Search Results

You are looking at 1 - 9 of 9 items for :

  • Author or Editor: P. C. Andersen x
  • Journal of the American Society for Horticultural Science x
Clear All Modify Search

Abstract

Net CO2 assimilation rate (A) and plant water relations of peach [Prunus persica (L.) Batsch cv. Flordaking] leaves were monitored during development under field conditions. Leaf conductance to water vapor (gl) and transpiration rate (E) of unfolding and expanding leaves approached maximum values before maximum A values were achieved. Net CO2 assimilation rate and water use efficiency (WUE) were greatest for recently expanded leaves and gradually declined with age after full expansion. Leaf water potential (ψw) was similar for all leaf ages under field conditions. Leaf dry weight/cm2 and chlorophyll/cm2 increased with leaf age after expansion. Diurnal patterns of gl, E, and ψw were similar for expanded spring- and summer-flush leaves. Midday ψw of −2.4 MPa (ψp = about 0.3 MPa) did not reduce gl. Expanding shoots had higher osmotic potentials (ψπ) and thus maintained lower turgor potentials (ψp) than fully expanded shoots. Shoot and leaf elongation rates were related exponentially to ψp and were reduced drastically below ψp 1.0 and 0.7 MPa, respectively. The bulk modulus of elasticity (є) increased linearly with ψp, but there were no significant differences in є of expanding and nonexpanding shoots. As leaf water deficits developed, shoot and leaf expansion were inhibited prior to gl or A. Thus, a moderate level of water stress can reduce the rate of vegetative growth of peach trees without concomitant reductions in carbon assimilation.

Open Access

Abstract

Spring- and summer-flush pecan [Carya illinoensis (Wangenh.) C. Koch] leaves were evaluated to determine climatological factors affecting leaf gas exchange, biophysical factors affecting growth, and to investigate the potential impact of a summer growth flush on alternate bearing. Expanding leaves had a higher osmotic potential, lower turgor pressure (ψp), poorer stomatal control, higher cuticular conductance, and a lower bulk modulus of elasticity than expanded leaves. Stomatal closure occurred at a progressively lower leaf water potential (ψw) as leaves aged. Net CO2 assimilation rate and leaf conductance to water vapor (g1) of pecan in the field did not decline in response to high atmospheric water stress and minimum midday ψw of −1.4 to −1.9 MPa when trees were supplied with adequate soil moisture. Leaf elongation rate was exponentially related to with marked reductions in growth occurring at ψp below 0.6 MPa and a complete cessation in growth below ψp = 0.3 MPa. Net CO2 assimilation rates of expanded leaves were up to 22 μmol·s−1m−2, several times higher than previously reported. Net CO2 assimilation rate was not inhibited by 41.5°C leaf temperature, 2000 μmol·s−1m−2 photosynthetic photon flux, and 3 kPa vapor pressure deficits (VPD). Transpiration rate (E) increased greatly with increasing VPD. Values of gl and E were generally higher than those reported for woody C3 perennials. The efficient water transport system of pecans under conditions of nonlimiting soil moisture may be a consequence of evolution in a floodplain ecosystem.

Open Access

Abstract

Volume flux (Jv), solute flux (Js), and the chemical profile of xylem exudate from cut shoots of ‘Noble’ and ‘Welder’ muscadine grapevines [Vitis rotundifolia (Michx.)] were analyzed as a function of temperature and temperature preconditioning. The effects of short-term (i.e., 2-hr) temperature changes on Jv, xylem fluid osmotic potential (Ψs) and Js from bleeding ‘Noble’ grapevines were determined. The effects of 10 days of preconditioning temperature (4 to 8C or 22 to 28C) on ‘Noble’ and ‘Welder’ were monitored at 25C in relation to Jv, Ψs, Js and inorganic element, amino acid, organic acid, and sugar composition of xylem fluid. Short-term temperature changes induced marked increases in Jv (Q10 = 2.0) and Js but little alteration in Ψs. Temperature-preconditioning effects were cultivar-dependent. Js was enhanced ≈2-fold for both cultivars when preconditioned at 22 to 28C. The stimulation in Js of ‘Noble’ was a result of increased solute concentration (reduced Ψs); increased Js of ‘Welder’ was associated with increased Jv. We propose that the increase in Js with a concomitant increase in Jv of ‘Welder’ was due to a change in hydraulic conductance. Conversely, the increase in Js of ‘Noble’ was due to an increased solute concentration in cells surrounding the xylem vessels and/or to changes in membrane permeability to solutes. Temperature preconditioning had a substantial effect on inorganic ion, amino acid, organic acid, and sugar profile in xylem exudate of ‘Noble’, yet the chemical profile of ‘Welder’ was not altered. The physiological basis for this cultivar-dependent preconditioning response is discussed.

