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  • 1
    Language: English
    In: Applied and environmental microbiology, 01 January 2018, Vol.84(1)
    Description: Soil and plant inoculation with heterotrophic zinc-solubilizing bacteria (ZSB) is considered a promising approach for increasing zinc (Zn) phytoavailability and enhancing crop growth and nutritional quality. Nevertheless, it is necessary to understand the underlying bacterial solubilization processes to predict their repeatability in inoculation strategies. Acidification via gluconic acid production remains the most reported process. In this study, wheat rhizosphere soil serial dilutions were plated on several solid microbiological media supplemented with scarcely soluble Zn oxide (ZnO), and 115 putative Zn-solubilizing isolates were directly detected based on the formation of solubilization halos around the colonies. Eight strains were selected based on their Zn solubilization efficiency and siderophore production capacity. These included one strain of , two of , three strains of , one of , and one strain of In ZnO liquid solubilization assays, the presence of glucose clearly stimulated organic acid production, leading to medium acidification and ZnO solubilization. While solubilization by and was attributed to the accumulated production of six and seven different organic acids, respectively, the other strains solubilized Zn via gluconic, malonic, and oxalic acids exclusively. In contrast, in the absence of glucose, ZnO dissolution resulted from proton extrusion (e.g., via ammonia consumption by strains) and complexation processes (i.e., complexation with glutamic acid in cultures of ). Therefore, while gluconic acid production was described as a major Zn solubilization mechanism in the literature, this study goes beyond and shows that solubilization mechanisms vary among ZSB and are strongly affected by growth conditions. Barriers toward a better understanding of the mechanisms underlying zinc (Zn) solubilization by bacteria include the lack of methodological tools for isolation, discrimination, and identification of such organisms. Our study proposes a direct bacterial isolation procedure, which prevents the need to screen numerous bacterial candidates (for which the ability to solubilize Zn is unknown) for recovering Zn-solubilizing bacteria (ZSB). Moreover, we confirm the potential of matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS) as a quick and accurate tool for the identification and discrimination of environmental bacterial isolates. This work also describes various Zn solubilization processes used by wheat rhizosphere bacteria, including proton extrusion and the production of different organic acids among bacterial strains. These processes were also clearly affected by growth conditions (i.e., solid versus liquid cultures and the presence and absence of glucose). Although highlighted mechanisms may have significant effects at the soil-plant interface, these should only be transposed cautiously to real ecological situations.
    Keywords: Maldi-Tof MS ; Biofortification ; Bioremediation ; Metal Solubilization ; Organic Acids ; Proton Extrusion ; Siderophores ; Wheat ; Zinc-Solubilizing Bacteria ; Rhizosphere ; Soil Microbiology ; Bacteria -- Metabolism ; Triticum -- Microbiology ; Zinc -- Metabolism
    ISSN: 00992240
    E-ISSN: 1098-5336
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  • 2
    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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  • 3
    Language: English
    In: Science of the Total Environment, 15 April 2014, Vol.478, pp.226-234
    Description: 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 5.7 million tU may be recoverable from phosphate rock reserves. In 2010, the recoverable tU from phosphate rock and phosphoric acid production may have been 15,000 tU and 11,000 tU, 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.
    Keywords: Uranium ; Phosphorus ; Energy Security ; Environmental Pollution ; Food Security ; Resources Conservation ; Environmental Sciences ; Biology ; Public Health
    ISSN: 0048-9697
    E-ISSN: 1879-1026
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  • 4
    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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  • 5
    Language: English
    In: Science of the Total Environment, 01 December 2017, Vol.599-600, pp.1330-1343
    Description: Zinc (Zn) deficiency in human populations depending on cereals as a main source of Zn is a global malnutrition problem. In this field study, we investigated the potential of green manure application to increase soil Zn availability and wheat grain Zn concentrations (biofortification) on a Luvisol with different long-term fertilizer management. We also studied cadmium (Cd), as wheat is a major contributor of this undesired non-essential element to human diets. Clover ( L.), mustard ( L.) or no green manure was grown on field plots which had been managed with farmyard manure or mineral fertilizers for 65 years in Switzerland. After green manure incorporation into the soil, spring wheat ( L.) was grown on all plots. The “diffusive gradients in thin films” (DGT) method and DTPA extraction were used to compare soil Zn and Cd availability among the treatments. In contrast to mustard, clover increased soil mineral nitrogen concentrations and wheat biomass; however, neither increased grain Zn concentrations. DGT-available Zn and Cd increased temporarily after both farmyard manure and mineral nitrogen fertilizer application. Higher DTPA-extractable soil Zn and Cd, lower wheat grain yields, but higher grain Zn concentrations were obtained with farmyard manure compared to mineral fertilizers, independent of the green manure treatment. Farmyard manure added Zn, Cd and organic matter that increased the soil binding capacity for Zn and Cd. The decomposition of clover residues caused higher wheat grain yields, but only marginally lower grain Zn concentrations. The absence of a stronger dilution of grain Zn was probably due to organic acid and nitrogen release from decomposing clover, which facilitated Zn uptake by wheat. The study revealed that both long- and short-term field management with organic matter alters soil Zn and Cd concentrations but that the long-term effects dominate their uptake by wheat, in Zn sufficient soil.
