| 1. |
- Björk, Robert G., 1974, et al.
(author)
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Contrasting effects of wood ash application on microbial community structure, biomass and processes in drained forested peatlands
- 2010
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In: FEMS Microbiology Ecology. - : Oxford University Press (OUP). - 1574-6941 .- 0168-6496. ; 73:3, s. 550-562
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Journal article (peer-reviewed)abstract
- The effects of wood ash application on soil microbial processes were investigated in three drained forested peatlands, which differed in nutrient status and time since application. Measured variables included concentrations of soil elements and phospholipid fatty acids (PLFAs), net nitrogen mineralisation, nitrification and denitrification enzyme activity, potential methane oxidation, methane production and microbial respiration kinetics. Wood ash application had a considerable influence on soil element concentrations. This mirrored a decrease in the majority of the microbial biomarkers by more than one-third in the two oligotrophic peatlands, although microbial community composition was not altered. The decreases in PLFAs coincided with reduced net ammonification and net nitrogen mineralisation. Other measured variables did not change systematically as a result of wood ash application. No significant changes in microbial biomass or processes were found in the mesotrophic peatland, possibly because too little time (1 year) had elapsed since the wood ash application. This study suggests that oligotrophic peatlands can be substantially affected by wood ash for a period of at least four years after application. However, within 25 years of the wood ash application, the microbial biomass seemed to have recovered or adapted to enhanced element concentrations in the soil.
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| 2. |
- Ellegård, Lars, 1958, et al.
(author)
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Distinguishing vegan-, vegetarian-, and omnivorous diets by hair isotopic analysis.
- 2019
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In: Clinical nutrition. - : Elsevier BV. - 1532-1983 .- 0261-5614. ; 38:6, s. 2949-2951
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Journal article (peer-reviewed)abstract
- Dietary risks contribute heavily to disability-adjusted life years (DALYs), being more important than hypertension, obesity, or smoking. To measure dietary exposure remains a challenge in nutrition research.The aim of the present study was to test the hypothesis that isotope ratios of 15N and 13C in human hair could distinguish between subjects adhering to different habitual diets.20 male and 29 female subjects average 31 years old (range 19-53), with stable dietary habits volunteered. Diets were vegan, vegetarian and omnivorous. Hair samples were processed on an elemental analyser coupled to isotope-ratio mass spectrometry.δ15N differed between vegan, vegetarian and omnivorous diets, p<0.05 for all. δ13C differed between vegan and omnivorous diets, p<0.05, but neither of these diets were separated from the vegetarian diet.Elemental Analysis of δ13C and especially δ15N with isotope ratio mass spectrometry seems to be a promising, non-invasive and objective way to distinguish groups of subjects on different habitual diets, at least if n=>10.
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| 3. |
- Klemedtsson, Leif, 1953, et al.
(author)
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Skogaryd – Integration of terrestrial and freshwater greenhouse gas sources and sinks
- 2010
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In: 1st COST meeting ‘Belowground carbon in Europeanforest’, Birmensdorf, Switzerland, 26–28 January 2010..
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Conference paper (other academic/artistic)abstract
- Forests play an important role in the global carbon (C) cycle, and management as well as climate can cause major effects on the balance of C between the atmosphere and the plant/soil system. With re-gard to our commitments to the Kyoto and post-Kyoto actions on climate change, we need reliable predictions on how this balance is affected by management and climate. In 2006 the Skogaryd Research Forest was established in the southwest of Sweden (58°23’N, 12°09’E). The overall goal is to quantify net greenhouse gas (GHG) fluxes from drained spruce forest, by determining the individual fluxes and pools of C and nitrogen and elucidating their connection to site fertility, drainage status and abiotic parameters and then use the generated data in GHG models, for model validations and ultimately emissions predictions. During 2006-2009 the research has fo-cused on two sites, mineral and organic, dominated by Norway spruce (Picea abies). Both sites are drained fertile soils but with different land-use history that have affected their physical properties. Measurements includes: net ecosystem exchange of CO2, Shoot photosynthesis and respiration at different locations within the canopy, stem respiration, emissions of N2O and CH4 using manual cham-bers, soil respiration with automatic chambers including a trenching experiment where root-, mycelia-, and heterotrophic respiration are separated, fine root production using minirhizotrons, and mycelia production. The organic site also includes a wood ash experiment. From 2010 the research will be expanded to the whole watershed, from the mire system via streams, riparian zones, forests, to lakes and the subsequent exchange between the atmosphere and surface waters. Different terrestrial and limnic ecosystems will be linked holistically, using site specific tech-niques at different scales, from aircraft (km2) to chambers (m2) to create integrated models that can be used to quantify net GHG flux for management strategies.
