| 1. |
- Drouin-Ouellet, Janelle, et al.
(författare)
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Age-related pathological impairments in directly reprogrammed dopaminergic neurons derived from patients with idiopathic Parkinson's disease
- 2022
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Ingår i: Stem Cell Reports. - : Elsevier BV. - 2213-6711. ; 17:10, s. 2203-2219
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Tidskriftsartikel (refereegranskat)abstract
- We have developed an efficient approach to generate functional induced dopaminergic (DA) neurons from adult human dermal fibroblasts. When performing DA neuronal conversion of patient fibroblasts with idiopathic Parkinson's disease (PD), we could specifically detect disease-relevant pathology in these cells. We show that the patient-derived neurons maintain age-related properties of the donor and exhibit lower basal chaperone-mediated autophagy compared with healthy donors. Furthermore, stress-induced autophagy resulted in an age-dependent accumulation of macroautophagic structures. Finally, we show that these impairments in patient-derived DA neurons leads to an accumulation of phosphorylated alpha-synuclein, the classical hallmark of PD pathology. This pathological phenotype is absent in neurons generated from induced pluripotent stem cells from the same patients. Taken together, our results show that direct neural reprogramming can be used for obtaining patient-derived DA neurons, which uniquely function as a cellular model to study age-related pathology relevant to idiopathic PD.
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| 2. |
- Falk, Julie Maria, et al.
(författare)
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Effects of simulated increased grazing on carbon allocation patterns in a high arctic mire
- 2014
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Ingår i: Biogeochemistry. - : Springer Science and Business Media LLC. - 1573-515X .- 0168-2563. ; 119:1-3, s. 229-244
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Tidskriftsartikel (refereegranskat)abstract
- Herbivory is an important part of most ecosystems, and grazing alone can have a considerable impact on the ecosystems carbon balance with both direct and indirect effects. Removal of above-ground biomass by consumption of herbivores will change the below-ground carbon stock; the reduction of litter that goes into the ground will influence the total ecosystem carbon content. Little is however known about how plant-herbivory interactions effect the carbon balance, in particular methane emissions, of high arctic mires. We hypothesized that increased grazing pressure will change carbon allocation patterns resulting in decreased net ecosystem uptake of carbon and subsequently in lower methane emissions. An in-situ field experiment was conducted over 3 years in a high arctic mire at Zackenberg in NE Greenland. The experiment consisted of three treatments, with five replicates of each (1) control, (2) vascular plants were removed (NV), (3) clipped twice each growing season in order to simulate increased muskox grazing. Immediately after the initiation of the experiment net ecosystem uptake of CO2 decreased in clipped plots (mean total decrease for the three following years was 35 %). One year into the experiment a significantly lower CH4 emission was observed in these plots, the total mean reduction for the following 2 years was 26 %. Three years into the experiment significantly lower substrate (acetic acid) availability for CH4 production was observed (27 % reduction). NV plots had a mean decrease in CO2 uptake of 113 %, a 62 % decrease in ecosystem respiration and an 84 % decrease in CH4 emission (mean of all 3 years). Our study shows that increased grazing pressure in a high arctic mire can lead to significant changes in the carbon balance, with lower CO2 uptake leading to lower production of substrate for CH4 formation and in lower CH4 emission.
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| 3. |
- Falk, Julie Maria, et al.