    Keywords: Bioavailability ; Biofortification ; Dgt ; Farmyard Manure ; Legume ; Non-Legume ; Environmental Sciences ; Biology ; Public Health
    ISSN: 0048-9697
    E-ISSN: 1879-1026
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  • 6
    Language: English
    In: Applied Microbiology and Biotechnology, 2018, Vol.102(12), pp.5265-5278
    Description: Cowpea N 2 fixation and yield can be enhanced by selecting competitive and efficient indigenous rhizobia. Strains from contrasting agro-ecologies of Kilifi and Mbeere (Kenya) were screened. Two pot experiments were established consisting of 13 Bradyrhizobium strains; experiment 1 (11 Mbeere + CBA + BK1 from Burkina Faso), experiment 2 (12 Kilifi + CBA). Symbiotic effectiveness was assessed (shoot biomass, SPAD index and N uptake). Nodule occupancy of 13 simultaneously co-inoculated strains in each experiment was analyzed by matrix-assisted laser desorption/ionization time of flight (MALDI-TOF) mass spectrometry (MS) to assess competitiveness. Strains varied in effectiveness and competitiveness. The four most efficient strains were further evaluated in a field trial in Mbeere during the 2014 short rains. Strains from bacteroids of cowpea nodules from pot and field experiments were accurately identified as Bradyrhizobium by MALDI-TOF based on the SARAMIS™ database. In the field, abundant indigenous populations 7.10 × 10 3 rhizobia g −1 soil, outcompeted introduced strains. As revealed by MALDI-TOF, indigenous strains clustered into six distinct groups (I, II, III, IV, V and VI), group III were most abundant occupying 80% of nodules analyzed. MALDI-TOF was rapid, affordable and reliable to identify Bradyrhizobium strains directly from nodule suspensions in competition pot assays and in the field with abundant indigenous strains thus, its suitability for future competition assays. Evaluating strain competitiveness and then symbiotic efficacy is proposed in bioprospecting for potential cowpea inoculant strains.
    Keywords: Bradyrhizobium ; Cowpea ; Symbiotic effectiveness ; Nodule occupancy ; Protein profile ; Bacteroid
    ISSN: 0175-7598
    E-ISSN: 1432-0614
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  • 7
    Language: English
    In: Biogeosciences, Jan 8, 2018, Vol.15(1), p.105
    Description: The exchange rate of inorganic phosphorus (P) between the soil solution and solid phase, also known as soil solution P turnover, is essential for describing the kinetics of bioavailable P. While soil solution P turnover (K.sub.m) can be determined by tracing radioisotopes in a soil-solution system, few studies have done so. We believe that this is due to a lack of understanding on how to derive K.sub.m from isotopic exchange kinetic (IEK) experiments, a common form of radioisotope dilution study. Here, we provide a derivation of calculating K.sub.m using parameters obtained from IEK experiments. We then calculated K.sub.m for 217 soils from published IEK experiments in terrestrial ecosystems, and also that of 18 long-term P fertilizer field experiments. Analysis of the global compilation data set revealed a negative relationship between concentrations of soil solution P and K.sub.m . Furthermore, K.sub.m buffered isotopically exchangeable P in soils with low concentrations of soil solution P. This finding was supported by an analysis of long-term P fertilizer field experiments, which revealed a negative relationship between K.sub.m and phosphate-buffering capacity. Our study highlights the importance of calculating K.sub.m for understanding the kinetics of P between the soil solid and solution phases where it is bioavailable. We argue that our derivation can also be used to calculate soil solution turnover of other environmentally relevant and strongly sorbing elements that can be traced with radioisotopes, such as zinc, cadmium, nickel, arsenic, and uranium.
    Keywords: Soil Phosphorus – Properties ; Chemical Kinetics – Models ; Biogeochemical Cycles – Models
    ISSN: 1726-4170
    ISSN: 17264189
    E-ISSN: 17264189
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  • 8
    Language: English
    In: Forest Ecology and Management, 2003, Vol.175(1), pp.413-423
    Description: In a field experiment, lasting two years, an intensive monitoring of the nitrate reductase activity (NRA) of Norway spruce fine roots was used to investigate the question of whether the NRA is suitable as an indicator for nitrogen availability in the soil. The treatments were a liquid complete fertilisation containing 70–100 kg N (64% as nitrate), simulating a high N input to the soil, a non-treated control, and a water treatment as an additional control. Another treatment was the application of wood ash, which recycled mainly basic cations back into the forest soil (Ca, Mg, K). This treatment caused a mineralisation pulse leading to a shift in nitrate concentration in the soil solution. The NRA of the fine roots was increased by the liquid fertilisation (averages 34% compared to control), but also by the water treatment (averages 28% more than control) and most by the wood ash treatment (averages 82% more than control). Nitrate concentrations in the soil solution were enhanced during the irrigation with the fertiliser. The pH was distinctly elevated in the soil solution by the ash, but also by the liquid fertiliser treatment. The soil solution applied to the water treated plots was not monitored, but results from an investigation of soil extracts revealed an elevated pH in the soil of the water treated plots as well. The pH of the soil solution was significantly correlated with the NRA in the fine roots, while a correlation between the nitrate concentration in the soil solution and the NRA was not significant. When taking the spatial heterogeneity of the soil nitrate into account, a correlation between the nitrate concentration of the soil extract and the root NRA was found. Although only a weak correlation between the NRA and the actual soil nitrate was observed, the NRA is assumed to reflect the nitrate conditions in the soil, possibly only in a time scale of months. As shown with the wood ash and water treatments, an elevated NRA can also be caused from other environmental parameters which can change the nitrate availability in the soil and uptake properties of the roots. The conclusion is that the NRA of fine roots as a marker for nitrate concentrations in the soil is not suitable on a regional and short-term scale in the field if other environmental parameters (e.g. the soil pH) are subjected to pronounced changes.