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| 4. |
- Meyer, Astrid, et al.
(author)
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A fertile peatland forest does not constitute a major greenhouse gas sink
- 2013
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In: Biogeosciences. - : Copernicus GmbH. - 1726-4170 .- 1726-4189. ; 10, s. 7739-7758
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Journal article (peer-reviewed)abstract
- Afforestation has been proposed as a strategy to mitigate the often high greenhouse gas (GHG) emissions from agricultural soils with high organic matter content. However, the carbon dioxide (CO2) and nitrous oxide (N2O) fluxes after afforestation can be considerable, depending predominantly on site drainage and nutrient availability. Studies on the full GHG budget of afforested organic soils are scarce and hampered by the uncertainties associated with methodology. In this study we etermined the GHG budget of a spruce-dominated forest on a drained organic soil with an agricultural history. Two different approaches for determining the net ecosystem CO2 exchange (NEE) were applied, for the year 2008, one direct (eddy covariance) and the other indirect (analyzing the different components of the GHG budget), so that uncertainties in each method could be evaluated. The annual tree production in 2008 was 8.3±3.9 tC ha−1 yr−1 due to the high levels of soil nutrients, the favorable climatic conditions and the fact that the forest was probably in its phase of maximum C assimilation or shortly past it. The N2O fluxes were determined by the closed-chamber technique and amounted to 0.9±0.8 tCeq ha−1 yr−1. According to the direct measurements from the eddy covariance technique, the site acts as a minor GHG sink of −1.2±0.8 t Ceq ha−1 yr−1. This contrasts with the NEE estimate derived from the indirect approach which suggests that the site is a net GHG emitter of 0.6±4.5 tCeq ha−1 yr−1. Irrespective of the approach applied, the soil CO2 effluxes counter large amounts of the C sequestration by trees. Due to accumulated uncertainties involved in the indirect approach, the direct approach is considered the more reliable tool. As the rate of C sequestration will likely decrease with forest age, the site will probably become a GHG source once again as the trees do not compensate for the soil C and N losses. Also forests in younger age stages have been shown to have lower C assimilation rates; thus, the overall GHG sink potential of this afforested nutrient-rich organic soil is probably limited to the short period of maximum C assimilation.
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| 5. |
- Andresen, Louise C., 1974, et al.
(author)
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Amino acid and N mineralization dynamics in heathland soil after long-term warming and repetitive drought
- 2015
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In: Soil. - : Copernicus GmbH. - 2199-3971 .- 2199-398X. ; 1:1, s. 341-349
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Journal article (peer-reviewed)abstract
- Monomeric organic nitrogen (N) compounds such as free amino acids (FAAs) are an important resource for both plants and soil microorganisms and a source of ammonium (NH4+) via microbial FAA mineralization. We compared gross FAA dynamics with gross N mineralization in a Dutch heathland soil using a 15N tracing technique. A special focus was made on the effects of climate change factors warming and drought, followed by rewetting. Our aims were to (1) compare FAA mineralization (NH4+ production from FAAs) with gross N mineralization, (2) assess gross FAA production rate (depolymerization) and turnover time relative to gross N mineralization rate, and (3) assess the effects of a 14 years of warming and drought treatment on these rates. The turnover of FAA in the soil was ca. 3 h, which is almost 2 orders of magnitude faster than that of NH4+ (i.e. ca. 4 days). This suggests that FAA is an extensively used resource by soil microorganisms. In control soil (i.e. no climatic treatment), the gross N mineralization rate (10 ± 2.9 μg N g−1 day−1) was 8 times smaller than the total gross FAA production rate of five AAs (alanine, valine, leucine, isoleucine, proline: 127.4 to 25.0 μg N g−1 day−1). Gross FAA mineralization (3.4 ± 0.2 μg N g−1 day−1) contributed 34% to the gross N mineralization rate and is therefore an important component of N mineralization. In the drought treatment, a 6–29% reduction in annual precipitation caused a decrease of gross FAA production by 65% and of gross FAA mineralization by 41% compared to control. On the other hand, gross N mineralization was unaffected by drought, indicating an increased mineralization of other soil organic nitrogen (SON) components. A 0.5–1.5 °C warming did not significantly affect N transformations, even though gross FAA production declined. Overall our results suggest that in heathland soil exposed to droughts a different type of SON pool is mineralized. Furthermore, compared to agricultural soils, FAA mineralization was relatively less important in the investigated heathland. This indicates more complex mineralization dynamics in semi-natural ecosystems.
