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Ahmad Shirazi and Arthur C. Cameron

A method was developed to measure transpiration rates and apparent water-vapor permeability coefficients (P'H2O) of detached fruit using an analytical balance equipped with a humidity chamber, wide-range humidity-generating and sensing devices, and a datalogger. The system was designed to monitor weight changes with time and, hence, weight loss of individual fruit during exposure to specific relative humidities (RHs) and temperatures. Weight loss was corrected for loss due to respiratory exchange of 02 and CO2 before calculating P'H2O. Values of P'H2O for tomatoes obtained using this method over periods of 5 minutes to 24 hours ranged from 3 to 12 nmol·cm-2·s-1·kPa-1 at 20C, depending on the experimental conditions. These values are similar to previously published values and to those obtained in a conventional weight-loss experiment, which involved intermittent weighing. P'H20 for tomatoes dropped ≈15% in 24 hours. P'H20 increased with a transient increase in RH; the extent of the increase was variable from fruit to fruit, ranging from 5% to 100% over 30% to 90% RH. The change was reversible in that P'H2O increased and decreased within minutes following shifts in RH. Similar changes were found for strawberry P'H20. The increase in P'H2O may be due, in part, to a direct effect of water vapor on the water transport properties of the cuticular polymer and surface temperature depression as a result of evaporative cooling. At 50% RH and 20C, water vapor diffuses from tomatoes 50 times faster than O2 enters on a molar basis. This information will be useful for modeling RH changes in modified-atmosphere packages.

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Keun Ho Cho, Beyoung Hwa Kwack, Moo Ryong Huh, and Chiwon W. Lee

The biomass yield, transpiration rate, and chlorophyll contents in Cymbidium goeringii plants grown under various light, temperature, and humidity conditions were investigated. Two-year-old plants potted in pine-bark medium were grown for 12 weeks during the summer months in polyethylene film-covered mini-greenhouses having four different environmental conditions: a) closed house (CH) with high humidity (95.1% RH), high light (800 μmol·m–2·s–1) and high temperature (37.5 °C), b) ventilated house (VH) with low humidity (41.4% RH), high light (800 μmol·m–2·s–1), and medium temperature (31.5 °C), c) shaded closed house (SCH) with high humidity (91.0% RH), low light (110 μmol·m–2·s–1) and medium temperature (33.3 °C), and d) shaded ventilated house (SVH) with medium humidity (61.5% RH), low light (110 μmol·m–2·s–1) and low temperature (30.5 °C). Plants grown in CH produced leaf chlorosis with 50% shorter leaves and 40% lower relative growth rate (7.9 mg/g fresh weight per day) compared to plants grown in SVH. Cymbidium plants grown in SCH or SVH showed higher leaf and root dry weights as compared to those grown in CH or VH. Leaf chlorophyll-a and -b contents as well as carbohydrate levels were the highest in plants grown in SVH, indicating the benefits of shading and ventilation. The rate of transpiration showed a quadratic response to increasing levels of leaf temperature (r 2 = 0.81), wind velocity (r 2 = 0.82), and vapor pressure deficit (VPD, r 2 = 0.91). Regression analysis revealed that the maximum transpiration rate occurred at 25.4 °C leaf temperature, 2.1 m/s wind velocity, and 2.3 kPa VPD in this experiment.

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A. Naor and S. Cohen

The sensitivity of water stress indicators to changing moisture availability, and their variability, determine the number of measurements that should be taken in order to represent properly plant water status in a certain orchard. In the present study we examined the sensitivity and variability of maximum daily trunk shrinkage, midday stem water potential, and daily transpiration rate in their responses to withholding irrigation from field-grown drip-irrigated `Golden delicious' apple trees in a commercial orchard. Irrigation was withheld from the stressed trees for 17 days starting in mid-July, and the control trees were irrigated daily at 100% of the “Class A” pan evaporation rate. The courses of daily transpiration rate, maximum trunk shrinkage, and midday stem water potential before and 10 days after the drying period were similar in the control and the stressed trees. Highly significant differences between the stressed and the control trees in their midday stem water potentials were apparent from the early stages of the stress period. Daily transpiration rate and maximum daily shrinkage were more variable than midday stem water potential, and differences between treatments became significant only after measurements were expressed relative to the initial values before irrigation was witheld. Differences between treatments (as percentages of the values obtained for the control trees) increased after irrigation stopped where these differences were greatest for maximum daily shrinkage, which reached 90%; moderate for stem water potential (60%); and least for daily transpiration rate, for which the differences remained below 20%. Our data show that the choice of a certain water stress indicator should be based on both the sensitivity to changing moisture availability and the degree of variability. Possible reasons for the different sensitivity to moisture availability and the different variability between the water stress indicators under study are discussed.

