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Abstract
Two groups of 8-year-old ‘Murcott’ [Citrus reticulata Blanco × C. sinensis (L.) Osbeck hybrid?] trees on rough lemon (C. jambhiri Lush.) rootstock were transplanted with a Vermeer tree digger in March and July, respectively. Root and shoot pruning and a 2% (v/v) spray of a pinolene-based antitranspirant (Vapor Gard) formed the treatments either individually or in combination. Canopy size at transplanting had the greatest effect on tree water-stress and subsequent tree growth and yield. The antitranspirant and root pruning tended to reduce leaf water-stress, but the effects generally were small and nonsignificant. Root pruning also seemed to stimulate new root growth. After transplanting, roots grew 2 to 3 m beyond the soil ball in one year. Four years after transplanting there were virtually no differences in tree height or canopy volume. Cumulative yield was less for trees with 30% and 85% of their foliage removed as compared to those with 50% removed. Trees pruned 50% bore fruit the year after transplanting and consistently yielded more throughout the study.
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 (gs) 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.
1 To whom reprint requests should be addressed. This work was supported by U.S. Dept. of Agr. Hatch Grant NYC 161422 (DWW). We thank S. McKay for assistance in preparation of the field plots and J. Melkonian for assistance with leaf water potential
Abbreviations: CER, carbon exchange rate; FC, fabric containers; FG, field grown; PC, plastic containers; Ψ leaf , leaf water potential. 1 Current address: Urban Horticulture Institute, 20 Plant Science Bldg., Cornell Univ., Ithaca, NY 14853
Abstract
Water relations responses of 21-year-old grapefruit trees (Citrus paradisi Macf.) irrigated by three types of irrigation systems were compared. Drip, undertree microsprinkler, and overhead sprinkler with application levels of 150 and 450 mm of water per year were compared. Leaf water potential, stomatal conductance, and soil water status were measured under field conditions on a deep, well-drained sandy soil in central Florida. In the early part of a dry spring period, there were no differences in midday or early morning leaf water potential, but, by the end of this period, significant differences in leaf water potential were found among all three irrigation treatments. Highest leaf water potential and stomatal conductance values were maintained in the overhead sprinkler blocks. No midday stomatal closure was observed under the conditions of this study. Relationships among diurnal leaf water potentials, vapor pressure deficits, and stomatal conductance showed hysteresis; this affected the correlations among these factors. Greater water stress occurred in trees irrigated with drip than in trees irrigated with overhead sprinkler systems, but responses to microsprinklers were generally intermediate between the overhead sprinkler and the drip treatments. In an area with high rainfall and sandy soils, increased irrigation coverage can reduce leaf water stress.
Abstract
Leaf water relations and soil-to-leaf resistance were studied in 3-month-old pecan [Carya illinoenis (Wangenh.) C. Koch] seedlings as soil dried progressively to minimum water potentials of −0.3, −0.6, and −1.1 MPa in three separate tests. Leaf conductance, transpiration, and predawn leaf water potential declined with increasing soil water deficits, and only predawn leaf water potential fully returned to pre-stress levels after rewatering. Reduced levels of leaf conductance following water stress were apparently caused by internal factors other than leaf water potential. Leaf conductance of well-watered seedlings decreased logarithmically and with increasing leaf-to-air vapor pressure gradient. Soil-to-leaf resistance to water flow varied diurnally and generally increased following water stress at minimum soil water potentials of −0.6 and −1.1 MPa. Osmotic adjustment and changes in the distribution of water between the apoplast and symplast in leaves did not occur in response to soil water potentials of −0.6 MPa.
Abstract
Leaf water potential of ‘Valencia’ orange trees was influenced by soil water availability, soil temp, and vapor pressure deficit (VPD) of the atmosphere. Low soil water availability prevented full nighttime recovery from water stress. Soil temp below 15°C decreased root permeability for water absorption and contributed to low daytime water potentials (high water stress), but at night when transpiration was minimal, complete recovery occurred. VPD effects on leaf water potential were also most noticeable during the day. Stage II fruits exhibited a recurring diurnal size change during daylight hr. This reversible shrinkage was correlated with simultaneous changes in fruit and leaf water potential and fruit diffusion resistance. However, the irreversible nighttime growth rate could not be correlated with day or night water potentials or air temp, or with night VPD. While differences between fruit and leaf water potentials occurred, no evidence presented here or elsewhere permits an unequivocal statement that transpiring fruits can behave as a midday reservoir of water for leaves.
Abbreviations: CSTR, continuously stirred tank reactor; PLA, planar leaf area; π osmotic potential; ψ leaf , leaf water potential. 1 Current address: 620 Shadywood Lane, Raleigh, NC 27603. This paper is a portion of a thesis submitted by J.M.P. in
Abstract
Water potential, diffusive resistance, and abscisic acid (ABA) were measured at 10-12 day intervals from May to October in leaves from irrigated and non-irrigated peach (Prunus persica L. cv. Fay Elberta) trees, and measurements were taken at intervals from sunrise to sunset on September 8. Leaf water potential, before sunrise, was between −5 and −8 bars in irrigated trees during the entire season whether drip irrigated at 100% evapotranspiration (ET) or 50% ET. Non-irrigated trees showed a decrease in pre-dawn leaf water potential with time, following a pattern similar to that of decreasing soil moisture. Leaf water potential values taken during the afternoon were not associated with soil moisture and did not reflect the stressed condition of the trees. In non-irrigated trees stomatal resistance at mid-day increased rapidly after mid-summer as leaf water potential decreased. ABA concentration in leaves from irrigated trees ranged from 30 to 80 ng/g fresh wt during the entire season. In non-irrigated trees the ABA concentration increased sharply after mid-summer; this was associated with an increase in leaf diffusive resistance and a decrease in leaf water potential. Diurnal variations in leaf water potential were associated with changes in soil moisture, air temperature, relative humidity, and stomatal resistance. Leaf diffusive resistances were similar for all treatments until 1100 hr after which a notable increase occurred with increasing stress, ultimately leading to stomatal closure. ABA concentrations in leaves from irrigated and non-irrigated trees increased as leaf diffusive resistance increased; however in stressed trees, high levels of ABA in the morning were not associated with closed stomata.
Interrelations between water potential and fruit size, crop load, and stomatal conductance were studied in drip-irrigated `Spadona' pear (Pyrus communis L) grafted on quince C (Cydonia oblonga L.) rootstock and growing in a semi-arid zone. Five irrigation rates were applied in the main fruit growth phase: rates of 0.25, 0.40, 0.60, 0.80, and 1.00 of “Class A” pan evaporation rate. The crop in each irrigation treatment was adjusted to four levels (200 to 1200 fruit per tree) by hand thinning at the beginning of June 1999. The crop was harvested on 1 Aug. 1999, and fruit size was determined by means of a commercial sorting machine. Soil, stem, and leaf water potentials and stomatal conductance were measured during the season. Crop yield was highly correlated with stem and soil water potentials. The highest midday stem water potential was lower than values commonly reported for nonstressed trees, and was accompanied by high soil water potential, indicating that the maximal water absorption rate of the root system under those particular soil conditions was limited. Stomatal conductance was highly correlated with leaf water potential (r 2 = 0.54), but a much better correlation was found with stem water potential (r 2 = 0.80). Stomatal conductance decreased at stem water potentials less than -2.1 MPa. Both stem water potential and stomatal conductance were unaffected by crop load under a wide range of irrigation rates.