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| 6. |
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| 7. |
- Andresen, Louise C., 1974, et al.
(author)
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Depolymerization and mineralization – investigating N availability by a novel 15N tracing model
- 2016
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In: SOIL. - : Copernicus GmbH. - 2199-398X. ; 2:3, s. 433-442
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Journal article (other academic/artistic)abstract
- Depolymerization of soil organic matter such as proteins and peptides into monomers (e.g. amino acids) is currently thought to be the rate limiting step for N availability in terrestrial N cycles. The mineralization of free amino acids (FAA), liberated by depolymerization of peptides, is an important fraction of the total N mineralization. Accurate assessment 10 of peptide depolymerization and FAA mineralization rates is important in order to gain a better understanding of the N cycle dynamics. Due to the short time span, soil disturbance and unnatural high FAA content during the first few hours after the labelling with the traditional 15N pool dilution experiments, analytical models might overestimate peptide depolymerization rate. In this paper, we present an extended numerical 15N tracing model Ntrace which incorporates the FAA pool and related N processes in order to 1) provide a more robust and coherent estimation of production and mineralization rates of FAAs; 2) 15 and 2) suggest an amino acid N use efficiency (NUEFAA) for soil microbes, which is a more realistic estimation of soil microbial NUE compared to the NUE estimated by analytical methods. We compare analytical and numerical approaches for two forest soils; suggest improvements of the experimental work for future studies; and conclude that: i) FAA mineralization might be as equally an important rate limiting step for gross N mineralization as peptide depolymerization rate is, because about half of all depolymerized peptide N is consecutively being mineralized; and that ii) FAA mineralization and FAA 20 immobilization rates should be used for assessing NUEFAA.
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| 8. |
- Andresen, Louise C., 1974, et al.
(author)
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Free amino acids in the rhizosphere
- 2014
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In: 19th European Nitrogen Cycle Meeting. September 10-12th 2014, Gent, Belgium.
-
Conference paper (other academic/artistic)
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| 9. |
- Andresen, Louise C., 1974, et al.
(author)
-
Nitrogen dynamics after two years of elevated CO2 in phosphorus limited Eucalyptus woodland
- 2020
-
In: Biogeochemistry. - : Springer Science and Business Media LLC. - 0168-2563 .- 1573-515X. ; 150, s. 297-312
-
Journal article (peer-reviewed)abstract
- It is uncertain how the predicted further rise of atmospheric carbon dioxide (CO2) concentration will affect plant nutrient availability in the future through indirect effects on the gross rates of nitrogen (N) mineralization (production of ammonium) and depolymerization (production of free amino acids) in soil. The response of soil nutrient availability to increasing atmospheric CO2 is particularly important for nutrient poor ecosystems. Within a FACE (Free-Air Carbon dioxide Enrichment) experiment in a native, nutrient poor Eucalyptus woodland (EucFACE) with low soil organic matter (≤ 3%), our results suggested there was no shortage of N. Despite this, microbial N use efficiency was high (c. 90%). The free amino acid (FAA) pool had a fast turnover time (4 h) compared to that of ammonium (NH4+) which was 11 h. Both NH4-N and FAA-N were important N pools; however, protein depolymerization rate was three times faster than gross N mineralization rates, indicating that organic N is directly important in the internal ecosystem N cycle. Hence, the depolymerization was the major provider of plant available N, while the gross N mineralization rate was the constraining factor for inorganic N. After two years of elevated CO2, no major effects on the pools and rates of the soil N cycle were found in spring (November) or at the end of summer (March). The limited response of N pools or N transformation rates to elevated CO2 suggest that N availability was not the limiting factor behind the lack of plant growth response to elevated CO2, previously observed at the site.
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| 10. |
- Andresen, Louise C., 1974, et al.
