| 1. |
- Elmendorf, Sarah C., et al.
(författare)
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Plot-scale evidence of tundra vegetation change and links to recent summer warming
- 2012
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Ingår i: Nature Climate Change. - : Nature Publishing Group. - 1758-678X .- 1758-6798. ; 2:6, s. 453-457
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Tidskriftsartikel (refereegranskat)abstract
- Temperature is increasing at unprecedented rates across most of the tundra biome. Remote-sensing data indicate that contemporary climate warming has already resulted in increased productivity over much of the Arctic, but plot-based evidence for vegetation transformation is not widespread. We analysed change in tundra vegetation surveyed between 1980 and 2010 in 158 plant communities spread across 46 locations.We found biome-wide trends of increased height of the plant canopy and maximum observed plant height for most vascular growth forms; increased abundance of litter; increased abundance of evergreen, low-growing and tall shrubs; and decreased abundance of bare ground. Intersite comparisons indicated an association between the degree of summer warming and change in vascular plant abundance, with shrubs, forbs and rushes increasing with warming. However, the association was dependent on the climate zone, the moisture regime and the presence of permafrost. Our data provide plot-scale evidence linking changes in vascular plant abundance to local summer warming in widely dispersed tundra locations across the globe.
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| 2. |
- Björk, Robert G., 1974, et al.
(författare)
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Climate-related soil changes in tundra ecosystems at Latnjajaure, northern Sweden – an ITEX-IPY project
- 2010
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Ingår i: International Polar Year Oslo Science Conference.
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Konferensbidrag (refereegranskat)abstract
- During the 90'ies, the International Tundra Experiment (ITEX) was established as a leading project in arctic and alpine ecology, and has become a model for many later network establishments. The present study capitalizes on the early efforts of ITEX and aims at assessing ecosystem changes in the alpine areas of northern Sweden above timberline, i.e. the tundra, in relation to global change. By using the "old" ITEX plots established during the early years of the program we have measured ecosystem respiration (ER), the Normalized Difference Vegetation Index, and nitrogen (N) mineralization over the growing season. In addition, have soil samples been taken to quantify changes in the carbon (C) and N pool, including 13C and 15N. After 12 to 15 years of open top chamber (OTC) treatment no statistical effect was found on the soil temperature (10 cm soil depth), although the was an overall increase in all OTC by +0.2°C. However, the soil moisture decreased significantly by 3-14%, depending on plant community, in the OTCs compared to ambient conditions. Preliminary, there was a 20-37% non-significant higher mean ER in the OTC compared to the ambient plots over the growing season. Furthermore, the OTC treatment did not affect the growing season mineralization of inorganic N, or total C and N content of the soil. The stable isotope data showed both enrichment and depletion as a consequence of the OTC treatment, but no general pattern was discerned. Thus, this non-significant higher ER is most likely of plant origin than soil, as the plant standing biomass has increased in the OTCs. This study does not support the current consensus that tundra soils will alter their C and N dynamics in response to climate change.
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| 3. |
- Butterfield, B. J., et al.
(författare)
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Alpine cushion plants inhibit the loss of phylogenetic diversity in severe environments
- 2013
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Ingår i: Ecology Letters. - : Wiley. - 1461-0248 .- 1461-023X. ; 16:4, s. 478-486
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Tidskriftsartikel (refereegranskat)abstract
- Biotic interactions can shape phylogenetic community structure (PCS). However, we do not know how the asymmetric effects of foundation species on communities extend to effects on PCS. We assessed PCS of alpine plant communities around the world, both within cushion plant foundation species and adjacent open ground, and compared the effects of foundation species and climate on alpha (within-microsite), beta (between open and cushion) and gamma (open and cushion combined) PCS. In the open, alpha PCS shifted from highly related to distantly related with increasing potential productivity. However, we found no relationship between gamma PCS and climate, due to divergence in phylogenetic composition between cushion and open sub-communities in severe environments, as demonstrated by increasing phylo-beta diversity. Thus, foundation species functioned as micro-refugia by facilitating less stress-tolerant lineages in severe environments, erasing a global productivity – phylogenetic diversity relationship that would go undetected without accounting for this important biotic interaction.
