Search Results
Abstract
The addition of (2RS, 3RS)-1-(4-chlorophenyl)-4,4-dimethyl-2-1,2,4-triazoI-1-yl-) pentan-3-ol) (paclobutrazol, PP333) at 0.05 or 0.20 ppm to a nutrient solution in which 4-month-old apple (Malus domestica, Borkh.) seedlings were growing, reduced terminal growth and increased root to leaf ratio. Plants pretreated with 0.20 ppm PP333 did not show a reduction in transpiration due to subsequent applied water stress induced by polyethylene glycol (PEG), whereas untreated plants decreased their transpiration in response to PEG stress at −0.5 and −0.75 MPa. The PP333 pretreatment at 0.20 ppm improved water balance of the seedlings since they had a higher water potential than untreated seedlings at equal or higher transpiration rates. Leaf osmotic adjustment to lower water potentials was shown to be leaf age-dependent irrespective of PP333 pretreatment.
Abstract
In chlorotic, K-deficient leaves of prune (Prunus domestica L. cv. Agen), leaf water potentials were greater and transpiration less than in green, K-sufficient leaves. These results bring into question the role of leaf desiccation as the primary factor in the browning of K-deficient leaves.
Abstract
Eleven-year-old ‘Golden Delicious’/M. 26 apple (Malus domestica Borkh.) trees were left unthinned (483 fruit/tree), thinned to one fruit/spur (370 fruit/tree), or completely defruited. Leaf water potential, leaf stomatal conductance, and leaf water content were monitored during the growing season. From 3 weeks after thinning and continuing to harvest, trees with an average of 483 or 370 fruit had significantly lower leaf water potentials than defruited trees. Trees thinned to 370 fruit had consistently higher leaf water potentials than unthinned trees with 483 fruit. Leaves on unthinned or one fruit/spur trees had higher stomatal conductances than leaves on completely defruited trees, although these differences were detected later in the season than those for leaf water potentials. No treatment differences in leaf water content were observed. Defruited trees had higher specific leaf weights, longer shoot extension, and greater increases in trunk cross-sectional area than those not defruited. Fruit size was greatest on trees thinned to one fruit/spur.
Abstract
Low- and high-K pretreated ‘York Imperial’ apple seedlings (Malus domestica Borkh.) were grown in nutrient solution cultures. Addition of polyethylene glycol (PEG) to the nutrient solution to reduce water potential to −1.0 bar reduced water consumption, fresh weight, specific leaf weight (SLW), and leaf water potential and increased the amount of water consumed per unit of fresh weight gain. High-K pretreatment increased water consumption of unstressed seedlings but decreased water consumption of PEG-stressed plants. Daily sprays with 0.5% KCl applied in early afternoon had no effect on water consumption rate in apple seedlings. However, sprays probably induced wider stomatal opening, since K-sprayed trees had lower leaf water potential when measured at noon than unsprayed trees. This effect was not observed when water potential was measured in the morning (0800 hr). High-K plants had higher leaf water potential than low-K plants in the morning. Potassium pretreatment and PEG stress as well as K-sprays had numerous effects on plant mineral composition. The K-pretreatment or K-sprays did not alleviate the detrimental effects of PEG-induced water stress despite the effects of K-pretreatment and K-sprays on mineral composition and leaf water potential.
A study was conducted to compare three measurements of determining water status of grapevines (Vitis vinifera L.) in the field. Predawn leaf water potential (ΨPD), midday leaf water potential (Ψl), and midday stem water potential (Ψstem) were measured on `Chardonnay' and `Cabernet Sauvignon' grapevines grown in Napa Valley, California late in the 1999 growing season. Both cultivars had been irrigated weekly at various fractions (0, 0.5, and 1.0 for `Chardonnay' and 0, 0.5, 0.75, and 1.5 for `Cabernet') of estimated vineyard evapotranspiration (ETc) from approximately anthesis up to the dates of measurements. Predawn water potential measurements were taken beginning at 0330 hr and completed before sunrise. Midday Ψl and Ψstem measurements were taken only between 1230 and 1330 hr. In addition, net CO2 assimilation rates (A) and stomatal conductance to water vapor (gs) were also measured at midday. Soil water content (SWC) was measured in the `Chardonnay' vineyard using a neutron probe. Values obtained for ΨPD, Ψl, and Ψstem in this study ranged from about -0.05 to -0.8, -0.7 to -1.8, and -0.5 to -1.6 MPa, respectively. All three measurements of vine water status were highly correlated with one another. Linear regression analysis of Ψl and Ψstem versus ΨPD resulted in r 2 values of 0.88 and 0.85, respectively. A similar analysis of Ψl as a function of Ψstem resulted in an r2 of 0.92. In the `Chardonnay' vineyard, all three methods of estimating vine water status were significantly (P < 0.01) correlated with SWC and applied amounts of water. Lastly, ΨPD, Ψl, and Ψstem were all linearly correlated with measurements of A and gs at midday. Under the conditions of this study, ΨPD, Ψl, and Ψstem represent equally viable methods of assessing the water status of these grapevines. They were all correlated similarly with the amount of water in the soil profile and leaf gas exchange as well as with one another.
