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Oscar Monje, Sylvia Anderson and Gary W. Stutte

surface ( McMaster et al., 2003 ). Several studies have examined root zone temperature (RZT) effects in lettuce ( Lactuca sativa L.) ( He et al., 2001 ), wheat ( Guedira and Paulsen, 2002 ; Kirkham and Ahring, 1978 ), and creeping bentgrass ( Agrostis

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Catherine A. Neal

AGS production systems and to monitor root-zone temperatures (RZTs) to answer the following questions for northern New England and similar cold climates: Is growth enhanced in PiP or other modified container systems as compared with traditional

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Stephen S. Deschamps and Shinsuke Agehara

under more reflective mulch types are consistent with these previous observations. Fig. 2. ( A ) Average hourly root-zone temperatures at a 10-cm depth for the bed center and bed shoulder. ( B ) Tables showing the number of hours of statistically

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W. Garrett Owen and Roberto G. Lopez

.6 ± 8.1 or 120.4 ± 5.8 μmol·m −2 ·s −1 or 88.3 ± 5.3 or 121.2 ± 4.7 μmol·m −2 ·s −1 , respectively, delivered from high-pressure sodium lamps from 0600 to 2200 hr . Root-zone temperature set points were 21, 23, 25, and 27 °C. Growth and morphological

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William J. Foster, Dewayne L. Ingram and Terril A. Nell

Rooted stem cuttings of Ilex crenata Thunb. `Rotundifolia' were grown in a controlled-environment growth chamber. Root-zone temperatures were controlled with an electric system. Shoot carbon exchange and root respiration rates were determined in response to root-zone temperatures of 28, 32, 36, and 40C for 6 hour·day–1 for 7 days. Photosynthesis was decreased by root zones ≥ 32C, while root respiration increased with increasing root-zone temperature. Decreased photosynthetic rates were not due to increased stomatal resistance.

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Beth Jez Lawrence and Jayne M. Zajicek

Sap flow rates of three Cercis spp. exposed to supraoptimal root-zone temperatures were characterized in a controlled environment chamber using a water bath to control temperatures. Flow rates of sap in the xylem were measured every 15 sec. and averaged over 15 min. intervals. Sap flow measurements were correlated to root-zone temperatures recorded during the same time intervals. Whole plant transpiration was measured gravimetrically. Root-zone temperatures were maintained at 22C for three consecutive 24-hr cycles and then increased to 45C for an additional three 24-hr periods. All plants, regardless of species, had reduced sap flow patterns when exposed to high root-zone temperatures. Plants maintained at a constant temperature of 22C showed no extreme fluctuations in sap flow rate. Stomatal conductance rates and leaf water potentials showed similar trends to whole plant transpiration.

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Khin San Wai and S.E. Newman

The response of Antirrhinum majus (snapdragon) cultivars (`Tampicoi' and `Rainier White') to night air temperatures (10C and 20C) and elevated root-zone temperature (26C and ambient) was studied. Height of plants grown with a heated root-zone were greater, compared to unheated at both night temperatures for both cultivars. Shoot dry weight of `Tampico' plants was reduced by heated root-zone temperature at 20C night air temperature. Raceme length was greater with heated root-zone temperature compared to unheated at 10C night air temperature. Days to flower were shorter with heated compared to unheated root-zone at both night air temperatures for both cultivars. Stomatal diffusive resistance was greater on plants with unheated compared to heated root-zone temperature at 10C night air temperature for `Rainier White'.

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John M. Ruter and Dewayne L. Ingram

Plants of `Rotundifolia' holly (Ilex crenata Thunb.) were grown for 3 weeks with root zones at 30,34,38, or 42C for 6 hours daily to evaluate the effects of supraoptimal root-zone temperatures on various photosynthetic processes. After 3 weeks, photosynthesis of plants grown with root zones at 38 or 42C was below that of plants grown at 30 or 34C. Chlorophyll and carotenoid levels decreased while leaf soluble protein levels increased as root-zone temperature increased. Ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBisCO) activity per unit protein and per unit chlorophyll responded quadratically, while RuBisCO activity per unit fresh weight increased linearly in response to increasing root-zone temperature. Results of this study suggest that `Rotundifolia' holly was capable of altering metabolism or redistributing available assimilates to maintain CO2 assimilation rates in response to increasing root-zone temperatures.

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Khin San Wai and Steven E. Newman

Growth chamber studies using elevated root-zone temperatures and greenhouse studies using two root-zone and two night air temperatures were conducted to determine the effects on growth and flowering of two response groups [`Rainier White' (Group II) and `Tampico' (Group III)] of cut-flower snapdragons (Antirrhinum majus L.). Chamber-grown snapdragons with the root zone at 30C had shorter stems and a lower dry weight than those at 20C. Holding the root zone above 26C increased time to flower. Greenhouse-grown `Tampico' and `Rainier White' snapdragon stems were longer with increased root-zone temperature regardless of night air temperature. Time to flower was reduced an average of 6 days with increased root-zone temperature and 12 days when the night air was maintained at 20C. This study demonstrated that the effects of relatively low greenhouse temperatures may be offset by root-zone heat.

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G.W. Stutte, N.C. Yorio, C.L. Mackowiak and R.M. Wheeler

This experiment was performed to test the hypothesis that tuber formation in potato is inhibited by short-term increases in root-zone temperature. Micro-propagated potato cv. Norland plantlets were grown in recirculating nutrient film culture under daylight fluorescent lamps at 350 μmol·m–2·s–1 PPF with at 20/16°C thermocycle at 1200 μmol·mol–1 CO2 under inductive (12-hr light/12-hr dark) or non-inductive (12-hr light/12-hr dark with a 15-min light break 6 hr into the cycle) photoperiods for 42 days. Root-zone treatments consisted of continuous 18°C, continuous 24°C, 18°C with a 24°C cycle between 14 and 21 DAP (prior to tuber initiation), and 18°C with a 24°C cycle between 21 and 28 DAP (during the period of tuber initiation). The root-zone temperature was maintained with a recirculating, temperature-controlled, heat-exchange coil submerged in each nutrient solution. Warm root-zone temperatures did not inhibit tuber formation under an inductive photoperiod. The non-inductive photoperiod resulted in a 65% reduction in tuber biomass compared to the inductive photoperiod. Continuous 24°C and exposure to 24°C prior to tuber initiation reduced tuber formation an additional 40% under the non-inductive photoperiod. Both continuous and transient 24°C root-zone temperatures increased biomass partitioning to root/stolons compared to the 18°C treatment under both photoperiods. Total plant biomass was highest in plants exposed to continuous 24°C under both photoperiods. Results suggest that transient episodes of warm (24°C) root-zone temperature do not inhibit tuber formation in potato under inductive photoperiods. However, transient episodes of warm (24°C) root-zone temperatures did interact with stage of development under the non-inductive photoperiod.