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  • 1
    Language: English
    In: Geochimica et Cosmochimica Acta, Jan 15, 2014, Vol.125, p.519(9)
    Description: To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.gca.2013.10.010 Byline: Christian von Sperber, Hajo Kries, Federica Tamburini, Stefano M. Bernasconi, Emmanuel Frossard Abstract: Plants and microorganisms under phosphorus (P) stress release extracellular phosphatases as a strategy to acquire inorganic phosphate (P.sub.i). These enzymes catalyze the hydrolysis of phosphoesters leading to a release of P.sub.i. During the enzymatic hydrolysis an isotopic fractionation (I[micro]) occurs leaving an imprint on the oxygen isotope composition of the released P.sub.i which might be used to trace phosphorus in the environment. Therefore, enzymatic assays with acid phosphatases from wheat germ and potato tuber and alkaline phosphatase from Escherichia coli were prepared in order to determine the oxygen isotope fractionation caused by these enzymes. Adenosine 5' monophosphate and glycerol phosphate were used as substrates. The oxygen isotope fractionation caused by acid phosphatases is 20-30a[degrees] smaller than for alkaline phosphatases, resulting in a difference of 5-7.5a[degrees] in [delta].sup.18O of P.sub.i depending on the enzyme. We attribute the enzyme dependence of the isotopic fractionation to distinct reaction mechanisms of the two types of phosphatases. The observed difference is large enough to distinguish between the two enzymatic processes in environmental samples. These findings show that the oxygen isotope composition of P.sub.i can be used to trace different enzymatic processes, offering an analytical tool that might contribute to a better understanding of the P-cycle in the environment. Article History: Received 2 May 2013; Accepted 6 October 2013 Article Note: (miscellaneous) Associate editor: Jon Chorover
    Keywords: Adenosine ; Glycerol ; Enzymes ; Phosphates ; Enzymology ; Hydrolysis
    ISSN: 0016-7037
    Source: Cengage Learning, Inc.
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  • 2
    Language: English
    In: Geochimica et Cosmochimica Acta, 2011, Vol.75(15), pp.4216-4227
    Description: Phosphorus (P) availability limits productivity in many ecosystems worldwide. As a result, improved understanding of P cycling through soil and plants is much desirable. The use of the oxygen isotopes associated to phosphate can be used to study the cycle of P in terrestrial systems. However, changes with time in the oxygen isotopes associated to available P have not yet been evaluated under field conditions. Here we present the variations in available-P oxygen isotopes, based on resin extractions, in a semi-arid site that included plots in which the amount of rainfall reaching the soil was modified. In addition, the oxygen isotopes in the less dynamic fraction which is extractable by HCl, were also measured. The δ O of the HCl-extractable phosphate shows no seasonal pattern and corresponds to the average value of the available phosphate of 16.5‰. This value is in the expected range for equilibration with soil water at the prevailing temperatures in the site. The δ O values of resin-extractable P showed a range of 14.5–19.1‰ (SMOW), and evidence of seasonal variability, as well as variability induced by rainfall manipulation experiments. We present a framework for analyzing the isotopic ratios in soil phosphate and explain the variability as mainly driven by phosphate equilibration with soil water, and by the isotopic effects associated with extracellular mineralization. Additional isotopic effects result from fractionation in uptake, and the input to the soil of phosphate equilibrated in leaves. These results suggest that the δ O of resin-extractable P is an interesting marker for the rate of biological P transformations in soil systems.