(författare)
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Large herbivore grazing affects the vegetation structure and greenhouse gas balance in a high arctic mire
- 2015
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Ingår i: Environmental Research Letters. - : IOP Publishing. - 1748-9326. ; 10:4
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Tidskriftsartikel (refereegranskat)abstract
- Herbivory is an important part of most ecosystems and affects the ecosystems' carbon balance both directly and indirectly. Little is known about herbivory and its impact on the carbon balance in high arctic mire ecosystems. We hypothesized that trampling and grazing by large herbivores influences the vegetation density and composition and thereby also the carbon balance. In 2010, we established fenced exclosures in high arctic Greenland to prevent muskoxen (Ovibos moschatus) from grazing. During the growing seasons of 2011 to 2013 we measured CO2 and CH4 fluxes in these ungrazed blocks and compared them to blocks subjected to natural grazing. Additionally, we measured depth of the water table and active layer, soil temperature, and in 2011 and 2013 an inventory of the vegetation density and composition were made. In 2013 a significant decrease in total number of vascular plant (33-44%) and Eriophorum scheuchzeri (51-53%) tillers were found in ungrazed plots, the moss-layer and amount of litter had also increased substantially in these plots. This resulted in a significant decrease in net ecosystem uptake of CO2 (47%) and likewise a decrease in CH4 emission (44%) in ungrazed plots in 2013. While the future of the muskoxen in a changing arctic is unknown, this experiment points to a potentially large effect of large herbivores on the carbon balance in natural Arctic ecosystems. It thus sheds light on the importance of grazing mammals, and hence adds to our understanding of natural ecosystem greenhouse gas balance in the past and in the future.
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| 4. |
- Falk, Julie Maria
(författare)
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Plant-soil-herbivore interactions in a high Arctic wetland - Feedbacks to the carbon cycle
- 2014
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Arctic ecosystems hold massive amounts of the global carbon in their soils and are of great importance for the global terrestrial exchange of greenhouse gases to the atmosphere. The arctic region has in general been acting as a C sink for the past 10000 years, however with climate change the C balance in some areas is shifting towards becoming a C source. Herbivory are an important part of many ecosystems and have been found to have an important impact on the C balance. This seemingly important aspect of the C balance in arctic ecosystems are however very rarely considered. In this project, the interactions between plants, soil and herbivores have been studied in a high arctic mire in Zackenberg, northeast Greenland. The aim of the project was to study the impact of the large herbivores muskoxen on the vegetation composition and density, CO2 and CH4 fluxes and substrate availably for CH4 production. Over a time period of three years three in-situ field studies were conducted. In paper one and two of this thesis treatments were applied that simulate plausible responses of the muskoxen population with climate change. In paper I muskoxen was excluded from part of the Zackenberg mire, thus representing a decrease in the population. In paper II the grazing pressure was increased, by clipping of plots twice each summer. In paper IV the main in-situ drivers of the spatial variability of CH4 flux was studied. Further, a laboratory study (paper III) was conducted to make an in-depth study on the C allocation pattern in the area and the consequences of clipping. To our surprise, the results from paper I and II showed that the ecosystem responded in similar ways to changes in grazing pressure despite the contrasting treatments. Both increased and decreased grazing resulted in a decrease in the density of vascular plants, in particular of Eriophorum scheuchzeri (Erioph), and in a substantial decrease in CO2 and CH4 fluxes. The third year into the exclusion experiment in paper I the mean Net Ecosystem Exchange (NEE) of CO2 had decrease with 47%, while the CH4 emission had decreased with 44%. In the clipping experiment in paper II NEE decreased already in year one of the experiment and had after three years decreased with on average 35%. A change in CH4 emission was apparent in year two and over the last two years CH4 emission decreased with on average 26%. In the laboratory study, several factors indicated that clipping altered the C allocation pattern and resulted in more C allocation to above ground vegetation and more root exudation. The results from paper IV showed that there is a strong dependence of the spatial variability in CH4 flux on productivity and C input to vegetation and pore water. The main driver of this carbon input is the vegetation composition, with high number of Erioph tillers leading to high input. Consequently, since both decreased and increased grazing pressure resulted in a decrease in Erioph density both these treatments ultimately resulted in lower productivity and decreased CH4 fluxes. In conclusion, the results from this thesis clearly show that herbivores are of great importance for the C balance of this wet arctic ecosystem, the driving forces behind this effect being interactions between plants, soil and herbivores. The results from this thesis further points to the importance of considering the impact of herbivory when the past, present or future C balance in the arctic is discussed.
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| 5. |
- Lund, Magnus, et al.