Abbreviations: EC, electrical conductivity; MSC, moisture stress conditioning; P L , leaf turgor potential; PV, pressure-volume; RWC, relative leaf water content; SWC, symplastic water content; ψ L , leaf water potential; π 100 , π 0 osmotic
Abstract
The water relations of mycorrhizal onions (Allium cepa L.) were compared with those of non-mycorrhizal controls grown under low and high soil phosphorus conditions. Mycorrhizal plants had higher leaf water potentials, higher transpiration rates, higher hydraulic conductivities and lower leaf resistances than did non-mycorrhizal plants grown in low soil phosphorus conditions. When controls were grown under high soil phosphorus conditions, all 4 parameters were not different from those of mycorrhizal plants. The magnitude of the effect of mycorrhizal fungi on the water relations of the host may, in part, be a function of phosphorus nutrition. The differences in leaf water potentials, transpiration rates and leaf resistances are considered to be the result of the differences found in hydraulic conductivities.
Abstract
Leaf water potentials did not limit stomatal opening of Vitis labruscana Bailey cv. Concord during the summers of 1972 and 1973 in a New York vineyard. Midday leaf-water potentials ranged from −8 to −16 bars and were closely related to individual leaf irradiance. The diurnal variation of leaf, stem, and fruit cluster water potentials on a typical clear day were about 5, 11, and 6 bars, respectively. Water potential gradients at midday across the root, shoot, and petiole-leaf systems averaged about 10, 1 and 3 bars, respectively. The gradient across the root consistently increased throughout the day relative to plant transpiration rate. Minimum stomatal resistance on days after cold nights (less than 10°C) was 2.7 ± 1.1 s cm-1, while the mean resistance on all other days was 1.0 ± 0.5 s cm-1. Cool night temperatures inhibited stomatal opening and closing independently of leaf water potential.
Abstract
Performance of open-top chambers used for air pollutant effect studies on mature grapevines (Vitis labruscana Bailey cv. Concord) was evaluated. The chamber environment was characterized by somewhat higher air temperature and dew point and decreased light intensity and wind velocity compared with ambient conditions. Within the chambers, grapevines had slightly increased leaf temperature. No differences due to chambers were detected on vine stomatal resistance, leaf water potential, or the relationship between leaf temperature and incident radiation.
Five-year old `Hosui' Asian pear (Pyrus serotina Rehder) trees growing in drainage lysimeters and trained onto a Tatura trellis were subjected to three different irrigation regimes. Weekly water use (WU) was calculated using the mass-balance approach. Soil-water content of control lysimeters was kept at pot capacity, while deficit irrigation was applied before [regulated deficit irrigation (RDI)] and during the period of rapid fruit growth [late deficit irrigation (LDI)]. Soil-water content was maintained at ≈50% and 75% of pot capacity for RDI and LDI, respectively. Deficit irrigation reduced mean WU during RDI and LDI by 20%. The reduced WU was caused by lower stomatal conductance (gs) on deficit-irrigated trees. RDI trees had more-negative diurnal leaf water potentials (ψl). The ψl, gs, and WU remained lower for 2 weeks after RDI was discontinued. RDI reduced shoot extension and summer pruning weights, whereas winter pruning weights were not different between treatments. Except for the final week of RDI, fruit growth was not reduced, and fruit from RDI grew faster than the control during the first week after RDI. In contrast, fruit volume measurements showed that fruit growth was clearly inhibited by LDI. Final fruit size and yield, however, were not different between treatments. Return bloom was reduced by RDI but was not affected by LDI.