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  • Article  (173)
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  • Article  (173)
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  • 1
    Language: English
    In: Chemosphere, 2011, Vol.84(6), pp.798-805
    Description: Harvests of crops, their trade and consumption, soil erosion, fertilization and recycling of organic waste generate fluxes of phosphorus in and out of the soil that continuously change the worldwide spatial distribution of total phosphorus in arable soils. Furthermore, due to variability in the properties of the virgin soils and the different histories of agricultural practices, on a planetary scale, the distribution of total soil phosphorus is very heterogeneous. There are two key relationships that determine how this distribution and its change over time affect crop yields. One is the relationship between total soil phosphorus and bioavailable soil phosphorus and the second is the relationship between bioavailable soil phosphorus and yields. Both of these depend on environmental variables such as soil properties and climate. We propose a model in which these relationships are described probabilistically and integrated with the dynamic feedbacks of cycling in the human ecosystem. The model we propose is a first step towards evaluating the large-scale effects of different nutrient management scenarios. One application of particular interest is to evaluate the vulnerability of different regions to an increased scarcity in mineral fertilizers. Another is to evaluate different regions’ deficiency in total soil phosphorus compared with the level at which they could sustain their maximum potential yield without external mineral inputs of phosphorus but solely by recycling organic matter to close the nutrient cycle.
    Keywords: Probabilistic Modeling ; Phosphorus Bioavailability ; Global Cycle ; Food Supply ; Chemistry ; Ecology
    ISSN: 0045-6535
    E-ISSN: 1879-1298
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  • 2
    In: Molecular Ecology, February 2014, Vol.23(3), pp.733-746
    Description: Interactions between arbuscular mycorrhizal fungal () species cocolonizing the same host plant are still little understood in spite of major ecological significance of mycorrhizal symbiosis and widespread occurrence of these fungi in communities rather than alone. Furthermore, shifting the composition of communities has demonstrated consequences for the provision of symbiotic benefits to the host as well as for the qualities of ecosystem services. Therefore, here we addressed the nature and strength of interactions between three different species in all possible two‐species combinations on a gradient of inoculation densities. Fungal communities were established in pots with plants, and their composition was assessed with taxon‐specific real‐time markers. Nature of interactions between the fungi was varying from competition to facilitation and was influenced by both the identity and relative abundance of the coinoculated fungi. Plants coinoculated with and grew bigger and contained more phosphorus than with any of these two fungi separately, although these fungi obviously competed for root colonization. On the other hand, plants coinoculated with and , which facilitated each other's root colonization, grew smaller than with any of these fungi separately. Our results point to as yet little understood complexity of interactions in plant‐associated symbiotic fungal communities, which, depending on their composition, can induce significant changes in plant host growth and/or phosphorus acquisition in either direction.
    Keywords: Barrel Medic ; Claroideoglomus Claroideum ; Functional Complementarity ; Gigaspora Margarita ; Quantitative Real‐Time ; Rhizophagus Irregularis
    ISSN: 0962-1083
    E-ISSN: 1365-294X
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  • 3
    Language: English
    In: Plant and Soil, 2011, Vol.339(1), pp.231-245
    Description: Diversity in phosphorus (P) acquisition strategies was assessed among three species of arbuscular mycorrhizal fungi (AMF) isolated from a single field in Switzerland. Medicago truncatula was used as a test plant. It was grown in a compartmented system with root and root-free zones separated by a fine mesh. Dual radioisotope labeling ( 32 P and 33 P) was employed in the root-free zone as follows: 33 P labeling determined hyphal P uptake from different distances from roots over the entire growth period, whereas 32 P labeling investigated hyphal P uptake close to the roots over the 48 hours immediately prior to harvest. Glomus intraradices , Glomus claroideum and Gigaspora margarita were able to take up and deliver P to the plants from maximal distances of 10, 6 and 1 cm from the roots, respectively. Glomus intraradices most rapidly colonized the available substrate and transported significant amounts of P towards the roots, but provided the same growth benefit as compared to Glomus claroideum , whose mycelium was less efficient in soil exploration and in P uptake and delivery to the roots. These differences are probably related to different carbon requirements by these different Glomus species. Gigaspora margarita provided low P benefits to the plants and formed dense mycelium networks close to the roots where P was probably transiently immobilized. Numerical modeling identified possible mechanisms underlying the observed differences in patterns of mycelium growth. High external hyphal production at the root-fungus interface together with rapid hyphal turnover were pointed out as important factors governing hyphal network development by Gigaspora , whereas nonlinearity in apical branching and hyphal anastomoses were key features for G. intraradices and G. claroideum , respectively.