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| 4. |
- Cavieres, Lohengrin A., et al.
(författare)
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Facilitative plant interactions and climate simultaneously drive alpine plant diversity
- 2014
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Ingår i: Ecology Letters. - : Wiley. - 1461-0248 .- 1461-023X. ; 17:2, s. 193-202
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Tidskriftsartikel (refereegranskat)abstract
- Interactions among species determine local-scale diversity, but local interactions are thought to have minor effects at larger scales. However, quantitative comparisons of the importance of biotic interactions relative to other drivers are rarely made at larger scales. Using a data set spanning 78 sites and five continents, we assessed the relative importance of biotic interactions and climate in determining plant diversity in alpine ecosystems dominated by nurse-plant cushion species. Climate variables related with water balance showed the highest correlation with richness at the global scale. Strikingly, although the effect of cushion species on diversity was lower than that of climate, its contribution was still substantial. In particular, cushion species enhanced species richness more in systems with inherently impoverished local diversity. Nurse species appear to act as a ‘safety net’ sustaining diversity under harsh conditions, demonstrating that climate and species interactions should be integrated when predicting future biodiversity effects of climate change.
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| 5. |
- Elmendorf, Sarah C., et al.
(författare)
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Global assessment of experimental climate warming on tundra vegetation : heterogeneity over space and time
- 2012
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Ingår i: Ecology Letters. - : Wiley. - 1461-023X .- 1461-0248. ; 15:2, s. 164-175
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Forskningsöversikt (refereegranskat)abstract
- Understanding the sensitivity of tundra vegetation to climate warming is critical to forecasting future biodiversity and vegetation feedbacks to climate. In situ warming experiments accelerate climate change on a small scale to forecast responses of local plant communities. Limitations of this approach include the apparent site-specificity of results and uncertainty about the power of short-term studies to anticipate longer term change. We address these issues with a synthesis of 61 experimental warming studies, of up to 20 years duration, in tundra sites worldwide. The response of plant groups to warming often differed with ambient summer temperature, soil moisture and experimental duration. Shrubs increased with warming only where ambient temperature was high, whereas graminoids increased primarily in the coldest study sites. Linear increases in effect size over time were frequently observed. There was little indication of saturating or accelerating effects, as would be predicted if negative or positive vegetation feedbacks were common. These results indicate that tundra vegetation exhibits strong regional variation in response to warming, and that in vulnerable regions, cumulative effects of long-term warming on tundra vegetation and associated ecosystem consequences have the potential to be much greater than we have observed to date.
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| 6. |
- Andresen, Louise C., 1974, et al.
(författare)
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Free amino acids in the rhizosphere
- 2014
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Ingår i: 19th European Nitrogen Cycle Meeting. September 10-12th 2014, Gent, Belgium.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)
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| 7. |
- Björk, Robert G., 1974, et al.
