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- Author or Editor: S. A. Weinbaum x
Abortion of distillate flowers (PFA) in a protandrous cultivar of walnut (Juglans regia L. cv. Serr) was increased by N deficiency. Starch and N concentrations in wood of 2-year-old twigs decreased to minimal levels during abortion of distillate flowers. Nitrogen reserves in woody tissues were reduced by foliar N deficiency, as were concentrations of sugars and N in vacuum-extracted xylem sap. Abortive distillate flowers ceased growth before spur leaves reached 50% of full expansion. PFA may result from transient deficiencies of C and N during the spring flush of growth. Depletion of storage C and N was accentuated before maturation of distillate flowers in this cultivar by the metabolic demands of many catkins, spur growth, and leaf expansion.
The pattern of total nonstructural carbohydrate [starch and soluble sugars (TNC)] accumulation in strawberry (Fragaria ×ananassa Duch.) nursery runner plants, cv. Camarosa, was determined for three growing seasons. A similar study was conducted on `Selva', but for only one year. Growth, development and fruit production patterns of plants transplanted to growth chambers (GC) or fruiting fields were also evaluated. The experiments were carried out on plants propagated in high latitude (41°50' N) nurseries in California (Siskiyou County). Plants were sampled beginning late summer through early autumn and analyzed for dry mass (DM) and TNC. Plants from different digging dates were established in GC or fruit evaluation plots in Irvine, Calif. (33°39'N). Initial TNC concentration in storage tissues at the time of nursery digging increased steadily from the second week of September to the third week of October. Crown and root TNC concentration and content were correlated positively with the accumulation of chilling units (CU = hours ≤7.2 °C) in the nursery. Root TNC concentration consistently increased from 6% to 10% DM in `Camarosa' (a short-day cultivar), and from ∼4% to 14% DM in `Selva' (a day-neutral cultivar) from mid-September to the first week of October. The root TNC content increased ∼2.5 times in `Camarosa' and ∼3.7 times in `Selva' during the same period. Transplant growth, development, and fruiting pattern were affected by digging date. Root TNC concentration and content were more sensitive to CU accumulation than crown TNC concentration and content. Therefore, root sampling appeared to be more appropriate than crown sampling for assessing the carbohydrate status and optimal digging dates of strawberry nursery runner plants early in the fall.
The effects of ambient temperatures between 15° and 43°C were determined on net photosynthesis of ‘French’ prune (Prunus domestica L. cv. Agen) trees maintained under a non-limiting soil water supply. The temperature optimum for photosynthesis was about 30° and net CO2 assimilation decreased rapidly above 35° even when water vapor pressure differences (VPD) were only 5 to 10 mb. Leaf resistance (r1) remained very low (2 to 3 sec cm-1) although leaf temperature reached 47° and the leaf water potential (ψ) decreased to -25 bars. Thus, non-stomatal photosynthetic inhibition was responsible for the 80% decline in net CO2 assimilation. Canopy wetting prevented the decline in net CO2 assimilation by reducing leaf temperature 8° (vs. control) and maintaining the ψ 14 bars higher than the non-misted control.
Leaf resistance (r1) in fully exposed leaves of bud-failure (BF) sensitive subclones of 2 almond (Prunus amygdalus Batsch) cultivars was much greater than in leaves of non-BF-sensitive (normal) subclones of these cultivars. The differences in resistance were evident at ambient temperatures between 26° and 38°C, and temperatures of fully exposed leaves on BF-sensitive plants exceeded ambient temperature and averaged 5° higher than leaf temperature of normal plants. The difference between BF-sensitive and normal subclones was not apparent below 25° or above 39°. Increase in resistance preceded the development of abnormal growth patterns characteristic of the BF syndrome, and these differences may serve to identify BF sensitivity at incipient stages of the syndrome. Stress is accentuated in BF-sensitive clones between 26° and 38° because transpirational cooling is suppressed; however, the physio-chemical basis of BF sensitivity remains obscure.
