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Wanploy Jinagool, Lia Lamacque, Marine Delmas, Sylvain Delzon, Hervé Cochard, and Stéphane Herbette

liquid sap metastable, with a risk of vaporization by cavitation inside conduits, which increase considerably in plants during drought. Cavitation causes a conduit to become air-filled or embolized and unable to transport water ( Tyree and Sperry, 1989

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Michael D. Remmick and Leslie H. Fuchigami

Stems of 1-year seedling Washington hawthorn (Crataegus phaenopyrum) and 1-year layers of apple rootstocks M.9 and M.26 EMLA were subjected to positive air pressures in a double-open-end pressure chamber to determine the cavitation response of each taxon. Inferences regarding relative desiccation tolerance of the taxa can be made by comparing the range of applied pressures over which air-seeding and subsequent reduction of water flux through xylem conduits is induced. M.9 rootstock maintained higher levels of water flux relative to M.26 EMLA or Washington hawthorn at pressures between 3.0 to 4.0 MPa, suggesting greater resistance to water stress-induced air-seeding in the former compared to the latter two taxa. The cavitation responses of M.26 EMLA and Washington hawthorn were indistinguishable from each other. Inferences regarding water stress-induced cavitation response will be discussed relative to this technique.

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Patricia R. Knight, J. Roger Harris, and Jody K. Fanelli

Root severance during field harvesting alters the water status of a tree, resulting in water stress and reduced post-transplant growth. Two experiments, using Acer rubrum L. (red maple), determined the influence of root severance at harvest on sap flow and xylem embolism. Trees 1.5–1.8 m tall (4 years old) were utilized in the first experiment, and trees 1.2–1.5 m tall (2 years old) were utilized in the second. Sap flow sensors were installed on the 4-year-old trees prior to root severance and remained on the trees until 1 week after harvest. Within 1 day after root severance sap flow was reduced and remained lower than nontransplanted (control) trees for the remainder of the experiment. Leaf stomatal conductance (Cs) of transplanted trees 1 week after root severance was lower than that of control trees, but leaf water potentials (ψ) were similar. In the second experiment, sap flow was reduced relative to control trees within 2 h after root severance. Although Cs was reduced 4 hours after root severance, ψ was not. Embolism increased within 24 hours of root severance. These results indicate that root severance quickly induces increased levels of embolism, which is associated with reduced sap flow.

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Gerard W. Wall and Guy McDonnell

Net primary productivity of a botanical is often determined by monitoring gas exchange rates (i.e., CO2, H2O) in a controlled-environment cuvette. Because atmospheric conditions (i.e., incident photon flux density, air temperature, and water vapor pressure) change within a day, whereas edaphic (i.e., soil-water content and nutrient availability) conditions change across days, experimental results obtained between treatment variants can often be confounded within the sample interval. Consequently, in order to obtain a “snapshot” of the CO2 and H2O flux of a botanical across treatment variants, all in situ measurements must be made within a discrete interval. One approach would be to use multiple cuvettes to measure CO2 and H2O flux across all treatment variants simultaneously. But, this would be expensive in both equipment and personnel cost. A more economical approach would be to rapidly excise a botanical from each treatment variant within a discrete interval and store them under exacting steady-state laboratory conditions for in vivo rather than in situ studies. However, this too can be problematic, because in order to excise a botanical a standard operating procedure (SOP) is required. Hence, a need exists for a Rapid Excision Apparatus for Plants (REAPer). Following the SOP of the REAPer enables personnel to excise a botanical across all treatment variants within a discrete interval, while maintaining xylem conductance, minimizing mechanical damage, and providing a uniform sample for in vivo rather then in situ studies. This work describes the design, implementation, and functionality of the REAPer, its application in basic research and development, and its potential applications in the commercial floral and horticultural industries.

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Krista C. Shellie

`Manila' mangoes (Mangifera indica) were immersed in 46C water for 65 or 75 minutes, or exposed to 45, 50 or 52C moist, forced-air (MFA) for 240, 100, and 98 minutes, respectively Mangoes exposed to 50 or 52C MFA had a significantly higher incidence of internal cavitation than mangoes exposed to 45C MFA; mangoes immersed in 46C water for 65 or 75 minutes, or control fruit. Shrink wrapped and nonshrink wrapped mangoes were exposed to 45C MFA for 240 minutes or 52C MFA for 98 minutes to evaluate whether the concentration of oxygen and carbon dioxide inside the fruit influenced cavitation development. Shrink wrapping per se had no significant effect on cavitation development Mangoes heated in 45C MFA for 240 minutes, 52C MFA for 98 minutes, or 46C water for 65 minutes were hydrocooled in 23C water or air cooled at 23C to evaluate whether heat dose influenced cavitation development. Hydrocooling had no significant effect per se on cavitation development though it significantly reduced the heat dose. The above results suggest that tolerance of 'Manila' mango to disinfestation heat treatments is more influenced by a maximum flesh temperature threshold than the heating method, heat dose, or fruit internal atmosphere.

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Şemsettin Kulaç, Pascal Nzokou, Deniz Guney, Bert Michael Cregg, and Ibrahim Turna

be done against xylem cavitation when a reduced soil water supply is coupled with an increase evaporative demand under droughty conditions. Conclusions This study investigated the effect of drought stress on growth, photosynthetic pigments, and

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William W. Inman and William L. Bauerle

Recent work has shown that stomatal conductance (gs) and net photosynthesis (Anet) are responsive to the hydraulic conductance of the soil to leaf pathway (Xp). Two tree species with differing xylem structures were used to study the effect of systematic manipulations in Xp that elevated xylem hydraulic resistance. Simultaneous measures of gs, Anet, bulk leaf abscisic acid concentration (ABAL), leaf water potential (L), and whole plant transpiration (Ew) were taken under controlled environment conditions. Quercus shumardii Buckl. (shumard oak), a ring porous species and Acer rubrum L. `Summer Red' (red maple), a diffuse porous species, were studied to investigate the short-term hydraulic and chemical messenger response to drought. Both species decreased Anet, gs, L, and Ew in response to an immediate substrate moisture alteration. Relative to initial well-watered values, red maple Anet, gs, and Ew declined more than shumard oak. However, gs and Anet vs. whole-plant leaf specific hydraulic resistance was greater in shumard oak. In addition, the larger hydraulic resistance in shumard oak was attributed to higher shoot, as opposed to root, system resistance. The results indicate hydraulic resistance differences that may be attributed to the disparate xylem anatomy between the two species. This study also provides evidence to support the short-term hydraulic signal negative feedback link hypothesis between gs and the cavitation threshold, as opposed to chemical signaling via rapid accumulation from root-synthesized ABA.

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Jingjing Yin, Nina L. Bassuk, Madeline W. Olberg, and Taryn L. Bauerle

water to avoid cavitation. The remaining root stump was connected to HCFM and K of the entire root system was measured as described previously as fine roots. All leaves were removed from stems and scanned using a leaf area meter (LI-3100; LI

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Aidan D. Farrell, Sarah Evelyn, Adrian M. Lennon, and Pathmanathan Umaharan

in hydraulic conductance and RWC of the stem apparently resulting from cavitation. Our conclusion does not support the previous suggestion that water stress in the anthurium spathe is the result of occlusion at the base of the peduncle ( Elibox and

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David R. Bryla and Bernadine C. Strik

the threshold of cavitation in ‘Bluecrop’, protecting it from total xylem cavitation and enhancing its ability to recover from drought. Plant water potentials in the present study were certainly well within the range to induce stomatal closure at