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Open access

S. S. Woltz and W. E. Waters

Abstract

Comparative fumigation procedures were used to evaluate the relative susceptibility of some ornamental plant species to the toxic effects of airborne fluoride in compartmentalized greenhouse chambers. Susceptibility classification was based on the speed of development of toxicity symptoms together with the specific concentrations of hydrofluoric acid vapor causing fluorosis. Symptoms of fluoride toxic effects were recorded for use in diagnosis and evaluation of damage.

Open access

W. O. Harrington, Claude H. Hills, Susan B. Jones, A. E. Stafford, and B. R. Tennes

Abstract

Spraying with 3% ethyl oleate (EO) reduced the incidence of cracking from 29 to 11% in ‘Vista’ cherries (Prunis avium L.) Applications of EO increased the rate of dehydration in cherries exposed to ambient air following treatment. Scanning electron microscopy (SEM) observations suggest that EO modifies the cherry cuticle by redistributing surface wax, thereby enhancing mass transfer of water vapor through the skin.

Free access

D. Michael Glenn

productivity, contrary to the assertion of Blum (2005) . Environmental effects on WUE include the response to the abiotic environmental effects of vapor pressure deficits (VPD), photosynthetically active radiation ( PAR ), and water deficits in addition to

Free access

Roberto G. Lopez and Erik S. Runkle

were provided when the integrated light intensity reached 0.20 mol·m −2 ·h −1 or after 60 min, whichever occurred first. A vapor-pressure deficit of 0.3 kPa was maintained by the injection of steam or fine mist (Humidifan Turbo XE; Jaybird

Free access

Phil S. Allen, Donald B. White, Karl Russer, and Dave Olson

An inexpensive system for maintaining desired water potentials throughout seed germination was developed. During hydration, a water reservoir at the base of inclined petri dishes allowed continual saturation of filter paper on which seeds were placed. During dehydration, seeds were exposed to equilibrium vapor pressures above saturated salt solutions. Constant temperature, necessary to prevent condensation of water vapor, was achieved via a small (0.2 A) fan that furnished and circulated heat throughout an insulated chamber in which salt solutions were placed. By operating the chamber above ambient laboratory temperature, interior cooling was not required. The system allowed manipulation of the rate, degree, and frequency of dehydration episodes to which germinating seeds were exposed.

Free access

Derek P. Whitelock, Gerald H. Brusewitz, Michael W. Smith, and Xihai Zhang

This study examined the effects of high humidity (>95%) and airflow on fresh peach [Prunus persica (L.) Batsch.] quality. Peaches were stored in high airflow at 98%, 88%, and 67% relative humidity (RH) (6, 5.6, and 4.3C, respectively) and negligible airflow at 100%, 95%, and 81% RH (6, 5.6, and 4.3C, respectively). Fruit weight loss, penetrometer force, impact variables, and bruise occurrence from a single 15-cm drop impact were measured over 20 days of storage. Fruit stored at a low vapor pressure deficit had a lower rate of weight loss, with drop impact values characteristic of firmer fruit than fruit stored at higher vapor pressure deficits. High airflow increased weight loss and decreased fruit firmness, but had only a secondary effect on localized humidity. Penetrometer force and bruise occurrence were less sensitive than drop impact variables in detecting differences in fruit firmness due to treatments.

Free access

Steven E. Woerner and Douglas A. Hopper

A computer simulation model was developed to be used in evaluating irrigation scheduling techniques and assisting irrigation scheduling decisions under greenhouse conditions in Colorado. The model simulates variable greenhouse conditions and shows how each of four irrigation scheduling techniques responds to these conditions. Reports from the model detail numbers of irrigation events, sensitivities to parameters, and forecasts water usage. The model was also used to determine appropriate accumulation triggers for Colorado conditions.

Four techniques evaluated here include: time clock control; accumulated radiation; accumulated vapor pressure deficit; combination method (radiation and vapor pressure deficit). The model has shown the combination method to be the most sensitive to changes in environmental conditions, while the time clock method proved to be least sensitive (and most wasteful of water).

The model may evaluate additional irrigation scheduling techniques by including additional parameters in the model, and may readily be adapted to different climatic regions.

Free access

Chien Yi Wang and J. George Buta

Freshly harvested unwaxed `Marsh Ruby' grapefruit (Citrus paradisi Macfad.) were obtained from Wabasso, Fla. The fruit were treated with methyl jasmonate by dipping, pressure infiltration (82.7 kPa for 3 minutes), or vapor fumigation. Control fruit were similarly treated with distilled water. All fruit were then stored at 1°C. Samples from all treatments were transferred to 20°C for 3 days after 4 and 10 weeks of storage at 1°C for evaluation of chilling injury. Symptoms of chilling injury were negligible in all treatments after 4 weeks of storage. However, after 10 weeks of storage, moderate to severe pitting occurred in the control fruit but the severity of chilling injury was significantly reduced by methyl jasmonate treatments. The most effective treatments were either pressure infiltration using a 0.1 mm emulsion or fumigation with vapor at saturation.

Open access

Jose M. Montano and William M. Proebsting

Abstract

Various storage treatments were imposed on cut douglas-fir Christmas trees to measure drying relative to the damage threshold ψ of −3.5 MPa. In a greenhouse (day/night 16°/10° ± 5°C, RH 70-95%), cut douglas-fir dried to −3.5 MPa in 4 days. Overhead irrigation under these conditions maintained ψ about − 3.2 MPa for 9 days. Outdoors (day/night 672° ±9°), ψ declined to a range of −2.5 to −3.0 MPa depending on the weather. Overhead irrigation outdoors maintained ψ between −1.0 to −2.5 MPa. The antitranspirants tested did not reduce the rate of water loss significantly in the greenhouse. Outdoors, ψ of Vapor Gard-treated trees was similar to the irrigated trees, but Vapor Gard caused serious cosmetic defects. None of the other antitranspirants tested reduced moisture loss outdoors.

Open access

P. Lorenzo-Minguez, R. Ceulemans, R. Gabriels, I. Impens, and O. Verdonck

Abstract

The effects of air temperature and leaf-to-air vapor pressure deficit (VPD) on the gas exchange behavior, i.e., net CO2 exchange rate (NCER) and dark respiration rate, transpiration, leaf diffusive conductance to water vapor, water use efficiency (WUE), and xylem pressure potential of Schefflera arboricola Hayata ‘Compacta’ were examined under conditions of adequate substrate moisture in a controlled environment growth chamber. The optimum temperature for NCER was around 25°C at a photo-synthetic photon flux density (PPFD) of 450 μmol s-1m-2 and an ambient CO2-concentration of about 350 cm3.m-3. With increasing VPD, transpiration increased while leaf diffusive conductance as well as leaf temperature decreased. Due to humidity induced stomatal closure, WUE expressed per unit of VPD also decreased. Changes in VPD did not significantly affect NCER and xylem water potential.