Ground application of urea increased yields of ‘Nonpareil’ almond (Prunus amygdalus Batsch) by increasing the number of flowers per tree rather than by increasing blossom receptivity and percentage fruit-set. Hand pollination of flowers on caged limbs indicated that blossom receptivity declined between 3 and 6 days after anthesis.
Mature almond [Prunus dulcis (Mill) D.A. Webb] trees growing on light-(Delhi sand) and heavy-textured (Yolo silty clay loam) soils were fertilized with 15N-depleted ammonium sulfate at different times during the year to permit direct measurement of fertilizer N within the trees. The distribution of fertilizer N between vegetative and reproductive organs was monitored during both the year of application, 1980, and the subsequent year. The later that fertilizer N was applied during the season, the less fertilizer N was recovered in the fruit and leaves that year, and the greater its N contribution to these organs was the following year. Isotopic labeling of fruit and leaves appeared to be relatively unaffected by soil texture during the year of fertilizer application. During the subsequent year, however, the recovery of fertilizer N by fruit and leaves was 2-fold greater on the heavy-textured soil than on the light-textured soil. Recovery of labeled N in fruit was relatively low on both soil types following application of fertilizer during the dormant period. Isotopic N was recovered in fruit in both 1980 and 1981 and constituted about 20% to 28% of fruit N at most. About 25% of the applied N was removed in the fruit on the heavy-textured soil over a 2-year period. Up to 1 kg N per tree was removed annually in the harvested fruit.
Four adjacent heavily cropping 12-year-old `Petite d'Agen' prune (Prunus domestica L.) trees were selected, and two of the trees were defruited in late spring (28 May) after the spring growth flush and full leaf expansion. Trees received K daily through the drip-irrigation system, and 15N-depleted (NH4)2SO4 was applied twice between the dates of defruiting and fruit maturation. Trees were excavated at the time of fruit maturity (28 July) and fractionated into their component parts. The following determinations were made after tree excavation and sample processing: tree dry weight, dry weight distribution among the various tree fractions (fruit, leaves, roots, trunk, and branches), tree nutrient contents, within-tree nutrient distribution, total nonstructural carbohydrates (TNCs), and recovery of labeled N. Trees only recovered ≈3% of the isotopically labeled fertilizer N over the 6-week experimental period. Heavily cropping trees absorbed ≈9 g more K per tree (17% of total tree K content) during the 2-month period of stage III fruit growth than defruited trees. The enhanced K uptake in heavily cropping trees was apparently conditioned by the large fruit K demand and occurred despite greatly reduced levels of starch and TNCs relative to defruited trees. Fruit K accumulation in heavily cropping trees was accompanied by K depletion from leaves and perennial tree parts. Except for K, fruited and defruited trees did not differ in nutrient content.
To be useful for indicating plant water needs, any measure of plant stress should be closely related to some of the known short- and medium-term plant stress responses, such as stomatal closure and reduced rates of expansive growth. Midday stem water potential has proven to be a useful index of stress in a number of fruit tree species. Day-to-day fluctuations in stem water potential under well-irrigated conditions are well correlated with midday vapor-pressure deficit, and, hence, a nonstressed baseline can be predicted. Measuring stem water potential helped explain the results of a 3-year deficit irrigation study in mature prunes, which showed that deficit irrigation could have either positive or negative impacts on tree productivity, depending on soil conditions. Mild to moderate water stress was economically beneficial. In almond, stem water potential was closely related to overall tree growth as measured by increases in trunk cross-sectional area. In cherry, stem water potential was correlated with leaf stomatal conductance and rates of shoot growth, with shoot growth essentially stopping once stem water potential dropped to between −1.5 to −1.7 MPa. In pear, fruit size and other fruit quality attributes (soluble solids, color) were all closely associated with stem water potential. In many of these field studies, systematic tree-to-tree differences in water status were large enough to obscure irrigation treatment effects. Hence, in the absence of a plant-based measure of water stress, it may be difficult to determine whether the lack of an irrigation treatment effect indicates the lack of a physiological response to plant water status, or rather is due to treatment ineffectiveness in influencing plant water status. These data indicate that stem water potential can be used to quantify stress reliably and guide irrigation decisions on a site-specific basis.