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| 2. |
- Ahmed, Engy, et al.
(author)
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The Role of Microorganisms in the diversity and distribution of siderophores in Podzolic Forest Soil
- 2013
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In: Mineralogical magazine. - 0026-461X .- 1471-8022. ; 77:2, s. 161--208(48)
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Journal article (other academic/artistic)abstract
- Iron is a key component of the chemical architecture of the biosphere. Due to the low bioavailability of iron in the environment, microorganisms have developed specific uptake strategies. The most important one is the production of siderophores, which are operationally defined as low-molecular-mass biogenic Fe (III)-binding compounds which may greatly increase bioavailability of Fe [1]. One of the primary biogeochemical functions of siderophores is therefore to increase Fe bioavailability by promoting the dissolution of iron-bearing minerals [2]. This study aims to understand the role of microorganisms in the chemical diversity and distribution of siderophores in podzol soil and how this diversity can contribute to the bioavailability of Fe in forest soil.Soil samples were collected from an experimental site in the area of Bispgården in central Sweden (63°07′N, 16°70′E) from the O (organic), E (eluvial), B1 (upper illuvial), and C (mineral) horizons. Concentration and chemical composition of dissolved and adsorbed siderophores in the soil samples were determined using colorimetric assays and high-performance liquid chromatography.The highest siderophore concentrations were found in the O layer and thereafter decreased by depth. Concentrations of dissolved hydroxamate, catecholate and carboxylate siderophores were up to 84, 17 and 0.2 nmol/ g soil, respectively. In contrast, concentrations of adsorbed hydroxamates, catecholates and carboxylates were only up to 1.8, 3 and 0.2 nmol/ g soil, respectively.Siderophore-producing microorganisms were isolated from the same soil samples. Viable fungi, bacteria and actinomycete counts ranged from 7 to 300, from 300 to 1800, and from 0 to 5 cfu/gm, respectively. The highest counts were found in the O and E layers. Only the E layer contained the three types of siderophore-producing microorganisms investigated in this study. Siderophores were extracted from culture filtrates of the isolated microorganisms when grown under iron-limited conditions. These extracts varied considerably in siderophore composition. Fungal isolates produced up to 183 μM of hydroxamates, especially those isolated from the O layer, whereas bacteria and actinomycete isolated from the O and E layers of the soil produced high amounts of carboxylate, catecholate and hydroxamate siderophores. Actinomycete produced up to 93 μM of hydroxamates and 47 μM of catecholates, while bacteria produced up to 34 μM of carboxylates and up to 14 μM of catecholates.The depth variability in concentration and chemical composition and the good correlation between abundance of siderophore-producing microorganisms and siderophore soil concentrations strongly suggest that these siderophore-producing microorganisms play an important role in the mobilization of iron in the podzol soil that may be important in iron availability to plants in forest environment.[1] Clay et al. (1981) Biochemistry 20, 2432-2436. [2] Duckworth et al. (2009) ChemGeol 260, 149-158.
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| 3. |
- Bonaglia, Stefano, et al.
(author)
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EFFECT OF MEIOFAUNA ON BENTHIC ELEMENT CYCLING IN A BALTIC SEA COASTAL AREA
- 2013
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Conference paper (peer-reviewed)abstract
- We have studied the role of meiofaunal communities for nutrient cycling and organic matter mineralization in coastal sediments of the Baltic Sea. Although meiofauna is orders of magnitude more abundant than macrofauna and has commonly a much more diverse community structure, its importance for sediment biogeochemical pathways is poorly understood because of objective experimental difficulties when manipulating meiofauna communities due to small body sizes (0.04 to 1 mm) and inherent fragility. We used a density extraction method to separate intact and living metazoans from sediment and tested the effect of low meiofauna and high meiofauna abundances in the presence and absence of macrofauna for exchange rates of nutrients, O2, DIC, N2, and CH4. High abundances of meiofauna stimulated O2 uptake and the net N2 efflux by 16% and 34%, respectively, but did not change oxygen penetration depths significantly. By contrast, macrofauna increased oxygen penetration depths by 21% and stimulated methane emissions by a factor of 8. These results demonstrate the importance of meiofauna in the regulation of aerobic and anaerobic microbial processes and benthic fluxes in marine sediments.