    Keywords: Geology
    ISSN: 0016-7037
    E-ISSN: 1872-9533
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  • 3
    In: New Phytologist, January 2013, Vol.197(1), pp.186-193
    Description: The objective of this study was to investigate the isotopic composition of oxygen bound to phosphate (δ18O‐PO4) in different phosphorus (P) pools in plant leaves. As a model plant we used soybean (Glycine max cv Toliman) grown in the presence of ample P in hydroponic cultures. The leaf blades were extracted with 0.3 M trichloroacetic acid (TCA) and with 10 M nitric acid. These extractions allowed measurement of the TCA‐soluble reactive P (TCA P) that is rapidly cycled within the cell and the total leaf P. The difference between total leaf P and TCA P yielded the structural P which includes organic P compounds not extractable by TCA. P uptake and its translocation and transformation within the soybean plants lead to an 18O enrichment of TCA P (δ18O‐PO4 between 16.9 and 27.5‰) and structural P (δ18O‐PO4 between 42.6 and 68.0 ‰) compared with 12.4‰ in the phosphate in the nutrient solution. δ18O values of phosphate extracted from soybean leaves grown under optimal conditions are greater than the δ18O‐PO4 values of the provided P source. Furthermore, the δ18O‐PO4 of TCA P seems to be controlled by the δ18O of leaf water and the activity of inorganic pyrophosphatase or other pyrophosphatases.
    Keywords: Acid Phosphatase ; Δo Of Leaf Water ; Δo‐ ; Soybean ; Structural P ; Tca‐Soluble Reactive P P
    ISSN: 0028-646X
    E-ISSN: 1469-8137
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  • 4
    Language: English
    In: Soil Biology and Biochemistry, December 2015, Vol.91, pp.298-309
    Description: The identification and quantification of different soil organic phosphorus (P) compounds is crucial for a better understanding of soil P dynamics. The aim of this study was to compare two commonly used characterisation methods: P NMR spectroscopy and enzyme addition assays (EAAs). The same 0.25 M NaOH and 0.05 M ethylenediaminetetraacetic acid (EDTA) extracts of ten temperate and tropical topsoils under arable crops or permanent grassland were analysed by each method. Additionally, the substrate specificity of the used enzymes was verified through P NMR analysis of one enzyme-treated soil extract. Finally, the molecular weight distribution of organic P was characterised using gel filtration chromatography. NaOH-EDTA extractable organic P ranged from 7 to 1108 mg P kg soil. Using P NMR spectroscopy, six organic P species in the mono- and diester region plus orthophosphate, pyrophosphate and phosphonates were detected. Deconvolution of P NMR spectra was not possible for two soils due to poor signal to noise ratio. Using EAAs, inositol phosphate-like P was identified as the largest enzyme-labile organic P class in most soils, followed by monoester-like P and DNA-like P. Corresponding classes of organic P determined by P NMR and EAAs were established and concentrations were found to agree well in general. However, repeatability was higher for P NMR spectroscopy than for EAAs. P NMR spectroscopy on an enzyme-treated extract showed that each enzyme acted on the anticipated organic P class, although treatment with phytase caused the appearance of a new and yet unidentified peak in the monoester region. Gel filtration chromatography of alkaline extracts revealed the presence of high-molecular weight organic P (〉5 kDa) which had a 1:1 relationship with enzyme-stable P. For both methods, advantages and drawbacks with respect to required sample pre-treatment, analysis time and cost and the total number of identifiable compounds are discussed. While EAAs are suitable for a quick and coarse characterisation of larger sample numbers, P NMR is more robust and allows a more detailed quantification of P forms.
