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Jeffrey C. Stark, Joseph J. Pavek, and Ian R. McCann

Abbreviations: DSI, drought susceptibility index; ET, evapotranspiration; AT, canopy - air temperature; VPD, vapor pressure deficit. 1 Associate Professor, Dept. of Plant, Soil and Entomological Sciences. 2 Research Geneticist, U.S. Dept. of

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Alexandra Boini, Enrico Muzzi, Aude Tixier, Maciej Zwieniecki, Luigi Manfrini, and Luca Corelli Grappadelli

et al., 2019 ) in the shoots and is followed by translocation to the buds ( Bonhomme et al., 2010 ; Lacointe et al., 2004 ). In fact, trees respond to root-to-canopy temperature gradients by changing their local nonsoluble carbohydrate management and

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Yiwei Jiang, Huifen Liu, and Van Cline

( Jiang and Carrow, 2007 ). Responses of turfgrass to water deficit conditions can also be assessed by leaf or canopy temperature. Leaf temperature will be greater than ambient temperature when grasses are under drought stress as a result of reduced

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Bernadine C. Strik, Amanda J. Davis, David R. Bryla, and Scott T. Orr

black, white, and green. White weed mat reflects light into the plant canopy, which reduces the soil temperature and influences the fruit quality of apple and blackberry ( Rubus L. subgenus Rubus , Watson) ( Funke and Blanke, 2005 ; Makus, 2007

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Richard J. McAvoy

Root-zone and plant canopy temperatures were continuously monitored as a poinsettia (Euphorbia pulcherrima Willd. ex JSI.) crop was grown in the greenhouse under warm day/cool night [(+) DT-NT] or cool day/warm night [(-) DT-NT] temperature regimes. Day temperatures were imposed from 0900 to 1700 hr. Light levels photosynthetic photon flux (PPF) and outside ambient air temperatures were also monitored. Temperature differences between the root-zone and plant canopy microenvironments were most extreme during the night-to-day and day-to-night temperature transition periods. The temperature difference between the plant canopy and the root zone following temperature transition periods had been previously identified as a critical factor affecting stem elongation. Overall poinsettia height was consistently shorter under the (-) DT-NT than under the (+) DT-NT environment.

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

Abbreviations: A, alfalfa; CWSI, crop water stress index; CTV, canopy-temperature-variability; D, drainage; ET, evapotranspiration; FI, full irrigation; H, herbicide strip; I, irrigation, IR, infrared P, black plastic mulch; R n , net radiation; SDD

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Matthew D. Whiting and Gregory A. Lang

To initiate photosynthetic studies of sweet cherry (Prunus avium L.) canopy architectures and cropping management under high light and temperature conditions (Yakima Valley, Wash.), we developed a whole-canopy research cuvette system with a variable airflow plenum that allowed different patterns of air delivery (in concentric circles around the trunk) into the cuvette. Air and leaf temperatures (Tair and Tleaf, respectively) were determined at four horizontal planes and four directional quadrants inside cuvette-enclosed canopies trained to a multiple leader/open-bush or a multiple leader/trellised palmette architecture. Air flow rate, air delivery pattern, and canopy architecture each influenced the whole-canopy temperature profile and net CO2 exchange rate (NCER) estimates based on CO2 differentials (inlet-outlet). In general, Tair and Tleaf were warmer (≈0 to 4 °C) in the palmette canopy and were negatively correlated with flow rate. The response of Tair and Tleaf to flow rate varied with canopy position and air delivery pattern. At a flow of 40 kL·min-1 (≈2 cuvette volume exchanges/min), mean Tair and Tleaf values were 2 to 3 °C warmer than ambient air temperature, and CO2 differentials were 15-20 μL·L-1. Tair and Tleaf were warmer than those in unenclosed canopies and increased with height in the canopy. Carbon differentials declined with increasing flow rate, and were greater in the palmette canopy and with a less dispersed (centralized) delivery. Dispersing inlet air delivery produced more consistent values of Tair and Tleaf in different canopy architectures. Such systematic factors must be taken into account when designing studies to compare the effects of tree architecture on whole-canopy photosynthesis.

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D.G. Mortley, J.H. Hill, C.K. Bonsi, W.A. Hill, and C.E. Morris

Growth chamber studies were conducted to determine if inverse day/night temperature could control canopy height of sweetpotato without adversely affecting storage root yield. Four 15-cm-long vine cuttings of TU-82-155 sweetpotato were grown in rectangular nutrient film technique hydroponic troughs for 120 days. Two troughs were placed into each of six reach-in growth chambers and subjected to 24/18, 26/20, 28/22, 18/24, 20/26, and 22/28 °C, respectively. Growth chamber conditions included a 12/12-h photoperiod, 70% RH, and photosynthetic photon flux of 1000 μmol·m-2·s-1 at canopy level. Total and edible storage root yields were reduced by 50% among plants grown under cool days/warm nights regimes. Harvest index was similar among treatments except for the low value obtained at 22/28 °C. Canopy height was positively correlated with the change in temperature, and for every 2 °C decrease there was a 3.1 centimeter decrease in canopy height. Inverse day/night temperature effectively controlled canopy height but at the expense of storage root production.

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Nita A. Davidson, L. Theodore Wilson, Michael P. Hoffmann, and Frank G. Zalom

Abbreviations: AIR, above the soil surface; IN, inside the plant canopy; TOP, top surface of the plant canopy. 1 Dept. of Entomology, Texas A&M Univ., College Station, TX 77843. 2 Dept. of Entomology, Cornell University, Ithaca, NY 14853. We thank

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Alvaro Otero, Carmen Goni, and Jim Syvertsen*

Six-year-old `Spring' navel [Citrus sinensis (L.). Osb.] orange trees were either totally defruited, 50% defruited or left fully cropped to study effects of fruit load on growth net gas exchange characteristics of mature leaves on seven selected clear days from Nov. 2001 through July 2002. Near harvest time, defruited trees had more shoot flushes, greater leaf dry wt per area (LDW/A) but lower net assimilation of CO2 (Ac) and stomatal conductance (gs) at midday than leaves on trees with fruit. Defruited trees had a higher ratio of internal to ambient CO2 (Ci/Ca) concentration in leaves implying internal limitations were dominant over stomatal limitation on Ac. Removal of half the crop increased individual fruit mass but reduced fruit color development. Half the trees were also shaded for four months prior to harvest with reflective 50% shade cloth to determine effects of lower leaf temperature (Tl) and leaf-to-air vapor pressure difference (D) on leaf responses. On selected clear days throughout the season, shade increased midday Ac and gs but decreased Ci/Ca compared to trees in the open implying that high mesophyll temperatures in sunlit leaves were more important than gs in limiting Ac. There were no effects of the shade treatment on canopy volume, yield or fruit size. Shaded fruit developed better external color but lower Brix than sun-exposed fruit. Thus, the presence of mature fruit maintained higher Ac than in leaves on defruited trees but high leaf temperatures and D reduced gs and Ac on warm days throughout the season.