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| 4. |
- Bonaglia, Stefano, et al.
(author)
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Effect of reoxygenation and Marenzelleria spp. bioturbation on Baltic Sea sediment metabolism
- 2013
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In: Marine Ecology Progress Series. - : Inter Research. - 0171-8630 .- 1616-1599. ; 482, s. 43-55
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Journal article (peer-reviewed)abstract
- Nutrient reduction and the improvement of bottom water oxygen concentrations are thought to be key factors in the recovery of eutrophic aquatic ecosystems. The effects of reoxygenation and bioturbation of natural hypoxic sediments in the Baltic Sea were studied using a mesocosm experiment. Anoxic sediment box cores were collected from 100 m depth in Kanholmsfjärden (Stockholm Archipelago) and maintained in flow-through mesocosms with 3 treatments: (1) hypoxic: supplied with hypoxic water; (2) normoxic: supplied with oxic water; and (3) Marenzelleria: supplied with oxic water and the polychaete Marenzelleria spp. (2000 ind. m–2). After a 7 wk long conditioning period, net fluxes of dissolved O2, CH4, Fe2+, Mn2+, NH4+, NO2-, NO3-, PO43- and H4SiO4, and rates of nitrate ammonification (DNRA), denitrification and anammox were determined. Phosphate was taken up by the sediment in all treatments, and the uptake was highest in the normoxic treatment with Marenzelleria. Normoxic conditions stimulated the denitrification rate by a factor of 5. Denitrification efficiency was highest under normoxia (50%), intermediate in bioturbated sediments (16%), and very low in hypoxic sediments (4%). The shift from hypoxic to normoxic conditions resulted in a significantly higher retention of NH4+, H4SiO4 and Mn2+ in the sediment, but the bioturbation by Marenzelleria reversed this effect. Results from our study suggest that bioturbation by Marenzelleria stimulates the exchange of solutes between sediment and bottom water through irrigation and enhances bacterial sulfate reduction in the burrow walls. The latter may have a toxic effect on nitrifying bacteria, which, in turn, suppresses denitrification rates.
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| 5. |
- Bonaglia, Stefano, et al.
(author)
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Meiofauna increases bacterial denitrification in marine sediments
- 2014
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In: Nature Communications. - : Springer Science and Business Media LLC. - 2041-1723. ; 5, s. 5133-
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Journal article (peer-reviewed)abstract
- Denitrification is a critical process that can alleviate the effects of excessive nitrogen availability in aquatic ecosystems subject to eutrophication. An important part of denitrification occurs in benthic systems where bioturbation by meiofauna (invertebrates <1mm) and its effect on element cycling are still not well understood. Here we study the quantitative impact of meiofauna populations of different abundance and diversity, in the presence and absence of macrofauna, on nitrate reduction, carbon mineralization and methane fluxes. In sediments with abundant and diverse meiofauna, denitrification is double that in sediments with low meiofauna, suggesting that meiofauna bioturbation has a stimulating effect on nitrifying and denitrifying bacteria. However, high meiofauna densities in the presence of bivalves do not stimulate denitrification, while dissimilatory nitrate reduction to ammonium rate and methane efflux are significantly enhanced. We demonstrate that the ecological interactions between meio-, macrofauna and bacteria are important in regulating nitrogen cycling in soft-sediment ecosystems.
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| 6. |
- Bonaglia, Stefano, et al.
(author)
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Seasonal benthic nutrient cycling in a Baltic sea estuary
- 2012
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Conference paper (other academic/artistic)abstract
- Decades of urban, industrial, and agricultural discharge of nitrogen and phosphorus to the Baltic Sea have contributed to the spreading of water column hypoxia and annual widespread cyanobacteria blooms. Central to mitigating Baltic Sea eutrophication is to resolve how much reduction strategies of external N and P loading are offset by internal loading of the Baltic through nutrient recycling from the sediment. We investigated the seasonal variation of benthic nitrogen and phosphorus cycling in an estuary of the Baltic impacted by decades of sewage discharge. Sediment nutrient fluxes, denitrification, Anammox, DNRA, potential nitrification, and total and diffusive oxygen uptake (TOU/DOU) were quantified with 15N-tracer methods and microsensor profiling. Data indicate benthic net efflux of ammonium and phosphorus during the summer months, decreasing N2 loss with increasing organic matter content, and benthic N/P regeneration with a ratio of 3 to 7 compared to the sewage discharge N/P of ≈ 25, and a significant contribution (6 to 25%) of Anammox to N2 loss. On average benthic denitrification and Anammox may reduce the N load to the estuary by up to 54%.