    Keywords: Organic Phosphorus ; 31p NMR ; Enzyme Additions ; Method Comparison ; High Molecular Weight Compounds ; Agriculture ; Chemistry
    ISSN: 0038-0717
    E-ISSN: 1879-3428
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  • 5
    Language: English
    In: Water Research, 15 March 2017, Vol.111, pp.346-356
    Description: An essential aspect of eutrophication studies is to trace the ultimate origin of phosphate ions (P-PO ) associated with the solid phase of river sediments, as certain processes can make these ions available for algae. However, this is not a straightforward task because of the diversity of allochthonous and autochthonous sources that can supply P-PO to river sediments as well as the existence of in-stream processes that can change the speciation of these inputs and obscure the original sources. Here, we present the results of a study designed to explore the potentials, limitations and conditions for the use of the oxygen isotope composition of phosphate (δ Op) extracted from river sediments for this type of tracing. We first tested if the method commonly applied to soils to purify P-PO and to measure their δ Op concentrations could be adapted to sediments. We then applied this method to a set of sediments collected in a river along a gradient of anthropogenic pressure and compared their isotopic signatures with those from samples that are representative of the potential P-PO inputs to the river system (soils and riverbank material). The results showed that following some adaptations, the purification method could be successfully transposed to river sediments with a high level of P-PO purification (〉97%) and high δ Op measurement repeatability and accuracy (〈0.4‰). The values for the potential allochthonous sources varied from 11.8 to 18.3‰, while the δ Op value for the river sediments ranged from 12.2 to 15.8‰. Moreover, a sharp increase (〉3‰) in the sediment δ Op value immediately downstream from the discharge point revealed the strong impact of municipal wastewater. The calculation of the theoretical equilibrium δ O values using the river water temperature and δ O showed that the downstream sediments were in equilibrium, which was not the case for the upstream sediments. This difference could be related to the contrast between the short residence time of the transfer system in the catchment head, which can preserve the isotopic variability of the source materials, and the longer residence times and higher P bioavailability in the lower catchment, possibly fostering the recycling of P-PO by the biota and the equilibration of the oxygen isotope signature in P-PO . These results demonstrate the potential of the isotopic approach to assess the sources and in-stream turnover of sedimentary P in river systems.
    Keywords: Phosphorus Transfer ; Agriculture ; In-Stream Processes ; Eutrophication ; Phosphate Oxygen Isotopes ; Agriculture ; Engineering
    ISSN: 0043-1354
    E-ISSN: 1879-2448
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  • 6
    Language: English
    In: Geochimica et Cosmochimica Acta, 15 January 2014, Vol.125, pp.519-527
    Description: Plants and microorganisms under phosphorus (P) stress release extracellular phosphatases as a strategy to acquire inorganic phosphate (P ). These enzymes catalyze the hydrolysis of phosphoesters leading to a release of P . During the enzymatic hydrolysis an isotopic fractionation (ε) occurs leaving an imprint on the oxygen isotope composition of the released P which might be used to trace phosphorus in the environment. Therefore, enzymatic assays with acid phosphatases from wheat germ and potato tuber and alkaline phosphatase from were prepared in order to determine the oxygen isotope fractionation caused by these enzymes. Adenosine 5′ monophosphate and glycerol phosphate were used as substrates. The oxygen isotope fractionation caused by acid phosphatases is 20–30‰ smaller than for alkaline phosphatases, resulting in a difference of 5–7.5‰ in δ O of P depending on the enzyme. We attribute the enzyme dependence of the isotopic fractionation to distinct reaction mechanisms of the two types of phosphatases. The observed difference is large enough to distinguish between the two enzymatic processes in environmental samples. These findings show that the oxygen isotope composition of P can be used to trace different enzymatic processes, offering an analytical tool that might contribute to a better understanding of the P-cycle in the environment.
    Keywords: Geology
    ISSN: 0016-7037
    E-ISSN: 1872-9533
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  • 7
    Language: English
    In: Soil Biology and Biochemistry, November 2018, Vol.126, pp.64-75
    Description: Understanding the mechanisms underlying phosphorus (P) availability is important to predict forest productivity in a changing environment. We quantified P fluxes and traced P from plant litter into inorganic and organic soil P pools in organic horizons from two contrasting temperate forest soils with low and high inorganic P availability, respectively. We incubated the two organic horizons with and without litter after labelling the soil solution with P and performed sequential extractions at several time points in order to trace P dynamics in labile (water-extractable, available and microbial P) and non-labile (non-living organic P, P bound to iron and aluminium and P bound to calcium) pools. Under low P availability, P fluxes were dominated by gross P mineralization, and microbial P immobilization accounted for up to 95% of gross P mineralization. Additionally, labile P in plant litter was rapidly incorporated into microbial P and only a small fraction ended up in the non-labile inorganic P pools. In contrast, P fluxes under high P availability were dominated by abiotic processes, particularly by fast (within 10 days) sorption/desorption reactions between the available P and the P bound to aluminium. These findings support the hypothesis that under low P availability biological processes control P fluxes. The observed tight cycling of P, with little efflux due to net P mineralization, suggests that the mineralization of organic P is driven by microbial P demand, and that the microbial community could compete with plants for available P.
