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Steve C. Yuza, Art L. Youngman, and John C. Pair

This study examined physical factors and physiological responses of five different ecotypes and cultivars of Acer saccharum and A. nigrum. The objective was to determine variations in leaf conductance and xylem water potential and correlations associated with their natural geographic distribution. Compared were two ecotypes of sugar maple, Caddo and Wichita Mountains, native to Oklahoma with cultivars Green Mountain and Legacy, plus black maple seedlings from Iowa. Measurements taken included leaf conductance, xylem water potential and soil water potential in a replicated block of 15-year-old trees. The two ecotypes had consistently higher photosynthetic rates, stomatal conductance and transpiration rates than other selections. Xylem water potentials were significantly higher for Caddo maples than Green Mountain, Legacy and Acer nigrum in both predawn and midday samples. This difference in water availability can be associated with a tendency for Caddo to vary its stomatal conductance. The other tree types maintained stable stomatal conductances.

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Baolin Zhang and Douglas D. Archbold

Plants of F. chiloensis cv. BSP14 (FC) and F. virginiana cv. NCC85-13V (FV) were stressed until wilting, then watered for 2 days prior to measurement. Diurnal measurements of leaf conductance and water relations were conducted. Leaf conductance of stressed FC plants was generally lower, than that of controls at most times, but there wee no difference between the two in FV. Leaf conductance and transpiration rates had not fully recovered to pre-stress levels within this recovery period, Leaf wafer potential declined from predawn to midday, more in stressed than control plants of both species. Leaf osmotic potential averaged 0.4 and 0.2 MPa lower in stressed than control FC and FV plants, respectively, Greater differences occurred at midday than predawn. Leaf pressure potential of stressed plants was higher predawn than midday, 1.4 vs. 0.7 MPa, in FC; it was not different for FV at most times. The difference in water relations between these two species may be explained by a greater residual effect from the osmotic adjustment in FC es compared to FV that occurred during prior water deficit stress.

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D. Joseph Eakes, Robert D. Wright, and John R. Seiler

Abbreviations: CA, leaf chamber CO 2 concentration; CI, leaf internal CO 2 concentration; E, transpiration; g L , leaf conductance; MSC, moisture stress conditioning; Pn, net photosynthesis; r m , mesophyll resistance to CO 2 ; SI, stomatal

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Maria Gomez-del-Campo

orchard of ‘Cornicabra’ was subjected to four irrigation regimes during the second and third years after planting to determine if water stress could be useful for enhancing early olive fruit production. Stem water potential and leaf conductance were

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Leon H. Allen Jr., Mary P. Brakke, and James W. Jones

A water flow model was developed which uses irradiance, leaf-to-air vapor concentration difference, and soil water potential to establish stomatal conductance. Water flow to the roots was computed using a linear approximation of radial flow through the soil toward the axis of the roots across concentric shells. Root length density and soil rooting volume within four separate layers or compartments were included in the model. The simulation was executed in small time step iterations. A small increment of transpiration was translated to a water content deficit at the root and then sequentially through the concentric shells to simulate water uptake and change of soil water potential. The change in soil water potential was used to increment changes in stomatal conductance and transpiration. The output of the model simulated the pattern of diurnal stomatal behavior observed in other types of experiments, as well as the total soil water extraction patterns of young potted citrus trees.

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

velocity in the canopy ( Kim et al., 1996a , 1996b ; Kitaya et al., 1998 ). On the other hand, increasing plant density may enhance CO 2 exchange of the leaf when the CO 2 supply to plants is limited by a decrease in leaf conductance resulting from

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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.

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Chris A. Martin, Sean A. Whitcomb, and Jean C. Stutz

and unpruned shrubs was similar. However, during June, leaf g s of unpruned shrubs was ≈57% less than sheared shrubs. Table 2. Effect of frequent shearing on net carbon assimilation (A) and leaf conductance ( g s ) of Leucophyllum frutescens

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Susan L. Steinberg, Jayne M. Zajicek, and Marshall J. McFarland

Growth of potted Ligustrum was controlled by uniconazole at 3.0 mg a.i./pot. Uniconazole inhibited growth by inducing shorter internodes with smaller diameter and by reducing secondary branching and new leaf production. As a result, the total leaf area of the treated plants was 6396 less than the control plants. The chlorophyll content of recently expanded leaves was 27% lower in treated than in control plants, even though there were no visual differences in leaf color. Leaves of treated plants also had a 28% higher stomatal density than the control. The liquid flow conductance of Ligustrum was 3.7 × 10-14 m·s-1·Pa-1 and was similar for plants in both treatments. Differences in daily water, use between the two treatments began to appear at the same time as differences in growth. Total water use of treated plants was 13% less than that of the control. When daily water use was normalized on a-leaf-area basis, water use between treatments was similar, suggesting that differences in total water use were primarily due to differences in leaf area. For plants in both treatments, peak sap flow rates in the main trunk ranged between 60 and 100 g·h-1·m-2. Leaf conductance, transpiration rates, and water potential were also similar for treated and control plants. Chemical name used: (E)-1-(4-chlorophenyll) -4,4, -dimethyl-2-(l,2,4-triazo1-l-y1)-l-penten-3-ol (uniconazole).

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Mark Rieger

Growth, gas exchange, root hydraulic conductivity, and drought response of seedling and rooted cuttings of Lovell and Nemaguard peach [Prunus persica (L.) Batsch], and Carrizo (Poncirus trifoliata × Citrus sinensis) and sour orange (C. aurantium L.) citrus rootstocks were compared to determine the influence of propagation method on these characteristics. Rooted peach cuttings had a higher proportion of root biomass in fibrous roots (≤ mm in diameter) and lower root: shoot ratios than seedlings, although this did not occur in citrus. Net CO2 assimilation (A) was higher for peach seedlings than for cuttings, but similar for `Redhaven' (RH) scions on either seedling- or cutting-propagated rootstocks, suggesting that leaf-associated factors were responsible for differences. As in peach, A was higher for Carrizo seedlings than for cuttings, but A was not affected by propagation method in sour orange. Peach seedlings maintained higher A than cuttings as water potentials declined during short-term soil drying, although in citrus this occurred only for Carrizo. RH scions on either root type exhibited similar declines in A as soil dried, indicating the lack of a rootstock effect. Root hydraulic conductivity (Lp) was similar between seedlings and cuttings of all cultivars when expressed on a length basis. Leaf conductance and osmotic adjustment were similar for RH scions on seedling- or cutting-propogated rootstocks during 45 days of drought stress, indicating the lack of a rootstock effect on long-term stress response.