    Keywords: Arbuscular mycorrhiza ; Extraradical mycelium ; Functional diversity ; Hyphal growth model ; Medicago truncatula ; Phosphorus
    ISSN: 0032-079X
    E-ISSN: 1573-5036
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  • 4
    Language: English
    In: Science of the Total Environment, 15 August 2014, Vol.490, pp.694-707
    Description: Despite evidence against imminent global phosphate rock depletion, phosphorus (P) scarcity scenarios and the subsequent consequences for global food security continue to be a matter of controversy. We provide a historicizing account to evaluate the degree and relevance of past human experiences with P scarcity. Using more than 80 literature sources, we trace the origin of the P scarcity concept and the first accounts of concerns; we report on three cases of scarcity discourse in the U.S. and revisit the concept of future resources. In addition, we present past evaluations of phosphate rock reserves and lifetime estimates for the world, the U.S., Morocco, and the Western Sahara, as well as past attempts to model phosphorus supply or collect information on phosphate rock. Our results show that current concerns have a long legacy and knowledge base to draw from and that promulgating the notion of depletion is inconsistent with past findings. We find that past depletion concerns were refuted by means of new resource appraisals, indicating that the supply was substantially larger than previously thought. Moreover, recommendations for national P conservation policies and other practices seem to have found little implementation. We demonstrate the merit of historic literacy for social learning and the weakness of the current P sustainability debate because it does not include this past knowledge.
    Keywords: Peak Phosphorus ; Food Security ; Phosphorus Sustainability ; Resources Scarcity ; Environmental History ; Environmental Sciences ; Biology ; Public Health
    ISSN: 0048-9697
    E-ISSN: 1879-1026
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  • 5
    Language: English
    In: The Science of the Total Environment, April 15, 2014, Vol.478, p.226(9)
    Description: To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.scitotenv.2014.01.069 Byline: Andrea E. Ulrich, Ewald Schnug, Horst-Michael Prasser, Emmanuel Frossard Abstract: This study seeks to identify and specify the components that make up the prospects of U recovery from phosphate rock. A systems approach is taken. The assessment includes i) reviewing past recovery experience and lessons learned; ii) identifying factors that determine recovery; and iii) establishing a contemporary evaluation of U endowments in phosphate rock reserves, as well as the available and recoverable amounts from phosphate rock and phosphoric acid production. We find that in the past, recovery did not fulfill its potential and that the breakup of the Soviet Union worsened then-favorable recovery market conditions in the 1990s. We find that an estimated 5.7milliontU may be recoverable from phosphate rock reserves. In 2010, the recoverable tU from phosphate rock and phosphoric acid production may have been 15,000tU and 11,000tU, respectively. This could have filled the world U supply-demand gap for nuclear energy production. The results suggest that the U.S., Morocco, Tunisia, and Russia would be particularly well-suited to recover U, taking infrastructural considerations into account. We demonstrate future research needs, as well as sustainability orientations. We conclude that in order to promote investment and production, it seems necessary to establish long-term contracts at guaranteed prices, ensuring profitability for phosphoric acid producers. Article History: Received 10 November 2013; Revised 16 January 2014; Accepted 19 January 2014
    Keywords: Phosphate Minerals -- Analysis ; Endowments -- Analysis ; Uranium -- Analysis ; Phosphates -- Analysis ; Phosphoric Acid -- Analysis
    ISSN: 0048-9697
    Source: Cengage Learning, Inc.
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  • 6
    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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  • 7
    Language: English
    In: Soil Biology and Biochemistry, July, 2014, Vol.74, p.21(10)
    Description: To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.soilbio.2014.02.014 Byline: Monika Welc, Emmanuel Frossard, Simon Egli, Else K. Bunemann, Jan Jansa Abstract: The abundance, distribution and functions of soil fungi in alpine ecosystems remain poorly understood. We aimed at linking the fungal community structure with soil enzymatic activities in the rhizospheres of several plants associating with mycorrhizal fungi (arbuscular, ecto- and ericoid) and growing along a soil developmental gradient on the forefield of an alpine glacier. Fungal communities in roots and in rhizosphere soils were assessed using a site-tailored set of quantitative PCR assays with fluorescent hydrolysis probes. Enzymatic activities of mycorrhizal roots and rhizosphere soils were assessed using fluorogenic substrates. In this study we addressed: i) whether and how the structure of fungal communities and enzymatic activities in rhizosphere soils change along the soil developmental gradient, ii) whether the type of mycorrhiza shows a clear relationship to the pattern of enzymatic activities in the rhizosphere, and iii) how the structure of fungal communities and enzymatic activities in rhizosphere soils is related to plant species abundances along the soil chronosequence. The results suggest that plant identity affected the structure of both ecto- and arbuscular mycorrhizal fungal communities in rhizosphere soil and roots, whereas the community of non-mycorrhizal fungi was rather dictated by the soil developmental stage. Both plant identity and associated mycorrhizal fungi affected the enzymatic activity in the rhizosphere soil. Species-specific elevations of rhizosphere enzyme activities were detected for Salix helvetica (chitinase and [alpha]-glucosidase), Rhododendron ferrugineum ([alpha]-glucosidase and sulfatase), and Agrostis gigantea (phosphatase and xylosidase). These results indicate different functional roles played by different types of mycorrhizal symbiosis in a young alpine ecosystem. Author Affiliation: (a) Swiss Federal Institute of Technology (ETH) Zurich, Institute of Agricultural Sciences, FMG C 18, Eschikon 33, 8315 Lindau, ZH, Switzerland (b) Swiss Federal Institute for Forest, Snow and Landscape Research (WSL), Zurcherstrasse 111, 8903 Birmensdorf, ZH, Switzerland (c) Institute of Microbiology, Academy of Sciences of the Czech Republic, VideAska 1083, 14220, Praha 4, KrA, Czech Republic Article History: Received 20 August 2013; Revised 17 February 2014; Accepted 20 February 2014
    Keywords: Alpine Ecosystems ; Enzymes ; Plants (Organisms) ; Hydrolysis
    ISSN: 0038-0717
    Source: Cengage Learning, Inc.
