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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
    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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  • 3
    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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  • 4
    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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  • 5
    Language: English
    In: Plant and Soil, 2014, Vol.377(1), pp.439-456
    Description: Aims Phosphorus resources have to be managed sustainably and therefore the recycling of P from waste streams is essential. A thermo-chemical recycling process has been developed to produce a P fertilizer from sewage sludge ash (SSA) but its plant availability is unknown. Methods Two SSA products prepared with either Ca[Cl.sub.2] (SSACa) or Mg[Cl.sub.2] (SSAMg) as chemical reactant during the thermal treatment were mixed with three soils previously labeled with [sup.33]P. Reference treatments with water-soluble P added at equal amounts of total P were included. The transfer of P from SSACa and SSAMg to Lolium multiflorum or P pools of sequentially extracted soil-fertilizer incubations were quantified. Results The shoot P uptake from SSAMg was higher than from SSACa. For SSAMg the relative effectiveness compared to a water-soluble P fertilizer was 88 % on an acidic and 71 % on a neutral soil but only 4 % on an alkaline soil. The proportion of P derived from the fertilizer in the plant and in the first two extraction pools of soil-fertilizer incubations were strongly correlated, suggesting that it is sufficient to conduct an incubation study to obtain robust information on plant P availability. Conclusions We conclude that under acidic to neutral conditions SSAMg presents an appropriate alternative to conventional P fertilizers and the dissolution of P from SSAMg seems to be governed by protons and cations in the soil solution. Keywords Sewage sludge ash * [sup.33]P labeling * Recycling fertilizer * Radioisotopes * Italian ryegrass * Sequential extraction
    Keywords: Sewage sludge ash ; P labeling ; Recycling fertilizer ; Radioisotopes ; Italian ryegrass ; Sequential extraction
    ISSN: 0032-079X
    E-ISSN: 1573-5036
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  • 6
    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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  • 7
    Language: English
    In: Plant and Soil, 2011, Vol.341(1), pp.179-192
    Description: The integration of multipurpose legumes into low-input tropical agricultural systems is needed because they are a nitrogen (N) input through symbiotic fixation. The drought-tolerant cover legume canavalia ( Canavalia brasiliensis ) has been introduced for use either as forage or as a green manure into the crop-livestock system of the Nicaraguan hillsides. To evaluate its impact on the subsequent maize crop, an in-depth study on N dynamics in the soil-plant system was conducted. Microplots were installed in a 6-year old field experiment with maize-canavalia rotation. Direct and indirect 15 N-labelling techniques were used to determine N uptake by maize from canavalia residues and canavalia-fed cows’ manure compared to mineral fertilizer. Litter bags were used to determine the N release from canavalia residues. The incorporation of N from the amendment into different soil N pools (total N, mineral N, microbial biomass) was followed during the maize cropping season. Maize took up an average of 13.3 g N m −2 , within which 1.0 g N m −2 was from canavalia residues and 2.6 g N m −2 was from mineral fertilizer, corresponding to an amendment N recovery of 12% and 32%, respectively. Recoveries in maize would probably be higher at a site with lower soil available N content. Most of the amendment N remained in the soil. Mineral N and microbial N were composed mainly of N derived from the soil. Combined total 15 N recovery in maize and soil at harvest was highest for the canavalia residue treatment with 98% recovery, followed by the mineral fertilizer treatment with 83% recovery. Despite similar initial enrichment of soil microbial and mineral N pools, the indirect labelling technique failed to assess the N fertilizer value of mineral and organic amendments due to a high N mineralization from the soil organic matter.
    Keywords: Canavalia brasiliensis ; N ; Indirect and direct labelling techniques ; Microplot study ; Organic amendments
    ISSN: 0032-079X
    E-ISSN: 1573-5036
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  • 8
    Language: English
    In: PLoS ONE, 2011, Vol.6(12), p.e27825
    Description: Arbuscular mycorrhizal fungi (AMF) are known for their beneficial effects on plants. However, there is increasing evidence that some ruderal plants, including several agricultural weeds, respond negatively to AMF colonization. Here, we investigated the effect of AMF on the growth of individual weed species and on weed-crop interactions. ; First, under controlled glasshouse conditions, we screened growth responses of nine weed species and three crops to a widespread AMF, . None of the weeds screened showed a significant positive mycorrhizal growth response and four weed species were significantly reduced by the AMF (growth responses between −22 and −35%). In a subsequent experiment, we selected three of the negatively responding weed species – , and – and analyzed their responses to a combination of three AMF (, and ). Finally, we tested whether the presence of a crop (maize) enhanced the suppressive effect of AMF on weeds. We found that the growth of the three selected weed species was also reduced by a combination of AMF and that the presence of maize amplified the negative effect of AMF on the growth of . ; Our results show that AMF can negatively influence the growth of some weed species indicating that AMF have the potential to act as determinants of weed community structure. Furthermore, mycorrhizal weed growth reductions can be amplified in the presence of a crop. Previous studies have shown that AMF provide a number of beneficial ecosystem services. Taken together with our current results, the maintenance and promotion of AMF activity may thereby contribute to sustainable management of agroecosystems. However, in order to further the practical and ecological relevance of our findings, additional experiments should be performed under field conditions.
    Keywords: Research Article ; Agriculture ; Biology ; Plant Biology ; Biotechnology ; Ecology
    E-ISSN: 1932-6203
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  • 9
    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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  • 10
    Language: English
    In: Soil Biology and Biochemistry, July 2014, Vol.74, pp.21-30
    Description: 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 (chitinase and α-glucosidase), (α-glucosidase and sulfatase), and (phosphatase and xylosidase). These results indicate different functional roles played by different types of mycorrhizal symbiosis in a young alpine ecosystem.
    Keywords: Fungal Community ; Structure and Functions ; Mycorrhiza ; Rhizosphere ; Enzymes ; Salix Helvetica ; Agriculture ; Chemistry
    ISSN: 0038-0717
    E-ISSN: 1879-3428
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