Open Access

Abstract

A technique is described whereby osmotic potential, turgor potential and total fruit water potential can be determined quickly in the field with the aid of a pressure bomb, a hand held refractometer, and a percent soluble solids to osmotic potential conversion chart. A unique inverse linear relationship between percent soluble solids and osmotic potential was found for each fruit species. Application of this technique to rain cracking of ‘Napoleon’ sweet cherries (Prunus avium L.) shows that cracking is not strictly related to percent soluble solids, osmotic, turgor, or fruit water potential. This suggests that the degree of cuticular permeability, cuticular strength, cell wall strength or other factors may be of greater importance in determining cracking susceptibility than water potential parameters.

Open Access

Abstract

Potted seedlings and cuttings of various tree species were submerged to 5–10 cm above the soil level for up to 20 months in order to determine flood tolerance based on leaf conductance (kl), growth, and survival. Flooding induced a decline in kl at soil oxygen diffusion rates of 30, 22, 20, and 15 × 10−8g cm−2 min−1 for Prunus persica (L.) Batsch, Halford seedlings (peach), Pyrus communis L. cv. Bartlett (Bart), Pyrus calleryana Decne (Call), and Pyrus betulaefolia Bunge (Bet), respectively. The leaves of some species, particularly Pyrus communis L. cv. Old Home × Farmingdale 97 (OH × F 97), abscised shortly after a decline in kl, yet leaves of most other Pyrus species did not abscise despite months of maintaining a kl near zero. Growth rates were reduced for all fruit tree species except Bet and Call after one month of spring flooding. One month of fall flooding reduced the growth of all fruit tree species the following spring. Bet survived 20 months of continuous submergence; however, only Salix discolor Muhl. (willow) grew well under these conditions. Flooding promoted adventitious rooting of willow, Cydonia oblonga Mill. cv. Provence BA 29 (quince) and Malus domestica Borkh. cv. MM 106 (apple); anthocyanin pigmentation in leaves of apple and all Pyrus species; leaf chlorosis of quince, apple, and peach; and hypertrophied lenticels on the submerged stems and roots of all species. The tolerance, based upon kl, growth, and survival, was: willow > Bet > Call = quince > Bart > OH × F 97 = Pyrus pyrifolia (Burm.) Nak. (Pyri) = Pyrus ussuriensis Maxim. (Ussuri) = apple > peach. Although the survival of pear rootstocks with and without a ‘Bartlett’ scion were similar, flooding symptoms often were quite different.

Open Access

Leaf physiology and plant growth of Photinia x fraseri Dress were assessed when grown under full sunlight or (100% sun) or polypropylene shadecloth with a light transmittance of 69%, 47%, or 29% sun. Plants in 69% or 47% sun usually had the highest midday net CO2 assimilation rates (A). Net CO, assimilation rate was most dependent on photosynthetic photon flex (PPF R2 = 0.60), whereas stomata] conductance to water vapor was primarily influenced by vapor pressure deficit (R2 = 0.69). Stomatal conductance was often inversely related to sun level, and intercellular CO2 concentration was often elevated under 29% sun. Midday relative leaf water content and leaf water potential were unaffected by light regime. Light-saturated A was achieved at ≈ 1550 and 1150 μmol·m-2·s-1 for 100% and 29% sun-grown plants, respectively. Under 29% sun, plants had a lower light compensation point and a higher A at PPF < 1100 μmol·m-2·s-1. Total growth was best under 100% sun in terms of growth index (GI) increase, total leaf area, number of leaves, and dry weight (total, stem, leaf, and root), although plants from all treatments had the same GI increase by the end of the experiment. Plants in all treatments had acceptable growth habit (upright and well branched); however, plants grown in 29% sun were too sparsley foliated to be considered marketable. There were no differences in growth among the four treatments 7 months after the Photinia were transplanted to the field.