(författare)
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Trends in CO2 exchange in a high Arctic tundra heath, 2000-2010
- 2012
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Ingår i: Journal of Geophysical Research. - 2156-2202. ; 117
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Tidskriftsartikel (refereegranskat)abstract
- We have measured the land-atmosphere CO2 exchange using the eddy covariance technique in a high Arctic tundra heath in northeast Greenland (Zackenberg). On the basis of 11 years of measurements (2000-2010), it was found that snow cover dynamics was important for the CO2 exchange. The start of CO2 uptake period correlated significantly with timing of snowmelt. Furthermore, for years with deep and long-lasting snowpacks, the following springs showed increased CO2 emission rates. In the first part of the study period, there was an increase of approximately 8 g C m(-2) yr(-1) in both accumulated gross primary production (GPP) and CO2 sink strength during summer. However, in the last few years, there were no significant changes in GPP, whereas ecosystem respiration (R-eco) increased (8.5 g C m(-2) yr(-1)) and ecosystem CO2 sink strength weakened (-4.1 g C m(-2) yr(-1)). It was found that temperature and temperature-related variables (maximum thaw depth and growing degree days) controlled the interannual variation in CO2 exchange. However, while R-eco showed a steady increase with temperature (5.8 g C m(-2) degrees C-1), the initial increase in GPP with temperature leveled off at the high end of observed temperature range. This suggests that future increases in temperature will weaken the ecosystem CO2 sink strength or even turn it into a CO2 source, depending on possible changes in vegetation structure and functioning as a response to a changing climate. If this trend is applicable also to other Arctic ecosystems, it will have implications for our current understanding of Arctic ecosystems dynamics.
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| 6. |
- Riget, Frank, et al.
(författare)
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Mercury (Hg) Transport in a High Arctic River in Northeast Greenland
- 2011
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Ingår i: Water, Air and Soil Pollution. - : Springer Science and Business Media LLC. - 1573-2932 .- 0049-6979. ; 222:1-4, s. 233-242
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Tidskriftsartikel (refereegranskat)abstract
- In a warming climate, mercury (Hg) pathways in the Arctic can be expected to be affected. The Hg transport from the high arctic Zackenberg River Basin was assessed in 2009 in order to describe and estimate the mercury transported from land to the marine environment. A total of 95 water samples were acquired and filtered (0.4 mu m pore size), and Hg concentrations were determined in both the filtered water and in the sediment. A range of other elements were also measured in the water samples. Hg concentrations in the filtered water were in general highest in the beginning of the season when the water came mainly from melted snow. THg concentrations in the sediment were in general relatively constant or slightly decreasing until mid-August, where after the concentrations increased. A principal component analysis separated the samples into spring, summer and autumn samples indicating seasonal characteristics of the patterns of element concentrations. The total amount of Hg in the sediment transported was estimated to 2.6 kg. Approximately 60% of the sediment-transported Hg occurred during a 24-h flood in the beginning of August caused by a glacial lake outburst flood. The total amount of transported dissolved Hg was estimated to 46 g, and 13% of this transport occurred during the 24-h flood. If it is assumed that the Hg transport by Zackenberg River is representative for the general glacial rivers in East Greenland, the total Hg transport into the North Atlantic from Greenland alone is approximately 4.6 tons year(-1) with an estimated annual freshwater discharge of similar to 440 km(3).
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| 7. |
- Ström, Lena, et al.
(författare)
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Controls of spatial and temporal variability in CH4 flux in a high arctic fen over three years
- 2015
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Ingår i: Biogeochemistry. - : Springer Science and Business Media LLC. - 1573-515X .- 0168-2563. ; 125:1, s. 21-35
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Tidskriftsartikel (refereegranskat)abstract
- The aim of this study was to establish the main drivers of the spatial variability in growing season CH4 flux within an arctic wetland ecosystem. During 3 years (2011-2013) we measured CH4 flux and potential drivers, e.g., CO2 fluxes (net ecosystem exchange (NEE), gross primary productivity (GPP) and ecosystem respiration), temperature, water table depth, pore-water concentration of organic acids (e.g., acetate) and the vascular plant composition and density. The study included 16-20 main plots (C-main) and in 2013 also experimental plots (10 excluded muskoxen grazing, 9 snow fence and 10 automated chamber plots) distributed over 0.3 km(2). The results show a 1.8-times difference in CH4 flux magnitude inter-annually and 9- to 35-times spatially (depending on year and treatment). During all 3 years GPP was a strong driver of the variability in C-main plots. Accordingly, the plant productivity related variables NEE, GPP and acetate were singled out as the strongest drivers of the variability in 2013, when all variables were measured on a majority of the plots. These variables were equally strong drivers of the spatial variability in CH4 flux regardless of whether experimental plots were included in the analysis or not. The density of Eriophorum scheuchzeri was the strongest driver of the spatial variability in NEE, GPP and acetate. In conclusion, changes in vegetation composition or productivity of wet arctic ecosystems will have large impacts on their carbon balance and CH4 flux, irrespective of whether these changes are driven directly by climate change or by biotic interactions, such as grazing.