(author)
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Patterns of free amino acids in tundra soils reflect mycorrhizal type, shrubification, and warming
- 2022
-
In: Mycorrhiza. - : Springer Science and Business Media LLC. - 0940-6360 .- 1432-1890. ; 32:3-4, s. 305-313
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Journal article (peer-reviewed)abstract
- The soil nitrogen (N) cycle in cold terrestrial ecosystems is slow and organically bound N is an important source of N for plants in these ecosystems. Many plant species can take up free amino acids from these infertile soils, either directly or indirectly via their mycorrhizal fungi. We hypothesized that plant community changes and local plant community differences will alter the soil free amino acid pool and composition; and that long-term warming could enhance this effect. To test this, we studied the composition of extractable free amino acids at five separate heath, meadow, and bog locations in subarctic and alpine Scandinavia, with long-term (13 to 24 years) warming manipulations. The plant communities all included a mixture of ecto-, ericoid-, and arbuscular mycorrhizal plant species. Vegetation dominated by grasses and forbs with arbuscular and non-mycorrhizal associations showed highest soil free amino acid content, distinguishing them from the sites dominated by shrubs with ecto- and ericoid-mycorrhizal associations. Warming increased shrub and decreased moss cover at two sites, and by using redundancy analysis, we found that altered soil free amino acid composition was related to this plant cover change. From this, we conclude that the mycorrhizal type is important in controlling soil N cycling and that expansion of shrubs with ectomycorrhiza (and to some extent ericoid mycorrhiza) can help retain N within the ecosystems by tightening the N cycle.
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| 11. |
- Andresen, Louise C., 1974, et al.
(author)
-
Simultaneous quantification of depolymerization and mineralization rates by a novel 15N tracing model
- 2016
-
In: SOIL. - : Copernicus GmbH. - 2199-398X. ; 2, s. 433-442
-
Journal article (peer-reviewed)abstract
- The depolymerization of soil organic matter, such as proteins and (oligo-)peptides, into monomers (e.g. amino acids) is currently considered to be the rate-limiting step for nitrogen (N) availability in terrestrial ecosystems. The mineralization of free amino acids (FAAs), liberated by the depolymerization of peptides, is an important fraction of the total mineralization of organic N. Hence, the accurate assessment of peptide depoly- merization and FAA mineralization rates is important in order to gain a better process-based understanding of the soil N cycle. In this paper, we present an extended numerical 15 N tracing model Ntrace , which incorporates the FAA pool and related N processes in order to provide a more robust and simultaneous quantification of de- polymerization and gross mineralization rates of FAAs and soil organic N. We discuss analytical and numerical approaches for two forest soils, suggest improvements of the experimental work for future studies, and conclude that (i) when about half of all depolymerized peptide N is directly mineralized, FAA mineralization can be as important a rate-limiting step for total gross N mineralization as peptide depolymerization rate; (ii) gross FAA mineralization and FAA immobilization rates can be used to develop FAA use efficiency (NUEFAA), which can reveal microbial N or carbon (C) limitation.
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| 12. |
- Aurangojeb, Mohammad, et al.
(author)
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Nitrous oxide emissions from Norway spruce forests on drained organic and mineral soil
- 2017
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In: Canadian Journal of Forest Research. - : Canadian Science Publishing. - 0045-5067 .- 1208-6037. ; 47:11, s. 1482-1487
-
Journal article (peer-reviewed)abstract
- Nitrous oxide (N2O) emissions from drained organic (Histosol) and mineral (Umbrisol) soils having a 60 year old Norway spruce (Picea abies (L.) Karst.) forest in a catchment in southwest Sweden were measured using static closed chambers every other week over 3 years (August 2010 - July 2013). High emissions were observed during the summer months for both sites, which were significantly higher for the drained organic soils compared to the mineral soils: average emissions of 49.0 +/- 3.3 and 8.0 +/- 3.3 mu g N2O.m(-2).h(-1), respectively. As the experiment was designed to have similar forest and weather conditions for both sites, these were omitted as explanatory factors for the emission difference. Initially, the soil organic matter concentration (percent by mass) difference was thought to be the cause. However, the results found that the soil organic matter amount per square metre of top soil was similar at both sites, suggesting other possible explanations. We propose that the most plausible explanation is that higher tree growth and mycorrhizal nitrogen demand reduce nitrogen availability contributing to the lower N2O emissions from the mineral soil site.
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| 13. |
- Bauters, Marijn, et al.
