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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.

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.

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

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.

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.

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.

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 (g_s) 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.

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.