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| 8. |
- Tagesson, Torbern, et al.
(författare)
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Land-atmosphere exchange of methane from soil thawing to soil freezing in a high-Arctic wet tundra ecosystem
- 2012
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Ingår i: Global Change Biology. - : Wiley. - 1354-1013. ; 18:6, s. 1928-1940
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Tidskriftsartikel (refereegranskat)abstract
- The land-atmosphere exchange of methane (CH4) and carbon dioxide (CO2) in a high-Arctic wet tundra ecosystem (Rylek ae rene) in Zackenberg, north-eastern Greenland, was studied over the full growing season and until early winter in 2008 and from before snow melt until early winter in 2009. The eddy covariance technique was used to estimate CO2 fluxes and a combination of the gradient and eddy covariance methods was used to estimate CH4 fluxes. Small CH4 bursts were observed during spring thawing 2009, but these existed during short periods and would not have any significant effect on the annual budget. Growing season CH4 fluxes were well correlated with soil temperature, gross primary production, and active layer thickness. The CH4 fluxes remained low during the entire autumn, and until early winter. No increase in CH4 fluxes were seen as the soil started to freeze. However, in autumn 2008 there were two CH4 burst events that were highly correlated with atmospheric turbulence. They were likely associated with the release of stored CH4 from soil and vegetation cavities. Over the measurement period, 7.6 and 6.5g C m(-2) was emitted as CH4 in 2008 and in 2009, respectively. Rylek ae rene acted as a C source during the warmer and wetter measurement period 2008, whereas it was a C sink for the colder and drier period of 2009. Wet tundra ecosystems, such as Rylek ae rene may thus play a more significant role for the climate in the future, as temperature and precipitation are predicted to increase in the high-Arctic.
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| 9. |
- Tagesson, Torbern, et al.
(författare)
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Modelling of growing season methane fluxes in a high-Arctic wet tundra ecosystem 1997-2010 using in situ and high-resolution satellite data
- 2013
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Ingår i: Tellus. Series B: Chemical and Physical Meteorology. - : Stockholm University Press. - 0280-6509 .- 1600-0889. ; 65
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Tidskriftsartikel (refereegranskat)abstract
- Methane (CH4) fluxes 1997-2010 were studied by combining remotely sensed normalised difference water index (NDWI) with in situ CH4 fluxes from Rylekaerene, a high-Arctic wet tundra ecosystem in the Zackenberg valley, north-eastern Greenland. In situ CH4 fluxes were measured using the closed-chamber technique. Regression models between in situ CH4 fluxes and environmental variables [soil temperature (T-soil), water table depth (WtD) and active layer (AL) thickness] were established for different temporal and spatial scales. The relationship between in situ WtD and remotely sensed NDWI was also studied. The regression models were combined and evaluated against in situ CH4 fluxes. The models including NDWI as the input data performed on average slightly better [root mean square error (RMSE) = 1.56] than the models without NDWI (RMSE = 1.67), and they were better in reproducing CH4 flux variability. The CH4 flux model that performed the best included exponential relationships against temporal variation in T-soil and AL, an exponential relationship against spatial variation in WtD and a linear relationship between WtD and remotely sensed NDWI (RMSE = 1.50). There were no trends in modelled CH4 flux budgets between 1997 and 2010. Hence, during this period there were no trends in the soil temperature at 10 cm depth and NDWI.
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