(author)
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Contrasting nitrogen fluxes in African tropical forests of the Congo Basin
- 2019
-
In: Ecological Monographs. - : Wiley. - 0012-9615 .- 1557-7015. ; 89:1
-
Journal article (peer-reviewed)abstract
- The observation of high losses of bioavailable nitrogen (N) and N richness in tropical forests is paradoxical with an apparent lack of N input. Hence, the current concept asserts that biological nitrogen fixation (BNF) must be a major N input for tropical forests. However, well-characterized N cycles are rare and geographically biased; organic N compounds are often neglected and soil gross N cycling is not well quantified. We conducted comprehensive N input and output measurements in four tropical forest types of the Congo Basin with contrasting biotic (mycorrhizal association) and abiotic (lowland–highland) environments. In 12 standardized setups, we monitored N deposition, throughfall, litterfall, leaching, and export during one hydrological year and completed this empirical N budget with nitrous oxide (N2O) flux measurement campaigns in both wet and dry season and insitu gross soil N transformations using 15N-tracing and numerical modeling. We found that all forests showed a very tight soil N cycle, with gross mineralization to immobilization ratios (M/I) close to 1 and relatively low gross nitrification to mineralization ratios (N/M). This was in line with the observation of dissolved organic nitrogen (DON) dominating N losses for the most abundant, arbuscular mycorrhizal associated, lowland forest type, but in contrast with high losses of dissolved inorganic nitrogen (DIN) in all other forest types. Altogether, our observations show that different forest types in central Africa exhibit N fluxes of contrasting magnitudes and N-species composition. In contrast to many Neotropical forests, our estimated N budgets of central African forests are imbalanced by a higher N input than output, with organic N contributing significantly to the input-output balance. This suggests that important other losses that are unaccounted for (e.g., NOx and N2 as well as particulate N) might play a major role in the N cycle of mature African tropical forests.
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| 14. |
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| 15. |
- Björsne, Anna-Karin, 1983, et al.
(author)
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Combined climate factors alleviate changes in gross soil nitrogen dynamics in heathlands
- 2014
-
In: Biogeochemistry. - : Springer Science and Business Media LLC. - 0168-2563 .- 1573-515X. ; 120:1-3, s. 191-201
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Journal article (peer-reviewed)abstract
- The ongoing climate change affects biogeochemical cycling in terrestrial ecosystems, but the magnitude and direction of this impact is yet unclear. To shed further light on the climate change impact, we investigated alterations in the soil nitrogen (N) cycling in a Danish heathland after 5 years of exposure to three climate change factors, i.e. warming, elevated CO2 (eCO(2)) and summer drought, applied both in isolation and in combination. By conducting laboratory N-15 tracing experiments we show that warming increased both gross N mineralization and nitrification rates. In contrast, gross nitrification was decreased by eCO(2), an effect that was more pronounced when eCO(2) was combined with warming and drought. Moreover, there was an interactive effect between the warming and CO2 treatment, especially for N mineralization: rates increased at warming alone but decreased at warming combined with eCO(2). In the full treatment combination, simulating the predicted climate for the year 2075, gross N transformations were only moderately affected compared to control, suggesting a minor alteration of the N cycle due to climate change. Overall, our study confirms the importance of multifactorial field experiments for a better understanding of N cycling in a changing climate, which is a prerequisite for more reliable model predictions of ecosystems responses to climate change.
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| 16. |
- Björsne, Anna-Karin, 1983, et al.
(author)
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Effect of climate change on soil nitrogen dynamics in a heathland
- 2012
-
In: BIOGEOMON 2012, Northport, Maine, USA, 2012-07-16.
-
Conference paper (other academic/artistic)abstract
- Climate change is likely to affect all levels of the global biosphere. Nitrogen (N) is limiting for net primary production (NPP) in most terrestrial ecosystems and therefore a crucial factor for the ecosystem response to climate change. The hypothesis of progressive nitrogen limitation (PNL) predicts that if NPP is stimulated by elevated CO2 (eCO2), N will become limiting in the ecosystems over time, since the plants will sequester more N with increased carbon uptake (Luo et al. 2004). However, PNL tells nothing of the response of soil N cycling to eCO2. If turnover rates of N accelerate together with decreasing N losses it would lead to increased soil N availability, which would alleviate PNL (Rütting et al. 2010). The N cycle response to a changing climate is however still poorly understood. Only a few studies have investigated how ecosystems are affected by exposure to multiple climate factors and if responses are variable over time. This study is part of CLIMAITE (Climate change effects on biological processes in terrestrial ecosystems), simulating the projected climate conditions for Denmark in 2075 (Mikkelsen et al. 2008). We have investigated how the gross mineralization rates in a heathland are affected by climate change after 2 and 5 years of manipulation. The study site was exposed to three climate factors; eCO2, increased temperature and prolonged summer drought, both single and in combination, in a total of eight different treatments. We have measured the gross mineralization rates with stable isotope techniques in 2010 and compared with mineralization data from 2007. The aim of the study is to understand how climate change affects soil mineralization and if responses on soil nitrogen turnover vary over time of exposure to climate change. Results will be discussed in the light of changes in physico-chemical soil properties as well as compared to other studies.
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| 17. |
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| 18. |
- Bonaglia, Stefano, 1983, et al.
