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Medani Omer, James C. Locke, and Jonathan M. Frantz

., 1987 ). Therefore, leaf temperature is a potentially sensitive indicator of plant moisture stress. Using a simplified energy balance model ( Monteith, 1977 ), a sensitivity analysis of leaf temperature and transpiration can be performed. Assuming some

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J.H. Lieth and C.C. Pasian

A mathematical description for the relationship between the rate of rose (Rosa hybrida L.) leaf net photosynthesis and photosynthetically active radiation, leaf temperature, and leaf age is developed. The model provides a tool for the prediction of these rates for leaves growing in a rose crop canopy.

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Jieshan Cheng, Peige Fan, Zhenchang Liang, Yanqiu Wang, Ning Niu, Weidong Li, and Shaohua Li

significant differences in E between “+ fruit” and the two “bag removal” treatments ( Fig. 1C ). Fig. 1. ( A ) Diurnal net photosynthetic rate (P n ), ( B ) stomatal conductance ( g s ), ( C ) transpiration (E), ( D ) leaf temperature (T leaf ) and

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William L. Bauerle and Joseph D. Bowden

hypothesis that variation in L w within red maple considerably modified boundary layer conductance, leaf temperature, and transpiration aside from physiological differences. MATERIALS AND METHODS Site and plant material. Measurements were taken on South

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Ved Parkash and Sukhbir Singh

stress, such as decreased enzyme activity, protein synthesis, CO 2 assimilation, g S , leaf water status and efficiency of photosystem II, and increased leaf temperature ( Behboudian et al., 1986 ; García-Legaz et al., 1993 ; Munns, 2002 ). Ionic

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Joseph Masabni, Youping Sun, Genhua Niu, and Priscilla Del Valle

microclimate in the summer by decreasing leaf temperature and leaf transpiration rate, thus alleviating heat stress ( Aberkani et al., 2008 ). The cultivation area under shade is constantly increasing in Mediterranean countries such as Israel, Morocco, and

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Oliver Körner, Jesper Mazanti Aaslyng, Andrea Utoft Andreassen, and Niels Holst

, i.e., condensation on the plant surface and an increasing risk of diseases ( Fig. 3 ). The effects of short-wave radiation on both leaf temperature and dew formation (i.e., negative λE) decreased with increasing LAI ( Figs. 3 and 4 ). Those effects

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John L. Jifon and James P. Syvertsen

Effects of foliar sprays of a kaolin clay particle film (Surround WP) on leaf temperature (Tlf), net gas exchange, chlorophyll fluorescence and water relations of sun-exposed leaves on field-grown grapefruit trees (Citrus paradisi L.) were studied during Summer and Fall 2001. Trees were sprayed twice a week for 3 weeks with aqueous suspensions of kaolin (Surround) at 60 g·L-1. Physiological effects of kaolin application were most prominent around midday on warm sunny days than in mornings, evenings or cloudy days. Kaolin sprays increased leaf whiteness (62%), reduced midday leaf temperature (Tlf; ≈3 °C) and leaf to air vapor pressure differences (VPD; ≈20%) compared to water-sprayed control leaves. Midday reductions in Tlf and VPD were accompanied by increased stomatal conductance (gs) and net CO2 assimilation rates (ACO2) of kaolin sprayed leaves, suggesting that gs might have limited ACO2 in water-sprayed control leaves. Midday photoinhibition of photosynthesis was 30% lower in kaolin-sprayed leaves than in control leaves. Midday water use efficiency (WUE) of kaolin-sprayed leaves was 25% higher than that of control leaves. However, leaf transpiration and whole-tree water use were not affected by kaolin film sprays. Increased WUE was therefore, due to higher ACO2. Leaf intercellular CO2 partial pressures (Ci) were similar in control and kaolin-sprayed leaves indicating that stomatal conductance was not the major cause of reduced ACO2. These results demonstrate that kaolin sprays could potentially increase grapefruit leaf carbon uptake efficiency under high radiation and temperature stress.

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Mark A. Rose, David J. Beattie, and John W. White

Two distinct patterns of whole-plant transpiration (WPT) were observed in `Moonlight' rose (Rosa hybrida L.) using an automated system that integrated a greenhouse climate computer, a heat-balance sap-flow gauge, an electronic lysimeter, and an infrared leaf temperature sensor. One pattern consisted of a steady rate of transpiration in a stable greenhouse environment. The second pattern consisted of large oscillations in transpiration unrelated to any monitored microclimate rhythms. These oscillations had a sine-wave pattern with periods of 50 to 90 minutes and ranged from 2 to 69 g·h-1 in natural light and 3 to 40 g·h-1 under high-pressure sodium lamps at night. Leaf-air temperature difference (T1 - Ta) also oscillated and was inversely related to transpiration rate. Oscillatory transpiration has not been reported in roses. Plant scientists need to recognize the complex and dynamic nature of plant responses such as the oscillatory pattern of WPT monitored in Rosa hybrida when selecting monitoring and control strategies.

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F. Christine Pettipas, Rajasekaran R. Lada, Robert Gordon, and Tess Astatkie

Increasing temperature as a result of global climate change is expected to exert a great influence on agricultural crops, possibly through effects on photosynthesis. Response to temperature of leaf gas exchange parameters of carrot (Daucus carota L. var. sativus) cultivars Cascade, Carson, Oranza, and Red Core Chantenay (RCC) were examined in a controlled growth room experiment. Leaf net photosynthetic rate (PN), stomatal conductance (gs), and transpiration rate (E) were measured at temperatures ranging from 15 to 35 °C at 370 μmol·mol-1 (CO2) and 450±20 μmol·m-2·s-1 PAR. The cultivars responded similarly to increasing temperature and did not differ in most photosynthetic parameters except gs. The PN increased between 20 and 30 °C, thereafter increasing only slightly to 35 °C. On average, increasing temperature from 20 to 30 °C increased PN by 69%. Carboxylation efficiencies (Ca/Ci ratio) ranged from 1.12–2.33 mmol·mol-1 while maximum PN were 3.25, 3.90, 5.49, 4.19 μmol·m-2·s-1 for Carson, RCC, Cascade, and Oranza, respectively. The E did not reach maximum at 35 °C while gs peaked at 30 °C and then decreased by 93% at 35 °C. The water use efficiency (WUE) decreased with an increase in temperature due to increases in both PN and E. The results indicate that increasing temperatures above the seasonal average (<20 °C) increases both PN and E up to 30–35 °C. An increase in photosynthesis due to an increase in temperature is expected to hasten growth. Carrots may be able to withstand a moderate increase in temperature.