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  • Author or Editor: P. C. Andersen x
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Abstract

The effects of root anaerobiosis on root respiration and leaf conductance (kl) were determined in solution culture experiments. Respiration of feeder roots (<2 mm diameter) in air (21% O2) of Pyrus betulaefolia Bunge, Pyrus calleryana Decne, Pyrus communis L. (‘Old Home’ × ‘Farmingdale 97’) and Cydonia oblonga Mill. ‘Provence BA 29’ was reduced by no more than 50% after 21 days of anaerobiosis. In contrast, root respiration of Prunus persica (L.) Batsch ‘Lovell’ was reduced by 80% with anaerobiosis, whereas that of Salix discolor Muhl. increased. Reductions in kl with anaerobiosis generally were more pronounced than reduction in root respiration when measured in air. Respiration rates of aerobically or anaerobically treated pear roots were inhibited by 25% to 50% when incubated in 0.5% O2 compared to rates in air. More work is required in order to delineate the relationship of root respiration and kl with anaerobiosis.

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

Abstract

Three separate factorial experiments were designed to evaluate the effect of 10 adjuvants on net CO2 assimilation rate (A), leaf conductance to water vapor (g1), and transpiration rate (E) of pecan [Carya illinoensis (Wagenh.) C. Koch] ‘Elliott’, blueberry (Vaccinium ashei Reade) ‘Chaucer’, red top photinia (Photinia × Fraseri Dress), and azalea (Rhododendron × ‘Pink Ruffles’). Single applications of Bond, Leaf Act 80A, Nu-Film-17, Ortho X-77, Penetrator 3, Plyac, Sorba Spray ZNP, Sun Spray 7E, Triton CS-7, or Triton B-1956 at recommended rates did not affect A, g1, or E compared to a water spray. The main effect of plant species was highly significant in all three studies without adjuvant-species interactions. A significant adjuvant effect on A occurred with a second application of Nu-Film-17, Plyac, and Triton B-1956. The only significant effect, when treatments were analyzed separately by species, was that A of Plyac-treated blueberry was less than the control.

Open Access

The Cohesion Tension Theory, first in 1894 introduced by Dixon and Joly is the theory most often invoked to explain water movement in a transpiring plant. The pressure chamber technique has provided the strongest indirect evidence for this theory. However, controversy remains because 1) the necessary pressure gradients in xylem vessels have never been measured directly; 2) it is uncertain how continuous water columns under great tensions could persist in a metastable state for extended periods of time, and; 3) direct pressure probe measurements on individual xylem vessels have not been indicative of the extreme negative pressures obtained with the pressure chamber. Xylem fluid is an energy-limited resource containing the lowest available carbon (energy content = 2 to 15 J/cm3) of any plant tissue. However, many species of xylophagous leafhoppers subsist entirely on this dilute food source, despite the negative pressures thought to occur in xylem vessels. Carbon limitations of leafhoppers were underscored by 1) high feeding rates; 2) an unprecedented assimilation efficiency of organic compounds (i.e., >99%); 3) ammonotelism, and; 4) synchronization of feeding to optimum host nutrient content both seasonally and diurnally. The maximum tension that can be generated by the cibarial pumping mechanism of an insect based on anatomy and biochemistry is about 0.3 to 0.6 MPa, far below the purported xylem tensions occurring during most daylight hours. By contrast, we have shown that feeding has been usually independent of xylem tensions, as measured with a pressure chamber, and instead was a function of the amide content of xylem fluid. Moreover, the calculated net energy gain of insect feeding (or that contained within insect biomass) on xylem fluid of a given composition under a given tension have also been an a paradox. Experiments will be described that provide insight into the energetics of xylem fluid extraction.

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

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

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