(author)
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High methane emissions from an anoxic fjord driven by mixing and oxygenation : High methane emissions from fjords
- 2022
-
In: Limnology and Oceanography Letters. - : Wiley. - 2378-2242. ; 7:5, s. 392-400
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Journal article (peer-reviewed)abstract
- Oceanic methane (CH4) budgets lack data from high-latitude fjords that often behave as intermittently anoxic ecosystems with potentially high methane emissions. We conducted 15 expeditions and 49 in situ lander deployments in an anoxic Scandinavian fjord between 2009 and 2021. Benthic fluxes were highest at the deepest anoxic site (average 516μmol CH4 m−2 d−1), supporting bottom water methane exceeding 5000nM. Natural and engineered mixing events displaced methane-rich bottom waters, enhancing upper water concentrations and driving high sea–air flux reaching 641μmol CH4 m−2 d−1. Mixing also reduced pelagic methane oxidation from 70% to 20% of all methane sources into the fjord. Upscaling of literature fluxes combined with our results suggests that fjords globally emit 1.0±0.8 Tg CH4 yr−1. Despite their small global area, fjords are hotspots of methane release. We suggest that ongoing deoxygenation and global change will enhance methane emissions from fjords.
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| 19. |
- Braun, Judith, et al.
(author)
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Full15N tracer accounting to revisit major assumptions of 15N isotope pool dilution approaches for gross nitrogen mineralization
- 2018
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In: Soil Biology and Biochemistry. - : Elsevier BV. - 0038-0717. ; 117, s. 16-26
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Journal article (peer-reviewed)abstract
- © 2017 The Authors The 15 N isotope pool dilution (IPD) technique is the only available method for measuring gross ammonium (NH 4 + ) production and consumption rates. Rapid consumption of the added 15 N-NH 4 + tracer is commonly observed, but the processes responsible for this consumption are not well understood. The primary objectives of this study were to determine the relative roles of biotic and abiotic processes in 15 N-NH 4 + consumption and to investigate the validity of one of the main assumptions of IPD experiments, i.e., that no reflux of the consumed 15 N tracer occurs during the course of the experiments. We added a 15 N-NH 4 + tracer to live and sterile (autoclaved) soil using mineral topsoil from a beech forest and a grassland in Austria that differed in NH 4 + concentrations and NH 4 + consumption kinetics. We quantified both biotic tracer consumption (i.e. changes in the concentrations and 15 N enrichments of NH 4 + , dissolved organic N (DON), NO 3 − and the microbial N pool) and abiotic tracer consumption (i.e., fixation by clay and/or humic substances). We achieved full recovery of the 15 N tracer in both soils over the course of the 48 h incubation. For the forest soil, we found no rapid consumption of the 15 N tracer, and the majority of tracer (78%) remained unconsumed at the end of the incubation period. In contrast, the grassland soil showed rapid 15 N-NH 4 + consumption immediately after tracer addition, which was largely due to both abiotic fixation (24%) and biotic processes, largely uptake by soil microbes (10%) and nitrification (13%). We found no evidence for reflux of 15 N-NH 4 + over the 48 h incubation period in either soil. Our study therefore shows that 15 N tracer reflux during IPD experiments is negligible for incubation times of up to 48 h, even when rapid NH 4 + consumption occurs. Such experiments are thus robust to the assumption that immobilized labeled N is not re–mobilized during the experimental period and does not impact calculations of gross N mineralization.
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| 20. |
- Chen, Z, et al.
