| 1. |
- Kehoe, Laura, et al.
(författare)
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Make EU trade with Brazil sustainable
- 2019
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Ingår i: Science. - : American Association for the Advancement of Science (AAAS). - 0036-8075 .- 1095-9203. ; 364:6438, s. 341-
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)
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| 2. |
- Andresen, Louise C., 1974, et al.
(författare)
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Depolymerization and mineralization – investigating N availability by a novel 15N tracing model
- 2016
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Ingår i: SOIL. - : Copernicus GmbH. - 2199-398X. ; 2:3, s. 433-442
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)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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| 3. |
- Andresen, Louise C., 1974, et al.
(författare)
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Simultaneous quantification of depolymerization and mineralization rates by a novel 15N tracing model
- 2016
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Ingår i: SOIL. - : Copernicus GmbH. - 2199-398X. ; 2, s. 433-442
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Tidskriftsartikel (refereegranskat)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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| 4. |
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| 5. |
- Björsne, Anna-Karin, 1983, et al.
(författare)
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Combined climate factors alleviate changes in gross soil nitrogen dynamics in heathlands
- 2014
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Ingår i: Biogeochemistry. - : Springer Science and Business Media LLC. - 0168-2563 .- 1573-515X. ; 120:1-3, s. 191-201
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Tidskriftsartikel (refereegranskat)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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| 6. |
- Björsne, Anna-Karin, 1983, et al.
(författare)
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Effect of climate change on soil nitrogen dynamics in a heathland
- 2012
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Ingår i: BIOGEOMON 2012, Northport, Maine, USA, 2012-07-16.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)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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| 7. |
- Björsne, Anna-Karin, 1983
(författare)
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The Nitrogen Cycle in Soil - Climate Impact and Methodological Challenges in Natural Ecosystems
- 2018
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Nitrogen (N) is a fundamental element for life, and limiting in many terrestrial ecosystems. In non-N-fertilized ecosystems, the N inputs can be low, and the nutrient availability for plants is determined by the internal cycling of N. The N availability might alter with different factors, such as climate change, forest management practices, and tree species. Soil N cycling is investigated using stable isotopes, where the activity in the soil can be monitored over time. The overall aim of this thesis is to increase the understanding of the N cycle in natural and semi-natural ecosystems and the environmental factors important for nutrient cycling. The results show that all sites investigated in this thesis had higher NH4+ turnover than NO3- turnover. The mineralization rates were highest in the site with the lowest C:N ratio, and the lowest mineralization rates and the highest C:N ratio in the spruce forests, which demonstrate the importance of organic matter quality on gross N transformation rates. The N cycle responses to combined climate treatments were generally lower than responses to single climate treatments. For some processes, we observed opposing responses for eCO2 as single and main treatment compared to the plots receiving the full treatment. This point to the importance of conducting multifactor climate change experiments, as many feedback controls are yet unknown. Gross nitrification was lowered with fertilization in a northern boreal forest, which is an interesting result in the light of the very low nitrous oxide (N2O) emissions from the investigated site, despite heavy annual fertilization of 50–70 kg ha-1. Moreover, the results from an experiment with soil of common origin and land history showed generally higher gross mineralization, immobilization and nitrification rates a beech stand compared to a spruce stand. The beech stand had also higher initial concentration of nitrate (NO3-) which indicates a more NO3- based N cycling. Finally, numerical modeling together with 15N tracing is an improvement for simultaneously determining free amino acid (FAA) mineralization, peptide depolymerization and gross N mineralization rates, compared to analytical solutions. This thesis confirms that N cycling in natural ecosystems is governed by the properties of the soil, vegetation and climate, but also that the experimental set-up strongly affects the outcome of the experiment. In turn, this affects the potential of doing reliable experiments, especially in ecosystems where the external inputs of N are very low. The thesis also highlights some methodological challenges that lie in the future of N cycling research.
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| 8. |
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| 9. |
- Rütting, Tobias, 1977, et al.
(författare)
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Low Nitrous Oxide Emissions in a Boreal Spruce Forest Soil, Despite Long-Term Fertilization
- 2021
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Ingår i: Frontiers in Forests and Global Change. - : Frontiers Media SA. - 2624-893X. ; 4
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Tidskriftsartikel (refereegranskat)abstract
- Nitrogen (N) fertilization can increase stem wood production by several hundred percent in boreal forests. At the same time, there are concerns about the environmental consequences of N fertilization, especially considering losses of the greenhouse gas nitrous oxide (N2O) to the atmosphere. Soils are a large contributor to N2O emissions on a global scale. The aim of this study was to investigate the consequences of long-term nutrient optimization fertilization on N2O emissions in a boreal forest in Northern Sweden. Field N2O flux measurements were conducted during 2 years with manual and automatic chambers, as well as gas probes in the snow. The N2O emissions were generally low during the whole period of measurements, both from the control and fertilized plots. The emissions were generally highest during the winters, as well as the variability in the observed values. Overall, N2O emissions from fertilized plots were about twice the control, which could be explained by changes in the soil carbon-to-nitrogen ratio.
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