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water potential, ( B ) net photosynthetic rate (P n ), ( C ) stomatal conductance ( g S ), and ( D ) intercellular CO 2 concentration (Ci) of leaves of micropropagated apple trees in response to half-root water stress (▼) and whole-root water stress

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.03). These data provide further evidence that the OH tomatoes were water stressed as late-season water deficits are known to increase fruit solids ( Hanson and May, 2005 ; Mitchell et al., 1991 ). Fruit pH did not differ between irrigation treatments with

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Abstract

Polyethylene glycol (PEG-4000)-induced water stress (—0.5 to —7.5 bars) reduced shoot and root growth, water use, and stem 45Ca in seedlings of peach (Prunus persica (L.) Batsch). Sucrose feeding through a leaf did not affect stem 45Ca with or without osmotic stress. 45Calcium uptake per milligram water used was not different at different solution osmotic potentials. A split-root study, with half the root system receiving 45Ca and/or PEG, showed that if 45Ca was supplied only to the water-stressed root half, 45Ca uptake into stems was low regardless of whether the other root half was stressed or not. Results indicate that reduced stem Ca during water stress is probably not a direct result of decreased root energy needed for active uptake or reduced translocation out of the root. Calcium absorption appeared to be related to the amount of unsuberized root surface available for Ca uptake.

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Abstract

Polyethylene glycol (PEG)-induced water stress in nutrient solutions decreased both water consumption and 45Ca uptake by apple seedlings (Malus domestica Borkh.) The decrease in water uptake was more severe than the decrease in 45Ca uptake. When 45Ca uptake was calculated on the basis of water consumption, it was found that 45Ca uptake was not dependent on water uptake although water was necessary for movement of 45Ca. In split-root experiments, PEG and 45Ca were either applied to the same half of the root or to separate halves. Calcium uptake decreased in plants subjected to water stress. The results indicated that the site of this decrease was at the root, not the aerial portion of the plant which, indirectly, may affect root function and thus 45Ca uptake. Split-root experiments also indicated that the unstressed half of the root cannot fully compensate for the stressed half of the root in either water or 45Ca uptake. Water use of plants with half of their root under a −5.0 bar water stress was decreased by 30%. Urea-nitrogen pretreatment did not modify the effect of osmotic stress on leaf Ca, Mg and K concentrations, water use or dry matter production during the period of applied water stress. All these parameters decreased with increasing solution osmotic stress.

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93 ORAL SESSION 25 (Abstr. 186–193) Vegetable Crops: Stress Physiology

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148 POSTER SESSION 5C (Abstr. 281–286) Stress Physiology–Cross-commodity

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Half or whole root systems of micropropagated `Gala' apple (Malus ×domestica Borkh.) plants were subjected to drought stress by regulating the osmotic potential of the nutrient solution using polyethylene glycol (20% w/v) to investigate the effect of root drying on NO3- content and metabolism in roots and leaves and on leaf photosynthesis. No significant difference in predawn leaf water potential was found between half root stress (HRS) and control (CK), while predawn leaf water potential from both was significantly higher than for the whole root stress (WRS) treatment. However, diurnal leaf water potential of HRS was lower than CK and higher than WRS during most of the daytime. Neither HRS nor WRS influenced foliar NO3- concentration, but both significantly reduced NO3- concentration in drought-stressed roots as early as 4 hours after stress treatment started. This reduced NO3- concentration was maintained in HRS and WRS roots to the end of the experiment. However, there were no significant differences in NO3- concerntation between CK roots and unstressed roots of HRS. Similar to the effect on root NO3- concentration, both HRS and WRS reduced nitrate reductase activity in drought-stressed roots. Moreover, leaf net photosynthesis, stomatal conductance and transpiration rate of HRS plants were reduced significantly throughout the experiment when compared with CK plants, but the values were higher than those of WRS plants in the first 7 days of stress treatment though not at later times. Net photosynthesis, stomatal conductance and transpiration rate were correlated to root NO3- concentration. This correlation may simply reflect the fact that water stress affected both NO3- concentration in roots and leaf gas exchange in the same direction.

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’ trees or either treatment on ‘Swingle’ trees. Root-to-shoot dry weight ratio (Rt/St) was also greater for drought-stressed control trees compared with well-watered control trees of both rootstocks ( Fig. 4C–D ). The SWE treatment diminished the increase

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Photinia plants produced in 11.4-liter polyethylene containers using a pine bark-based medium were transplanted into a well-drained sand and irrigated on alternate days. Polyethylene barriers were placed under half the root balls at transplanting to limit gravitational water loss. Plant water potential was measured diurnally between irrigations, and root growth was determined at 4-month intervals. Plants with barriers averaged higher cumulative daily water stress than control plants over the year, although predawn and minimum water potentials were similar. Growth index and trunk diameter were similar for the plants over barriers and controls, but the former were taller after 1 year. Plants with barriers had twice the horizontal root growth into the landscape site as control plants, resulting in twice the root mass in the landscape after 1 year.

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Instrumentation to measure soil respiration is currently readily available. However, the relationship between soil respiration and root activity or root mass is not known. Herein we report on preliminary result using a 13CO2 pulse to the foliage to determine if 13C respiration can be related to either root activity or root mass. An experiment was performed in the field on a 5-year-old apple tree (cv. Jonagold on M7). The tree canopy was enclosed in a Mylar® balloon and 2.1 g 13CO2 were pulsed in the balloon for 1 hr. After the pulse, air emitted by the soil and selected roots was collected every 6 hr for 8 days, by bubbling it in 2 M NaOH. 13C/12C ratios were measured with the mass spectrometer. The emission of 13CO2 from the roots gradually increased after the pulse reaching a peak after 100 hr. The emission trend was not linear, but it seemed related to soil temperature. Leaves and fruit were also collected daily. 13C content in leaves was 1.15% right after the pulse, but it progressively decreased to 1.09% at the end of the experiment. The experiment was then repeated on 12 potted apple trees (cv. Redcort on M7) in greenhouse conditions. Six of them were maintained well-watered, whereas six plants were subjected to a mild water stress, by watering them with half of the volume of water used for well-watered plants. After the two soil moisture levels were achieved, the tree canopies of all the 12 trees were pulsed. Leaves, stems, and roots were ground and run in the mass spectrometer. The results of root emission rate were found to be similar to the field experiment. Results also indicated that, in our experiment, stress did not affect root respiration rate. Specific details of the physiology data will be presented.

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