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  • 8
    Language: English
    In: The Science of the Total Environment, August 15, 2014, Vol.490, p.694(14)
    Description: To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.scitotenv.2014.04.050 Byline: Andrea E. Ulrich, Emmanuel Frossard Abstract: Despite evidence against imminent global phosphate rock depletion, phosphorus (P) scarcity scenarios and the subsequent consequences for global food security continue to be a matter of controversy. We provide a historicizing account to evaluate the degree and relevance of past human experiences with P scarcity. Using more than 80 literature sources, we trace the origin of the P scarcity concept and the first accounts of concerns; we report on three cases of scarcity discourse in the U.S. and revisit the concept of future resources. In addition, we present past evaluations of phosphate rock reserves and lifetime estimates for the world, the U.S., Morocco, and the Western Sahara, as well as past attempts to model phosphorus supply or collect information on phosphate rock. Our results show that current concerns have a long legacy and knowledge base to draw from and that promulgating the notion of depletion is inconsistent with past findings. We find that past depletion concerns were refuted by means of new resource appraisals, indicating that the supply was substantially larger than previously thought. Moreover, recommendations for national P conservation policies and other practices seem to have found little implementation. We demonstrate the merit of historic literacy for social learning and the weakness of the current P sustainability debate because it does not include this past knowledge. Article History: Received 9 January 2014; Revised 14 April 2014; Accepted 14 April 2014 Article Note: (miscellaneous) Editor: Charlotte Poschenrieder
    Keywords: Food Supply -- Analysis ; Phosphate Minerals -- Analysis ; Phosphates -- Analysis
    ISSN: 0048-9697
    Source: Cengage Learning, Inc.
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  • 9
    Language: English
    In: Soil Biology and Biochemistry, December 2014, Vol.79, pp.117-124
    Description: Crop production in subsistence agriculture in tropical Africa is still sustained mainly by short-to medium-term fallows to recuperate natural fertility of the soils. Microbes play a pivotal role both in the process of soil fertility restoration and in nutrient acquisition by the crops. Here we ask the question how the duration of fallow affects the composition of indigenous arbuscular mycorrhizal fungal (AMF) communities and their contribution to maize nutrition and growth, in acidic, low P soils of southern Cameroon. This question has been addressed in a bioassay where soils collected from continuously cropped fields, short-term fallows dominated by and long-term fallows (secondary forests) have been sterilized and back- and cross inoculated with living soils from the different land-use systems. Particular microbes larger than the pore size of the filter paper (mainly the fungi including the AMF) contained in the cropped and short-fallowed soils caused greater growth and P uptake stimulations to the maize as compared to the forest soil. By using molecular profiling, we demonstrated a shift in the composition of AMF communities along a gradient of fallow duration, changing from dominance by in the forest fallow soil, to dominance by under cropland. Our results contradict the hypothesis that deterioration of quality of root symbiotic communities would be responsible for a rapid yield decline following deforestation, and indicate a positive feedback of cropping on mycorrhizal functioning under conditions of shifting agriculture in tropical Africa.
    Keywords: Arbuscular Mycorrhiza ; Bioassay ; Chromolaena Odorata ; Fallow ; Maize ; Phosphorus ; Quantitative Real-Time Pcr ; Southern Cameroon ; Agriculture ; Chemistry
    ISSN: 0038-0717
    E-ISSN: 1879-3428
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  • 10
    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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