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Lee Kalcsits, Gregory van der Heijden, Michelle Reid, and Katie Mullin

smaller surface area. As fruit matures and the diameter increases, the fruit becomes smooth. Here, we sought to test whether absorption efficiency of Ca sprays changes during fruit development using 44 Ca as a stable isotope tracer combined with fruit

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Qinglong Zhang and Patrick H. Brown

The characteristics and mechanisms of foliar Zn uptake and translocation in pistachio (Pistachio vera L.) and walnut (Juglans regia L.) were investigated using 68Zn labelling in both intact and detached leaves. Following washing, mature walnut and pistachio leaves retained 8% and 12% of the total Zn applied, respectively. About half of retained Zn (3.5% and 6.5% of total Zn respectively) was absorbed into the leaf and translocated outside the treated area. Leaf age affected the Zn absorption capacity of pistachio but not walnut. Immature pistachio leaves absorbed more Zn than mature leaves. The absorption of Zn by walnut leaves at high concentrations (7.5 to 15 mm Zn) was not significantly affected by the pH of the solution. In pistachio Zn absorption was greatest at pH 3.5 and declined as pH increased to 8.5. The uptake process was not affected by light or addition of metabolic inhibitors. Foliar leaf absorption was only slightly affected by changes in temperature with an average Q10 of 1.2 to 1.4. This study suggests that foliar Zn uptake is dominated by an ion exchange and/or diffusion process rather than an active one. This study also demonstrates the usefulness of stable isotope labelling in studies of foliar Zn absorption.

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Hadi Susilo, Ying-Chun Peng, and Yao-Chien Alex Chang

measured to the last microgram with a microbalance (Mettler Toledo, Columbus, OH). The packaged samples were sent to the Stable Isotope Facility at the University of California, Davis for total N and 15 N analysis, which was done using a PDZ Europa ANCA

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Qinglong Zhang and Patrick H. Brown

The distribution and transport of foliar applied Zn were determined for pistachio (Pistachio vera L.) seedlings and mature trees using stable 68Zn isotope. In seedlings, ≈5.4% of Zn adsorbed by the leaf was transported out of the treated leaves and this Zn was detected in all other plant parts to varying extent. In mature trees, the transport of Zn occurred both acropetally and basipetally within the leaflets with more basipetal movement; however, no significant amount of Zn was transported out of the treated leaflets during the first 10 days after application. The total percentage of Zn transported to other plant parts 20 days after application was significantly greater when Zn was applied to immature leaflets (6.5%) than to mature leaflets (2.1%), though the majority of the absorbed Zn remained within the treated leaflets. The limited mobility of foliar-absorbed Zn in pistachio may partially be attributed to the high binding capacity of leaf tissue for Zn.

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Marlene Ayala, Lorena Mora, and Joaquín Torreblanca

In sweet cherry, highly advanced dwarf combinations using ‘Gisela’ rootstocks promote higher productivity than do more vigorous combinations but require maintaining the leaf area to fruit area (LA:F) ratio. An experiment using double isotopic enrichment with 13C and 15N was carried out in 5-year-old ‘Bing’/‘GI 6’ trees in a commercial orchard located in Santa Cruz, Chile (34°39′S; 71°19′W), and characterized by a Mediterranean climate. Forty whole sweet cherry trees (TR1) trained as central axes were pruned in winter [July 20, 60 days before full bloom (DBFB)] and another 40 trees were left without pruning (TR2). A single 13CO2 pulse and 15N-urea application to the mature leaves of individual 4-year-old branches on trees of both TRs was carried out during stage III (SIII). Winter pruning reduced yield by 44%, improved fruit quality [i.e., size, weight, and soluble solids content (SSC)] and induced the growth of extension shoots (ES) (i.e., number, length, and LA). For both TRs, fruits were stronger sinks for 13C-photoassimilates and 15N than were ES. ES of pruned trees had higher sink strength than ES of unpruned trees. Pruned trees developed more ES that were longer and that had higher LA compared with the ES of unpruned trees.

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Hadi Susilo, Ying-Chun Peng, Shui-Cheng Lee, Yu-Chun Chen, and Yao-Chien Alex Chang

when studying use of N fertilizer using traditional methods. Nitrogen-14 and nitrogen-15 ( 15 N) are the two stable isotopes of N with atmospheric natural abundances of 99.6337% and 0.3663%, respectively. The latter is an important tracer element in

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D. Michael Glenn

-time basis at the leaf ( Parkinson et al., 1980 ) and whole canopy level ( Garcia et al., 1990 ; Wullschleger et al., 1998 ). Natural abundance, stable isotopic carbon ratios provide a means to evaluate an integration of WUE for periods of time from days to

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Eric J. Hanson

Foliar B sprays (500 mg·liter-1) had increased the B content of apple (Malus domestics Borkh), pear (Pyrus communis L.), plum (Prunus domestics L.), and cherry (Prunus cerasus L.) leaves 90%) to 185% 3 days after treatment. Boron levels in treated apple, pear, and plum leaves decreased to levels similar to nontreated leaves by 9 days after application, whereas cherry leaves required 33 days to approach levels in nontreated leaves. Movement of applied B was also studied by treating cherry leaves with B solutions enriched in the stable isotope, 10B. Isotope analysis indicated that applied B moved out of leaves and into subtending tissues. The highest concentrations of applied B were found in buds, followed by bark and wood.

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Steven A. Weinbaum

Our understanding of the quantities and seasonal patterns of nutrient uptake by mature fruit trees has been limited by the difficulties in working with the large woody biomass of these organisms, tree-to-tree variability, and the resolution to distinguish between recently acquired nutrient from the nutrient background of the tree. We have coupled the use of stable isotopes of nitrogen (N) with periodic whole-tree excavations and nutrient analyses during the year. Vegetative growth, reproductive growth, and nutrient storage in perennial tree parts during tree quiescence represent nutrient sinks. Data obtained using mature pistachio, prune, and walnut trees indicate that macronutrient accumulation in metabolic sinks is associated with increases in tree macronutrient uptake. These data are consistent with the concept that sink removal of phloem-mobile nutrients from vascular circulation may provide the stimulus to further uptake of the nutrient(s) sequestered. We propose that the recognition of those patterns can be used to increase the efficiency of tree nutrient recovery and utilization.

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Rawia El-Motaium and Patrick H. Brown

Boron toxicity is a wide spread problem especially in arid and semiarid areas of the world. Boron toxicity can result in yield loss of many crop plants, especially stone fruits which are sensitive to high boron concentration. This study was designed to follow the effect of Ca+2 supplementation on partitioning of B at the plant organ level (leaves, stem, roots) and the subcellular level (the cell wall) using the stable isotope 10B.

Results demonstrate that calcium supplementation reduced B accumulation in plum and peach leaves by 31% at the low level (0.25 mM) and by 12% at the high B level (0.50 mM). Results indicate an effect of Ca on the uptake and distribution of 10B between plant organs.

Symptoms of B toxicity in peach (Lovell) include stem die back, necrotic brown spots on the stem and gum formation on the nodes, whereas in plum (Mariana), stem die back and gum formation, as droplets, on the lower leave's surface were the main symptoms.