(author)
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Importance of heterotrophic nitrification and dissimilatory nitrate reduction to ammonium in a cropland soil: Evidences from a 15N tracing study to literature synthesis
- 2015
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In: Soil Biology and Biochemistry. - : Elsevier BV. - 0038-0717 .- 1879-3428. ; 91, s. 65-75
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Journal article (peer-reviewed)abstract
- Future climate change is predicted to influence soil moisture regime, a key factor regulating soil nitrogen (N) cycling. To elucidate how soil moisture affects gross N transformation in a cultivated black soil, a 15N tracing study was conducted at 30%, 50% and 70% water-filled pore space (WFPS). While gross mineralization rate of recalcitrant organic N (Nrec) increased from 0.56 to 2.47 mg N kg−1 d−1, the rate of labile organic N mineralization declined from 4.23 to 2.41 mg N kg−1 d−1 with a WFPS increase from 30% to 70%. Similar to total mineralization, no distinct moisture effect was found on total immobilization of ammonium, which primarily entered the Nrec pool. Nitrate (NO3−) was mainly produced via autotrophic nitrification, which was significantly stimulated by increasing WFPS. Unexpectedly, heterotrophic nitrification was observed, with the highest rate of 1.06 mg N kg−1 d−1 at 30% WFPS, contributing 31.8% to total NO3− production, and decreased with WFPS. Dissimilatory nitrate reduction to ammonium (DNRA) increased from near zero (30% WFPS) to 0.26 mg N kg−1 d−1 (70% WFPS), amounting to 16.7–92.9% of NO3− consumption. A literature synthetic analysis from global multiple ecosystems showed that the rates of heterotrophic nitrification and DNRA in test soil were comparative to the forest and grassland ecosystems, and that heterotrophic nitrification was positively correlated with precipitation, soil organic carbon (SOC) and C/N, but negatively with pH and bulk density, while DNRA showed positive relationships with precipitation, clay, SOC, C/NO3− and WFPS. We suggested that low pH and bulk density and high SOC and C/N in test soil might favor heterotrophic nitrification, and that C and NO3− availability together with anaerobic condition were crucial for DNRA. Overall, our study highlights the role of moisture in regulating gross N turnover and the importance of heterotrophic nitrification for NO3− production under low moisture and DNRA for NO3− retention under high moisture in cropland.
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| 21. |
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| 22. |
- Daebeler, A., et al.
(author)
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Soil warming and fertilization altered rates of nitrogen transformation processes and selected for adapted ammonia-oxidizing archaea in sub-arctic grassland soil
- 2017
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In: Soil Biology & Biochemistry. - : Elsevier BV. - 0038-0717. ; 107, s. 114-124
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Journal article (peer-reviewed)abstract
- The balance of microbial nitrogen (N) transformation processes in sub-arctic terrestrial ecosystems is most likely affected by global change, with potential feedbacks to greenhouse gas emissions and eutrophication. Soil temperature and N availability their global increases being two of the most pressing global change features- will be prime drivers of N dynamics and microbial community structure, but little is known about their interactive effects in these ecosystems. We utilized geothermally warmed soils from Iceland as a natural experiment for assessing fertilization and warming effects on gross soil N transformation processes. Experimental incubations of these soils at different temperatures coupled with a dual N-15-labelling/-tracing approach and pyrotag transcript-sequencing allowed for the analysis of independent and combined impacts of N fertilization and temperature shifts on gross N mineralisation, nitrification, and ammonium and nitrate immobilisation rates and archaeal ammonia oxidizing (AOA) communities, being the key ammonia oxidizers in this soil. Gross nitrification in warmed soil was increased in relation to ambient temperature soil and exhibited a higher temperature optimum. Concomitantly, our results revealed a selection of AOA populations adapted to in situ soil temperatures. Phylogenetically distinct populations of actively ammonia-oxidizing archaea exhibited conserved temperature optima. N mineralization and nitrification showed higher sensitivities in response to short-term temperature changes if the soils had been warmed. In part, the influence of short-term temperature changes could however be neutralized by the effects of N fertilization. Long-term N fertilization alone affected only gross N mineralization. However, all gross N transformation rates were significantly altered by the interactive effects of N fertilization and soil warming. We conclude that in order to reliably predict effects of global change on sub-arctic soil N transformation processes we need to consider multiple interactions among global change factors and to take into account the capacity of soil microbial populations to adapt to global change conditions. (C) 2016 Elsevier Ltd. All rights reserved.
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| 23. |
- Demey, A., et al.