    Keywords: Fine Roots ; Picea Abies ; Nitrate Reductase Activity ; Fertilisation ; Wood Ash ; Soil Solution ; Forestry ; Biology
    ISSN: 0378-1127
    E-ISSN: 1872-7042
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  • 9
    Language: English
    In: Applied Soil Ecology, December 2014, Vol.84, pp.93-111
    Description: Soil chemistry and biota heavily influence crop plant growth and mineral nutrition. The stress-severity and optimal resource allocation hypotheses predict mutualistic symbiotic benefits to increase with the degree of metabolic imbalance and environmental stress. Using two cross-factorial pot experiments with the same biologically active calcareous soil, one time highly saline and nutrient-deficient, and the other time partially desalinated and amended with mineral soil fertilizer, we explored whether these general predictions hold true for zinc (Zn) nutrition of bread wheat in mycorrhizal symbiosis. Increased arbuscular mycorrhizal (AM) fungal root colonization positively correlated with plant Zn nutrition, but only when plants were impaired in growth due to salinity and nutrient-deficiency; this was particularly so in a cultivar-responsive to application of mineral Zn fertilizer. Evidence for direct involvement of AM fungi were positive correlations between Zn uptake from soil and frequency of fungal symbiotic nutrient exchange organelles, as well as the quantitative abundance of AM fungi of the genera and but not . Combined partial soil desalination and fertilization swapped the dominance ranking from spp. to spp. Positive growth, nitrogen, and Zn uptake responses to mycorrhization were contingent on moderate soil fertilization with ZnSO . In agreement with the predictions of the stress-severity and optimal resource allocation hypotheses, plants limited in growth due to chemically adverse soil conditions invested relatively more into AM fungi, as evident from heavier root colonization, and took up relatively more Zn and nitrogen in response to mycorrhization, than better growing and less mycorrhized plants. It thus appears that crop plant cultivar-dependent mycorrhization and Zn fertilizer-responsiveness may reinforce each other, provided that there is bioavailable Zn in soil and plant growth is impaired by suboptimal chemical soil conditions.
    Keywords: Indigenous Arbuscular Mycorrhizal Fungi (Glomeromycota) ; Marginal Land ; Mycorrhizal Benefit ; Nutrient Acquisition ; Zinc Utilization Efficiency ; Reciprocal Symbiotic Resource Trading ; Agriculture ; Biology ; Ecology
    ISSN: 0929-1393
    E-ISSN: 1873-0272
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  • 10
    In: FEMS Microbiology Ecology, 2016, Vol. 93(1)
    Description: Alkaline phosphatases such as PhoD and PhoX are important in organic phosphorus cycling in soil. We identified the key organisms harboring the phoD and phoX genes in soil and explored the relationships between environmental factors and the phoD- and phoX- harboring community structures across three land uses located in arid to temperate climates on two continents using 454-sequencing. phoD was investigated using recently published primers, and new primers were designed to study phoX in soil. phoD was found in 1 archaeal, 13 bacterial and 2 fungal phyla, and phoX in 1 archaeal and 16 bacterial phyla. Dominant phoD -harboring phyla were Actinobacteria, Cyanobacteria, Deinococcus-Thermus, Firmicutes, Gemmatimonadetes, Planctomycetes and Proteobacteria , while abundant phoX -harboring phyla were Acidobacteria, Actinobacteria, Chloroflexi, Planctomycetes, Proteobacteria and Verrucomicrobia. Climate, soil group, land use and soil nutrient concentrations were the common environmental drivers of both community structures. In addition, the phoX- harboring community structure was affected by pH. Despite differences in environmental factors, the dominant phyla in the phoD- harboring community remained similar in all samples, while the composition of phoX differed substantially between the samples. This study shows that the composition of phoD and phoX is governed by the same environmental drivers but that phoD and phoX occur partly in different phyla. Despite differences in environmental factors, the community composition of phoD alkaline phosphatase remained similar in all samples, while the composition of phoX alkaline phosphatase differed substantially between the samples.
    Keywords: 454 - Sequencing ; Alkaline Phosphatase ; Land Use ; Soil ; Organic Phosphorus ; Ph
    E-ISSN: 1574-6941
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