Free access

Leaf physiology and plant growth of Rhododendron × `Pink Ruffles' were compared under conditions of 100% sun and under polyethylene shadecloth with specifications of 69%, 47%, and 29% light transmittance. Net CO2 assimilation (A) and stomatal conductance to water vapor (gs) were often reduced for plants in the 100% sun regime, although few differences existed among the 69%, 47%, and 29% sun treatments. Stomatal conductance was very sensitive to leaf to air vapor pressure deficits (VPD), as evidenced by an 85% increase in gs with a decrease in VPD from 3.2 to 2.2 kPa. Light response curves established for plants after 54 days of exposure to 100% and 29% sun were similar, although A was consistently higher at all levels of photosynthetic photon flux for plants in the 29% sun regime. Maximum A was ≈5 and 6 μmol·m-2·s-1 for 100% and 29% sun-grown plants, respectively; light saturation occurred at ≈ 800 μmol·m-2·s-1 Midday relative leaf water content and leaf water potential were not affected by sun regime. The plant growth index decreased with increasing light level. Leaf, stem, and root dry weights; total leaf number and dry weight; total and individual leaf area; dry weight per leaf; and leaf chlorophyll concentration were reduced in 100% sun, yet few differences existed among the 69%, 47%, and 29% sun treatments. Shoot: root ratio and specific leaf weight were proportional to light level. Plants grown in the 100% sun regime were chlorotic and dwarfed, and plants in 29% sun were not sufficiently compact. One year after transplanting to the field under 100% sun, plants of all treatments were chlorotic and failed to grow.

Free access

Abstract

Drip irrigation applied to cultivars of rabbiteye blueberry (Vaccinium ashei Reade) maintained soil moisture at 25 to 35%, (volume basis), –0.07 bars soil-water potential while no irrigation resulted in 12.5% soil moisture, –2 to –3 bars. Irrigation reduced leaf diffusive resistance (rL) by 50% and increased transpiration (T) by 70% but had no significant effect on midday stem xylem pressure potentials (ψx ). Both yield and berry weight from irrigated plots were increased from 20 to 25% over those on nonirrigated plots. Seasonal changes in ψx , rL, and T of nonirrigated bushes suggested this species has some characteristic adaptations to drought conditions, one such adaptation being wax rodlets observed in and adjacent to stomatal pores. These may have contributed to a favorable water balance under stress by increasing leaf diffusive resistance.

Open Access

Abstract

Vapor Gard (VG), a polymer of β-pinene applied at concentrations of 1.5 or 2.5% (by volume to rabbit-eye blueberries (Vaccinium ashei Reade) influenced leaf temperatures, water balances, berry weight, and time of fruit harvest of plants with and without drip irrigation. A 2.5% VG spray uniformly covered entire leaves and increased midday xylem pressure potentials (Ψ×) by 50% and leaf resistances (r1) by 400%, decreased transpiration (T) by 80%, raised average leaf temperature by 2.2°C and resulted in phytotoxicity and leaf drop. A 1.5% spray did not significantly increase Ψx but doubled r1 and decreased Τ by 60% with no toxicity symptoms. When all cultivars are combined, the 1.5% spray applied to plants with and without irrigation increased berry weight by 31 and 17% but delayed berry maturation and decreased percentage total soluble solids of mature berries by 26 and 24%, respectively. Vapor Gard did not significantly change yields when used alone.

Open Access