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J.H. Crane and B. Schaffer

The effect of wind stress on growth, net CO2 assimilation (A), and leaf water potential of eighteen-month-old, containerized carambola (Averrhoa carambola cv. Arkin) and seedling sugar apple (Annona squamosa) trees was investigated. In a glasshouse, trees were exposed to fan-generated wind speeds of 0 (control), 4 (low wind; LW), or 7 (high wind; HW) m sec-1 for 4 hr/day (1000-1400 hr) for 30 days. No differences in A, stomatal conductance, transpiration, and fresh and dry wt of mature carambola or sugar apple leaves or shoots were observed among treatments. In contrast, as wind speed increased, fresh wt of immature carambola leaves and shoots decreased. For carambola and sugar apple, no significant relationship was found between mid-day leaf water potentials and wind speed. However, after 30 days, leaf water potential of carambola subjected to HW (-1.2 MPa) was lower than those of LW (-1.1 MPa) and control (-1.1 MPa) trees. For sugar apple, leaf water potential of control trees was generally higher than those of trees in the LW and HW treatments. The data indicate that exposure to wind speeds of 4 or 7 m sec-1 for as little as 4 hr/day for 30 days reduces new leaf and shoot growth of carambola trees.

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Julián Miralles, Raquel Valdes, Juan J. Martínez-Sánchez, and Sebastián Bañón

calculated with the image analysis software for plant disease quantification ASSESS 2.0 (University of Manitoba, Winnipeg, Canada). Leaf potentials. Midday leaf water potential (Ψ hmd ), midday leaf ψ S (Ψ omd ), and midday leaf turgor potential (Ψ pmd

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Thammasak Thongket and James O. Garner Jr.

Responses of four sweetpotato genotypes (`Centennial', `Travis', `Vardaman' and `MS 21-2') to water stress were studied. Two irrigation regimes (irrigation vs non-irrigation) were imposed on five-week old cuttings grown in a greenhouse environment. Transpiration and leaf diffusive resistance (LDR) were measured with a steady state porometer and mid-day total leaf water potentials were determined with a thermocouple psychrometer. Leaf growth was inhibited earlier than root growth. Water stress caused a reduction of leaf size in Centennial and in leaf number in the other three. Storage root number of Vardaman was not inhibited by limited soil moisture but development of storage roots was retarded by water stress. Total growth under non-irrigation of MS 21-2 was inhibited more than Vardaman. Mid-day leaf water potential did not show promise as a good indicator of water status. Genotypic differences in the water stress sensitivity as measured by LDR, were observed.

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Cynthia B. McKenney and Marihelen Kamp-Glass

The effectiveness of antitranspirant type and concentration on the leaf water relations of Saliva splendens F. `Firebird and Petunia × hybrida Juss. `Comanche'. Two film-forming antitranspirants, Cloud Cover and Folicote, were tested at three different concentrations in two different environments. The leaf water potential, stomatal conductance, and relative water content were evaluated. Transpiration per unit vapor pressure deficit and stomatal conductance for both crops decrease slightly but there was no trend with respect to the film type, environment or concentration rate. The leaf water potentials and relative water content did not show significant difference after antitranspirant application. In order for antitranspirant application to be of benefit to the growth of herbaceous plants, a more durable coating that remains semipermeable would have to be utilized.

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Kirk D. Larson, Bruce Schaffer, and Frederick S. Davies

The effect of flooding on container-grown `Tommy Atkins' mango (Mangifera indica L.) trees on two rootstock, and on container-grown seedling `Peach' mango trees, was investigated by evaluating vegetative growth, net gas exchange, and leaf water potential. In general, flooding simultaneously reduced net CO2 assimilation (A) and stomatal conductance (gs) after 2 to 3 days. However, flooding did not affect leaf water potential, shoot extension growth, or shoot dry weight, but stem radial growth and root dry weight were reduced, resulting in larger shoot: root ratios for flooded trees. Mortality of flooded trees ranged from 0% to 45% and was not related to-rootstock scion combination. Hypertrophied lenticels were observed on trees that survived flooding but not on trees that died. The reductions in gas exchange, vegetative growth, and the variable tree mortality indicate that mango is not highly flood-tolerant but appears to possess certain adaptations to flooded soil conditions.