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| 7. |
- Bonaglia, Stefano, 1983-, et al.
(author)
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Seasonal oxygen, nitrogen and phosphorus benthic cycling along an impacted Baltic Sea estuary: regulation and spatial patterns
- 2014
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In: Biogeochemistry. - : Springer Science and Business Media LLC. - 0168-2563 .- 1573-515X. ; 119:1-3, s. 139-160
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Journal article (peer-reviewed)abstract
- The regulatory roles of temperature, eutrophication and oxygen availability on benthic nitrogen (N) cycling and the stoichiometry of regenerated nitrogen and phosphorus (P) were explored along a Baltic Sea estuary affected by treated sewage discharge. Rates of sediment denitrification, anammox, dissimilatory nitrate reduction to ammonium (DNRA), nutrient exchange, oxygen (O2) uptake and penetration were measured seasonally. Sediments not affected by the nutrient plume released by the sewage treatment plant (STP) showed a strong seasonality in rates of O2 uptake and coupled nitrification-denitrification, with anammox never accounting for more than 20% of the total dinitrogen (N2) production. N cycling in sediments close to the STP was highly dependent on oxygen availability, which masked temperature-related effects. These sediments switched from low N loss and high ammonium (NH4+) efflux under hypoxic conditions in the fall, to a major N loss system in the winter when the sediment surface was oxidized. In the fall DNRA outcompeted denitrification as the main nitrate (NO3-) reduction pathway, resulting in N recycling and potential spreading of eutrophication. A comparison with historical records of nutrient discharge and denitrification indicated that the total N loss in the estuary has been tightly coupled to the total amount of nutrient discharge from the STP. Changes in dissolved inorganic nitrogen (DIN) released from the STP agreed well with variations in sedimentary N2 removal. This indicates that denitrification and anammox efficiently counterbalance N loading in the estuary across the range of historical and present-day anthropogenic nutrient discharge. Overall low N/P ratios of the regenerated nutrient fluxes impose strong N limitation for the pelagic system and generate a high potential for nuisance cyanobacterial blooms.
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| 8. |
- Brüchert, Volker, 1965-, et al.
(author)
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BENTHIC BOUNDARY LAYER NUTRIENT AND OXYGEN BIOGEOCHEMISTRY IN A EUTROPHIED BALTIC SEA ESTUARY
- 2013
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Conference paper (peer-reviewed)abstract
- We present dissolved nutrient and oxygen concentrations determined with a benthic boundary layer profiling system for a set of stations along a eutrophication gradient in a Baltic Sea estuary. The sampling system yields vertically highly resolved CTD, oxygen, and nutrient profiles of the lowermost 80 cm of water overlying the sediment. Continuous oxygen and CTD measurements over 8 – 24 hours at fixed depths above the sediment surface provided information on the temporal variability of nutrients and the physical structure within the benthic boundary layer. These data indicate multiple short-term episodes of vertical mixing and stable stratification within the boundary layer that can lead to short-term fluctuations in bottom water oxygen of more than 100 µM. This high degree of temporal variability needs to be taken into account for benthic flux calculations that assume vertically mixed benthic boundary layers.
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| 9. |
- Brüchert, Volker, et al.
(author)
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Sediment med nyckelroll i näringsväven
- 2014
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In: Havsutsikt. - 1104-0513. ; 2014:1, s. 20-21
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Journal article (pop. science, debate, etc.)abstract
- I sedimenten sker processer som kan vara helt avgörande för näringsbalansen i havsvattnet. Omvandlingen av fosfor till olika former är relativt väl känd, medan detaljerna i kvävets kretslopp är betydligt mindre kända. Mer än hälften av den årliga tillförseln av kväve till Östersjön beräknas omsättas till kvävgas i sedimentet, vilket sedan går förlorat för de flesta marina organismer.
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