    Keywords: Radioisotope Tracing ; Sequential Extraction ; Mineralization ; 33p ; Isotopic Dilution ; Litter Addition ; Agriculture ; Chemistry
    ISSN: 0038-0717
    E-ISSN: 1879-3428
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  • 8
    Language: English
    In: Soil Science Society of America Journal, Jan-Feb, 2014, Vol.78(1), p.38(9)
    Description: Phosphorus is a major nutrient for all living organisms. In the terrestrial environment, P is considered a double-edged sword. In some areas, agricultural production is strongly limited by the low soil P availability, while in others, P inputs in excess of plant needs have resulted in pollution of water bodies. A better understanding of soil-plant P cycling is needed to provide agricultural and environmental managers with better concepts for P use. Together with the routine analysis of soil available P, the determination of P chemical forms, and the use of P radioisotopes, researchers have recently started using the ratio of stable oxygen isotopes in phosphate (?18O-P). The scientific community interested in using this isotopic tracer is slowly but steadily expanding because ?18O-P has proven to provide important information on biological processes influencing the P cycle and it could be used to trace the origin and fate of P in soil-plant systems. This review examines the published results and compiles the available data relevant for soiluplant systems, pinpoints gaps in analytical techniques and knowledge, and suggests key questions and topics to be investigated
    Keywords: Phosphorus (Chemical element) -- Research ; Phosphorus (Chemical element) -- Usage ; Phosphorus (Chemical element) -- Environmental Aspects ; Isotopes -- Research ; Soil Research
    ISSN: 0361-5995
    E-ISSN: 14350661
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  • 9
    Language: English
    In: Geoderma, 01 April 2018, Vol.315, pp.59-64
    Description: Forest clear-cuts may have severe effects on the soil structure and related nutrient cycling, though with yet unknown consequences for nutrient pools such as phosphorus (P) within microaggregates. We sampled the bulk mineral topsoil prior to clear cut as well as 1 and 2 years thereafter from the experimental forest site Wüstebach, Germany, and we assessed the degree of oxygen isotope exchange in HCl-extractable soil phosphate of two microaggregate size fractions (〈 20 μm, 20–250 μm) after incubating soil with O-labeled water. We found that after the clear-cut, microaggregate phosphates exchanged significantly more oxygen with the incubation water than before clear cut. One and two years after clear cut, the respective δ O values of soil phosphates (δ O ) were elevated by 16 and 38% (〈 20 μm) and by 43 and 53% (20–250 μm) than before the clear-cut, respectively, indicating that additional microaggregate P had been made available to biological P cycling. The degree of oxygen exchange after the clear-cut was significantly greater in larger soil microaggregates than in the smaller sized ones, reflecting that also at microaggregate level size controlled the increase in the bioavailability of P with changes in land management.
    Keywords: Forest Harvest ; P Turnover ; Cambisol ; 18o Labeling ; Agriculture
    ISSN: 0016-7061
    E-ISSN: 1872-6259
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  • 10
    Language: English
    In: Plant Methods, 01 September 2017, Vol.13(1), pp.1-12
    Description: Abstract Background Changing the phosphorus (P) nutrition leads to changes in plant metabolism. The aim of this study was to investigate how these changes are reflected in the distribution of 33P and the isotopic composition of oxygen associated to P (δ18OP) in different plant parts of soybean...
    Keywords: Δ18op of Tca P ; 33p ; Phosphorus ; Radioisotopes ; Soybeans ; Stable Isotopes ; Botany
    E-ISSN: 1746-4811
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