31 mm·week-1 for royal palms, while secondary root growth rates were close to 10 mm·week-1 for all species. About 25% of the total number of primary roots in these palms grew in contact with the rhizotron window, allowing the prediction of the total root number and length from the sample of roots visible in the rhizotron. Results indicated that there is no obvious season when palms should not be transplanted in southern Florida because of root inactivity.

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Rik van Gorsel, A. Verlind, A. van de Wiel, and G. van Leeuwen

Low root zone temperatures in summer stimulate generative development of Alstroemeria, resulting in a higher flower production in winter. The effects of greenhouse soil and air temperatures on vase life and ornamental value were evaluated. Preharvest treatments were two locations (field stations), four air temperatures (9, 12, 15, 18C), four root zone temperatures (11, 14, 17C, uncontrolled) and three varieties ('Flamengo', 'Jubilee', 'Wilhelmina') in a factorial design. The flowers were placed in a commercial pretreatment solution for 24 hours immediately after harvest. After a two day transport simulation and rehydration for 3 hours at 5C, flowers were kept at 1.5 W.m-2 PAR (12hr/day), 20C and 60% RH. The experiment was done three times. Results from the first harvest showed that lowering the soil temperature increased the number of stems that had two whirls of flowers opening after harvest. Average vase life was two weeks. Low air temperatures increased whirl opening as well, and increased vase life by one or two days. Ornamental value and number of flower branches per stem were not affected.

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David C. Percival, John T.A. Proctor, and M.J. Tsujita

The influence of irradiance, CO2, and temperature on whole-plant net C exchange rate (NCER) of micropropagated raspberries (Rubus idaeus L. cv. `Heritage') was examined in 1994. Irradiances >1000 μmolm–2–s–1 PAR were required for light saturation, and net photosynthesis (Pn) greatly increased under CO2 enrichment (up to 2000 μlliter–1) and was optimum at 17C. Temperature effects were separated in another experiment using varying air and soil temperatures (15, 20, 25, 30, and 35C) under saturated light and ambient CO2 levels (350 μlliter–1). Both air and soil temperature influenced net Pn, with maximum rates occurring at an air/soil temperature of 17/25C and each contributing 71.2% and 26.7%, respectively, to the total variation explained by a polynomial model (R 2 = 0.96). Dark respiration and root respiration rates also increased significantly with elevated air and soil temperatures. Therefore, results from this study indicate that maximum net Pn occurred at an air/soil temperature of 17/25C and that irradiance, CO2 levels, and shoot and root temperatures are all important factors in examining NCER in raspberries.

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B. Todd Bunnell, Lambert B. McCarty, and Hoke S. Hill

Creeping bentgrass (Agrostis palustris Huds.) is used on putting greens for its fine-leaf texture, consistent speed, smooth ball roll, and year-round color. In recent years bentgrass use has extended into the warmer climates of the southern United States. Being a C3 plant, bentgrass is not well adapted to extended hot and humid environmental conditions. Subsurface air movement systems are now commercially available that can transport air through the root zone to alter soil conditions and potentially improve bentgrass survival. This research investigated the effects of subsurface air movement on the composition of soil gases, matric potential, temperature, and growth response of a sand-based creeping bentgrass golf green. Treatments included: air movement direction (evacuate, inject, and no air) and duration of air movement (0400-0600 hr, 1000-1800 hr, and 24 hours). Treatment combinations were imposed for 13 days. Subsurface air movement reduced CO2 at the 9-cm depth to values <0.0033 mol·mol-1 when evacuating or injecting air, depending upon duration. Soil matric potentials at a 9-cm depth were decreased by a maximum of 96% when evacuating air for 24-hour duration compared to no-air plots. Soil temperatures at 9 cm were decreased ≈1 to 1.5 °C when injecting air from 1000 to 1800 hr and 24-hour treatments and increased ≈0.75 °C when evacuating air from 1000 to 1800 hr. Subsurface air movement did not improve creeping bentgrass turf quality or rooting. Although not effective in improving the growth response of creeping bentgrass, subsurface air movement may be a useful tool to improve soil gas composition, reduce excess soil moisture, and potentially reduce soil temperature(s) of heat-stressed creeping bentgrass golf greens.

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Timothy K. Broschat

Royal palms [Roystonea regia (HBK.) O.F. Cook], coconut palms (Cocos nucifera L. `Malayan Dwarf'), queen palms [Syagrus romanzoffiana (Chamisso) Glassman], and pygmy date palms (Phoenix roebelenii O'Brien) were grown in a rhizotron to determine the patterns of root and shoot growth over a 2-year period. Roots and shoots of all four species of palms grew throughout the year, but both root and shoot growth rates were positively correlated with air and soil temperature for all but the pygmy date palms. Growth of primary roots in all four species was finite for these juvenile palms and lasted for only 5 weeks in royal palms, but ≈7 weeks in the other three species. Elongation of secondary roots lasted for only 9 weeks for coconut palms and less than half of that time for the other three species. Primary root growth rate varied from 16 mm·week-1 for coconut and pygmy date palms to 31 mm·week-1 for royal palms, while secondary root growth rates were close to 10 mm·week-1 for all species. About 25% of the total number of primary roots in these palms grew in contact with the rhizotron window, allowing the prediction of the total root number and length from the sample of roots visible in the rhizotron. Results indicated that there is no obvious season when palms should not be transplanted in southern Florida because of root inactivity.

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Fahrurrozi Aziz, Katrine A. Stewart, and Sylvie Jenni

1 Former PhD student. Present address: Fakultas Pertanian Universitas Bengkulu, Jalan Raya Kandang Limun Bengkulu, 38371A Indonesia. 3 Researcher. We thank D.L. Smith of McGill University for reviewing this manuscript and use of laboratory equipment

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Preston K. Andrews, David J. Chalmers, and Mapasaka Moremong

, stress-degree-day; SW, short wave; TSD, temperature-stress-day; VPD, vapor pressure deficit; WI, withheld irrigation. 1 Postdoctoral Fellow. Current address: Dept. of Horticulture and Landscape Architecture, Washington State Univ., Pullman, WA 99164

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Dan Drost, Taunya Ernst, and Brent Black

temperature range for longer period each day, thereby improving growth rates and reducing low temperature–related stresses. However, during the winter, cold air and soil temperatures as well as seasonal changes in light levels become the main limiting factors

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Hans Christian Wien

than in soil temperature ( Fig. 4 ). Although outside air temperatures averaged over 4 d did not rise higher than –4 °C, they reached +5 °C inside the tunnel. In contrast, the soil temperature at 10-cm depth fluctuated little and was only 2 °C higher

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Shigeoki Moritani, Hirotada Nanjo, Atsushi Itou, and Teruki Imai

observable variations were seen to occur between 1:00 pm and 4:00 pm . The slow increase and decrease in soil temperatures after sunrise and solar noon, respectively, led to creation of an ellipsoidal diurnal relationship between greenhouse air and media