(author)
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Hemiparasitic litter additions alter gross nitrogen turnover in temperate semi-natural grassland soils
- 2014
-
In: Soil Biology & Biochemistry. - : Elsevier BV. - 0038-0717. ; 68, s. 419-428
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Journal article (peer-reviewed)abstract
- Hemiparasitic plants accumulate nutrients in their leaves and therefore produce high-quality litter with faster decomposition and nutrient release rates compared to non-parasitic litter. Higher levels of plant-available nitrogen (N) in the presence of hemiparasitic plants have been attributed to this 'litter effect', but effects on N dynamics in the soil remain unstudied. We tested the hypothesis that litter of Rhinanthus angustifolius and Pedicularis sylvatica increases N transformation rates in the soil more than non-parasitic litter of a species mix from the same communities. We expected the litter effect to be higher in the oligotrophic Pedicularis soil compared to the mesotrophic Rhinanthus soil. Gross N transformation rates were quantified using a N-15 tracing modeling approach. Differentially N-15 labeled NH4Cl + KNO3 was added to two soils with three treatments (control, soil amended with non-parasitic litter, soil amended with Rhinanthus or Pedicularis litter) in a laboratory incubation experiment. The concentration and 15N enrichment of NH4+ and NO3 in the soil were measured at six time points within one or two weeks (depending on the soil) after label addition. Hemiparasitic litter addition increased the overall cycling of N more compared to the addition of non-parasitic litter. Relative to the non-parasitic litter, addition of Rhinanthus litter increased the net flux from organic N to NH4+ by 61% and net (autotrophic) nitrification by 80%. Addition of Pedicularis litter increased the net flux from organic N to NH4+ by 28% relative to addition of non-parasitic litter, while there was no effect on nitrification. Surprisingly, gross mineralization of organic N to NH4+ decreased with litter addition for the Rhinanthus soil (control soil > nonparasitic litter > Rhinanthus litter), while it increased with litter addition in the Pedicularis soil (control soil < non-parasitic litter < Pedicularis litter). Our results support the hypothesis that litter from hemiparasitic plants increases soil N availability more than non-parasitic litter, but contradicts the expectation that the hemiparasitic litter effect would be more pronounced in an oligotrophic as compared to a mesotrophic system. This litter-induced augmentation in soil fertility provides in addition to the parasitic suppression of hosts a second potentially important pathway by which hemiparasitic plants impact on plant community composition. However, future research on P and K return via hemiparasitic litter should be considered. (C) 2013 Elsevier Ltd. All rights reserved.
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| 24. |
- Ernfors, Maria, 1973, et al.
(author)
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Increased nitrous oxide emissions from a drained organic
- 2011
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In: Plant and soil.
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Journal article (peer-reviewed)abstract
- The aim of this study was to determine how roots and their ectomycorrhizal symbionts affect the fluxes of nitrous oxide (N2O) from nutrient-rich drained organic forest soils. Specifically, the relative impacts of roots and mycorrhizal mycelia on N2O fluxes were investigated using two different trenching treatments, excluding (a) roots or (b) roots and mycorrhizal mycelia, from the soil. N2O fluxes were measured at the soil surface, for 1 year before and 2.5 years after trenching, within the two trenching treatments and on untreated controls. While the exclusion of roots alone did not affect N2O emissions, the simultaneous exclusion of roots and mycorrhizal mycelia doubled N2O emissions, compared to the control plots. Two probable explanations for the increased fluxes were identified: (1) a decreased uptake of nitrogen (N) from the soil, through the mycorrhizal fungi, which increased N availability for the N2O-producing microorganisms, and (2) a decreased uptake of water from the soil, through the mycorrhiza, which increased the soil water content and thus the N2O emissions from denitrification. If the trenching reduced any potential stimulation of N cycling, through rhizodeposition, this mechanism did not outweigh the effects of a discontinued mycorrhizal N and/or water uptake on N2O fluxes. The results of the study emphasise the importance of ectomycorrhiza in regulating N2O emissions from forested organic soils.
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| 25. |
- Ernfors, Maria, 1973, et al.
(author)
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Increased nitrous oxide emissions from a drained organic forest soil after exclusion of ectomycorrhizal mycelia
- 2011
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In: Plant and Soil. - 0032-079X. ; 343:1-2, s. 161-170
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Journal article (peer-reviewed)abstract
- The aim of this study was to determine how roots and their ectomycorrhizal symbionts affect the fluxes of nitrous oxide (N2O) from nutrient-rich drained organic forest soils. Specifically, the relative impacts of roots and mycorrhizal mycelia on N2O fluxes were investigated using two different trenching treatments, excluding (a) roots or (b) roots and mycorrhizal mycelia, from the soil. N2O fluxes were measured at the soil surface, for 1 year before and 2.5 years after trenching, within the two trenching treatments and on untreated controls. While the exclusion of roots alone did not affect N2O emissions, the simultaneous exclusion of roots and mycorrhizal mycelia doubled N2O emissions, compared to the control plots. Two probable explanations for the increased fluxes were identified: (1) a decreased uptake of nitrogen (N) from the soil, through the mycorrhizal fungi, which increased N availability for the N2O-producing microorganisms, and (2) a decreased uptake of water from the soil, through the mycorrhiza, which increased the soil water content and thus the N2O emissions from denitrification. If the trenching reduced any potential stimulation of N cycling, through rhizodeposition, this mechanism did not outweigh the effects of a discontinued mycorrhizal N and/or water uptake on N2O fluxes. The results of the study emphasise the importance of ectomycorrhiza in regulating N2O emissions from forested organic soils.
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