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Roger Kjelgren and Bradley H. Taylor

The response of foliage-air temperature differential (Tl-Ta) to vapor-pressure deficit (VPD) as a means of detecting incipient water stress was investigated in the Illinois planting of the NC-140 Uniform Peach Rootstock Trial. Stomatal conductance, foliage temperature, leaf water potential, air temperature and VPD were followed diurnally on three dates in 1989 for mature `Redhaven' on six different rootstock. On two of three sampling dates where predawn leaf water potential was greater than -0.5 MPa there was no indication of midday stomatal closure and all rootstock exhibited an inverse relationship between T1-Ta and VPD. On the date with the most negative predawn leaf water potential, T1-Ta of two plum rootstock (GF-677 and GF-655-2) was observed to be significantly greater at VPD levels above 2 kPa than the remaining rootstock. All rootstock on this date exhibited greater T1-Ta than at similar VPD levels on the other two dates. These data suggest that transpirational cooling plays a large enough role in foliage temperature regulation of `Redhaven' peach such that incipient water stress and rootstock effects on water relations can be detected through increases in foliage temperature.

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Thayne Montague, Roger Kjelgren, and Larry Rupp

Gas exchange and growth of transplanted and nontransplanted, field-grown Norway maple (Acer platanoides L. `Schwedleri') and littleleaf linden (Tilia cordata Mill. `Greenspire') trees were investigated in an arid climate. In the spring of 1995, three trees of each species were moved with a tree spade to a new location within a field nursery and three nontransplanted trees were selected as controls. Predawn leaf water potential, morning-to-evening stomatal conductance and leaf temperature, leaf-to-air vapor pressure difference, midday stomatal conductance and photosynthetic rate, and growth data were collected over a 2-year period. After transplanting, weekly predawn leaf water potential indicated that transplanted trees were under greater water stress than were nontransplanted (control) trees. However, predawn leaf water potential of maple trees recovered to control levels 18 weeks after transplanting, while that of transplanted linden trees remained more negative than that of controls. In 1995, stomatal conductance and photosynthetic rates were lower throughout the day for transplanted trees. In 1996, gas exchange rates of transplanted maple trees recovered to near control levels while rates for transplanted linden trees did not. Sensitivity of stomata to leaf-to-air vapor pressure difference varied with species and with transplant treatment. Each year transplanted trees of both species had less apical growth than did control trees. Although gas exchange and apical growth of transplanted trees was reduced following transplanting, recovery of gas exchange to control rates differed with species.

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J. Roger Harris and Edward F. Gilman

Abbreviations: CER, carbon exchange rate; FC, fabric containers; FG, field grown; PC, plastic containers; Ψ leaf , leaf water potential. 1 Current address: Urban Horticulture Institute, 20 Plant Science Bldg., Cornell Univ., Ithaca, NY 14853

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David W. Wolfe, Daniel T. Topoleski, Norman A. Gundersheim, and Betsy A. Ingall

1 To whom reprint requests should be addressed. This work was supported by U.S. Dept. of Agr. Hatch Grant NYC 161422 (DWW). We thank S. McKay for assistance in preparation of the field plots and J. Melkonian for assistance with leaf water potential

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Toshio Shibuya, Ryoko Terakura, Yoshiaki Kitaya, and Makoto Kiyota

Application of a low-relative-humidity treatment (LHT) to seedlings can reduce water stress on cuttings harvested from the seedlings, after the cuttings are planted. Effects of illumination during LHT and LHT duration on leaf water potential and leaf conductance in cucumber (Cucumis sativus L.) seedlings used as the model plant material and on growth of harvested cuttings were investigated to determine optimal LHT conditions. The seedlings received LHT for 12 or 24 h in a lighted or dark growth chamber at air temperatures of 28 to 31 °C and relative humidity of 12% to 25%. Cuttings including a foliage leaf and two cotyledons were harvested by cutting the hypocotyl of the seedlings immediately after the treatment, and then the cuttings were planted in vermiculite medium. Four days after planting, the total fresh weight of the cuttings from seedlings that had received LHT in the lighted chamber was 2.2 times that of cuttings from seedlings that had not received LHT, whereas the total fresh weight of those that had received LHT in the dark increased by 1.3 to 1.8 times. Significant effects of illumination during LHT were also observed in the transpiration rate and growth of the cuttings, harvested following the treatment, after they were planted. By varying LHT duration, it was also found that leaf water potential and leaf conductance of the seedlings decreased as LHT duration increased up to 18 h. Thus, illumination during LHT increased the growth of cuttings taken following the treatment, and optimal treatment duration of around 18 h was estimated from the seedlings' leaf conductance and leaf water potential.