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Abstract

The feasibility of supplying the total Ν requirement of young, non-bearing ‘French’ prune (Prunus domestica L.) trees with foliar-applied NO^- ₃ was assessed based on the amount of Ν absorbed following foliar application of ¹⁵N-enriched KNO₃ and the seasonal Ν requirement as estimated by the total Ν accumulated over the growing season. Based on these data, 2-year-old prune trees would require more than 140 applications of 1.2% KNO₃ per year to maintain normal growth if foliar NO^- ₃ was the only Ν source.

Abstract

The pistachio (Pistacia vera L.) industry in California is based largely on a single pistillate (i.e., nut-producing) cultivar (Kerman) supported by seedling rootstocks of P. atlantica Desf. Data were collected and analyzed for tree growth and productivity of 113 mature ‘Kerman’ trees/P. atlantica seedlings over two cycles of alternate bearing. Tree size as estimated by trunk cross-sectional area varied 4-fold among the trees analyzed; tree yields, averaged over 4 years, varied 8-fold within the plot, and cropping efficiency (yield/cm² of trunk cross-sectional area) varied 3-fold among the trees within the orchard. The severity of alternate bearing also was calculated. Eight superior trees were identified within the orchard that not only had higher average yields and cropping efficiencies, but also exhibited much more regular cropping patterns (i.e., reduced severity of alternate bearing) than adjacent trees and the orchard as a whole.

The relationship between nitrogen (N) status and N uptake capacity has not been assessed in fruit trees. Determination of root uptake capacity by depletion of unlabeled N from external solution is less costly than methods using ¹⁵N, but is reportedly not suited for excised root studies due to reductions in uptake rates with time (Pearcy, R.W. et al. (eds). 1989. Plant Physiological Ecology, p. 195. Chapman and Hall. New York.). We tested two hypotheses: I) excised peach root NH₄₊ uptake rates are constant over several hours exposure to NH₄₊ solution and 2) excised peach root NH₄₊ uptake rates are negatively correlated with tree N status. Mature, N deficient, field grown `O'Henry' trees on `Lovell' peach (Prunus persica L. Batch.) rootstocks and growing in Winters, CA received (NH₄)₂SO₄ at a rate of 200 kg N/ha on September 29, 1993. An equal number of control trees received no N fertilizer. Foliar N deficiency symptoms of fertilized trees disappeared within 3 weeks of fertilization. On Nov. 9, 1993 (prior to leaf fall), excised roots were obtained from two fertilized and two unfertilized trees. Root NH₄₊ accumulation rates per unit root dry weight or root length were constant over 5 hours of exposure to 70 μM NH₄₊ (initial concentration) for both fertilized and unfertilized trees. Unfertilized tree root NH₄₊ uptake rates were significantly greater than those of fertilized trees on a root dry weight or length basis. Excised root NH₄₊ uptake may prove to be a sensitive index of fruit tree N status.

Abstract

Immature fruit of ‘French’ prune were treated in air or ethylene and mesocarp tissues incubated with crude cell wall degrading enzymes to release cells and protoplasts. Ethylene treatment substantially reduced the release of cells and protoplasts and increased the proportion of pectic polymers in the cell walls.

Extractable soil N may be leached below the plant rooting zone. and into the ground water. Orchards devoid of actively growing winter cover crops are subject to the greatest risk of NO_3- leaching during tree dormancy in California. We examined the patterns of KCl extractable NH₄₊ and NO_3-. and potentially mineralizable N (PMN) in the top 10 cm of soil across transects (60 samples, 150 m) in 3 almond orchard systems at 5 phenological stages in 1993. Extractable N was affected both spatially and temporally by management practices (e.g. herbicide or fertilizer application) and soil temperature. PMN did not exhibit local spatial patterns; geostatistical analysis revealed a trend across the transects indicating a larger scale of soil variation. possibly resulting from land leveling. The conventionally-managed orchard without a cover crop demonstrated higher levels of extractable NH₄₊ and NO_3- in the top 10 cm in Feb. and Nov. 1993, compared with orchards managed with organic fertilizers and winter cover crops.

Abstract

Fruiting branches of French prune (Prunus domestica L.) were exposed to ethylene or the ethylenegenerating (2-chloroethyl)phosphonic acid (ethephon) and subsequently ¹⁴C-uptake and ion leakage patterns of excised mesocarp disks were determined. Ion leakage was increased by these treatments, and the magnitudes of variances associated with ethephon-treated samples indicated differences in sensitivity among treated fruit. Under laboratory conditions electrolyte loss was associated with senescence of mesocarp tissue but was not a prerequisite of fruit abscission.

Abstract

Mature almond trees [Prunus dulcis (Mill) D.A. Webb] growing on a very light-textured (Delhi sand) soil were fertilized with ¹⁵N-depleted ammonium sulfate during 1980. Although uptake of labeled N from the soil N pool had ceased by 1982, label persisted within the trees at least until 1984. This label presumably represented the residual portion of the organic pool of storage N absorbed by the trees several years before. Leaf, pericarp, and embryo (kernel) samples were collected over a 2-month period during embryo maturation, and samples were processed for mass spectrometric analysis. Total leaf N did not decrease during embryo maturation, but labeled N in leaves decreased by 25%. These data are consistent with the concept of N turnover and flux through mature leaves and transport of N from leaves to fruit. These data indicate also that the N stored overwinter in perennial tissues of almond trees is redistributed within the trees throughout the growing season to support the development and function of annual plant organs such as leaves and fruit.

Abstract

Abscisic acid (ABA) and its water soluble glucoside diffused from leaves through petioles and along the axes of seedlings of tea crabapple (Malus hupehensis, Rehd.). The apparent mobility of the glucoside was considerably greater than that of free ABA. Concentrations of extractable and diffusible ABA were greatest in growing shoot tips. ABA from mature leaves diffused down the petiole more readily than from younger leaves. The enhanced liberation of inhibitor from older leaves may result in greater quantities of mobile ABA as the season progresses.

Abstract

Dry matter accumulation by immature ‘French’ prune (Prunus domestica L. cv Agen) fruit was reduced significantly within 7 days by (A) branch girdling plus defoliation (G+D), or (B) 300 ppm ethephon. Ethephon, but not G+D, reduced fruit removal force (FRF) significantly over the same interval. These data do not support the hypothesis that ethylene (C₂H₄)-induced thinning is initiated by assimilate deprivation. We propose that reduced mobilization of assimilates by ethephon-treated fruit is a consequence of the incipient fruit senescence which precedes abscission rather than the causative factor.

The interrelationships were studied between local soil N availability, tree N status, and \batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \(\mathrm{NO}_{3}^{-}\) \end{document} uptake capacity of excised roots of mature, commercially grown `O'Henry' peach trees. Nitrogen sufficient (+N) and deficient (–N) peach trees were established previously by differential N fertilization. High (+N) and low (–N) soil microsites were established under +N and –N trees in June 1994. Per unit root length \batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \(\mathrm{NO}_{3}^{-}\) \end{document} uptake capacities of roots excised from +N and –N microsites were measured in late July 1994. Root excised from +N microsites exhibited higher \batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \(\mathrm{NO}_{3}^{-}\) \end{document} uptake capacity per unit root length than roots from –N microsites irrespective of tree N status. The relationship of these data to the concept that \batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \(\mathrm{NO}_{3}^{-}\) \end{document} uptake is a function of sink N demand will be discussed.