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Toshio Shibuya, Akihito Sugimoto, Yoshiaki Kitaya, Makoto Kiyota, Yuichiro Nagasaka, and Shinya Kawaguchi

the actual g l under growing conditions, because the micrometeorology at the leaf surface is disturbed by covering the leaf with a cuvette. Alternatively, g l also can be estimated by dividing the leaf transpiration rate ( Tr ) by the absolute

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Thanidchaya Puthmee, Kenji Takahashi, Midori Sugawara, Rieko Kawamata, Yoshie Motomura, Takashi Nishizawa, Toshiyuki Aikawa, and Wilawan Kumpoun

-permeable than cuticular membranes ( Lester, 1988 ). However, changes in the transpiration rate of cuticular membranes and net during fruit development have not yet been measured separately. The waterproofing ability of periderm tissue depends not only on its

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Donavon Sonnenberg, Patrick A. Ndakidemi, Ambrose Okem, and Charles Laubscher

wavelength range 400–700 nm) is used in the presence of chlorophyll to synthesis carbohydrate such as sugar from CO 2 and water ( Petela, 2007 ). Photosynthetic rate (A), intercellular CO 2 concentration (C i ), g S , transpiration rate (e), and dry matter

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Yuya Mochizuki, Saori Sekiguchi, Naomi Horiuchi, Thanda Aung, and Isao Ogiwara

under blue and green LEDs ( Fig. 3F ). Fig. 3. Responses of stomatal conductance, leaf intercellular CO 2 concentrations, and transpiration rates to irradiance for the adaxial side of ( A , C , E ) mature strawberry leaves and ( B , D , F ) young

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Toshio Shibuya, Akihito Sugimoto, Yoshiaki Kitaya, and Makoto Kiyota

study, we measured changes in net photosynthetic rate, transpiration rate, and leaf conductance of a seedling community after raising the VPD at various plant densities to evaluate the effects of plant density on gas exchanges under the water stress

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Ji Jhong Chen, Haifeng Xing, Asmita Paudel, Youping Sun, Genhua Niu, and Matthew Chappell

. Fig. 2. Correlations between net photosynthesis rate (P n ), stomatal conductance ( g S ), transpiration rate (E), water use efficiency (WUE), and leaf sodium (Na + ), chloride (Cl – ), the ratio of potassium (K + ) to Na + , and the ratio of calcium

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Ian Merwin and Warren C. Stiles

Eight vegetation management systems (VMS) were evaluated over four years in a newly planted apple site. VMS treatments included pre- and post-emergence herbicide strips, a close-mowed sodgrass, a growth-suppressed (maleic-hydrazide) sodgrass, a crownvetch “living mulch,” clean cultivation, and straw mulch. Soil moisture supply was highest under the straw mulch and lowest under crownvetch, and varied inversely with groundcover biomass. Leaf N was deficient in tress in both sodgrass VMS, and increased by the lequme “living mulch” only after four years. Leaf Cu was lowest, and appeared to limit tree growth in VMS with prolonged soil moisture deficits. No significant differences were observed in leaf transpiration over a broad range (10 to 700 kPa) of soil matric tension. Cumulative trunk crosssectional area was greatest in straw-mulched trees and least in sodgrass and crownvetch VMS. The optimal soil matric tension for nutrient uptake and tree growth appeared to be 175 to 200 kPa in this orchard. Increasing the width of glyphosate herbicide strips from 1.5 to 2.5 m in tree rows did not improve tree growth, nutritional status or fruit yield.