(författare)
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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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Ingår i: FEMS Microbiology Ecology. - : Oxford University Press (OUP). - 1574-6941 .- 0168-6496. ; 73:3, s. 550-562
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Tidskriftsartikel (refereegranskat)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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| 8. |
- Björk, Robert G., 1974
(författare)
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Ectomycorrhizal mycelia production in a forested peatland: effects on greenhouse gas fluxes
- 2012
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Ingår i: 4th COST meeting ‘Belowground carbon in European forest’, Antalya, Turkey, 28–31 October 2012.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- The role of ectomycorrhizal fungi in key ecosystem processes such as C sequestration and greenhouse gas (GHG) fluxes is surprisingly poorly understood, even though they are undoubtedly of major significance. In this study we have measured the production and isotopic signature of extramatrical mycelium (EMM) of mycorrhizal fungi since 2007 using in-growth mesh bags. We also conducted a trenching experiment, where 50 µm (permit EMM but not roots) or 1 µm (excludes both EMM and roots) mesh was used. Soil respiration was measured using an automatic chamber system, and nitrous oxide (N2O) and methane (CH4) using a closed chamber technique. In general, the EMM production in the peat soil was low compared to other soils, but also varied much between years (from 0.03 to 4.09 g C m-2). The EMM production was also 2 to 6 times higher in the top 10 cm compared to 10-20 cm soil depth depending of year. Over the growing season the EMM production peaked in August, a few weeks before the main sporocarp season. The mycelial delta values also varied with several ‰ within season as well as between years. Interestingly, the δ15N but not the δ13C of the mycelia changed with depth and the differences relative to the SOM were inconsistent. Although the EMM production in the peat soil is low it had a major impact on GHG emissions from the soil. In 2009, the contribution from autotrophic mycelia respiration was 10% of the annual CO2 emissions, while autotrophic root respiration contributed with 23%. This means that 2/3 of the annual CO2 emissions are originated from heterotrophic respiration at this site. For N2O, 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. The results of the study emphasize the importance of ectomycorrhiza in regulating GHG emissions from forested organic soils.
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| 9. |
- Björk, Robert G., 1974, et al.
(författare)
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Extramatrical mycelia production and turnover in two drained Norway spruce forests
- 2010
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Ingår i: 1st COST meeting ‘Belowground carbon in Europeanforest’, Birmensdorf, Switzerland, 26–28 January 2010..
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Root systems form important associations with fungi, so called mycorrhiza, which in spruce forests are dominated by ectomycorrhiza. Ectomycorrhizal fungi is functionally important in water and nutrient capture, and therefore probably have major influence on the overall ecosystem functioning. In addition to transferring water and nutrient to its host plant the fungus receive photosynthetic C. The extramatrical mycelium (EMM) is thereby an important sink for carbon in boreal forests, but estimation of the actual EMM production is rare. The objective was to quantify the annual and seasonal production and turnover of EMM in two drained coniferous soils. The study was conducted in two Norway spruce stands at Skogaryd Research Forest, southwest Sweden. One of the sites was a mineral soil (“the mineral site”), with high organic content, and affor-ested in 1962. The other site was a peat soil of minerotrophic origin (“the peat site”), drained in the 1870s and afforested in 1951. In-growth tubes (10-20 cm long) were used to estimate EMM production and turnover through sequential harvesting during 2007-2009. Preliminary results show a higher EMM production at the mineral site than at the peat site. At the peat site the annual EMM production varied largely between years, 0.1-10.1 gdw m-2 (no annual data are currently available for the mineral site). Interestingly, a significant EMM production from December to 15th of June at the mineral site was found, most likely occurring during late May-early June. How-ever, the major EMM production (21-53 mg m-2 d-1) occurred mid-August to mid-September at both sites. It was not possible to calculate an EMM turnover the first two years due to the large spatial vari-ability. Our study suggests that high EMM production coincides with fine root production, and can equal one-fourth of belowground production. However, the large spatial variability in EMM production accentuates the need to increase within sub-site replication.
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| 10. |
- Björk, Robert G., 1974, et al.
(författare)
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Long-term warming effects on carbon and nitrogen dynamics in tundra soils
- 2012
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Ingår i: 20th Anniversary ITEX Workshop, El Paso, USA, 17–21 January 2012.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- During IPY 2008 we used the ITEX experiment in Latnjajaure (northern Sweden), established during the early years of the program, to investigate long-term warming effects on ecosystem respiration (ER), carbon (C) and nitrogen (N) pool (including d13C and d15N), soil organic C (SOC) chemical composition, and N mineralization among plant communities. After 12 to 15 years of open top chamber (OTC) treatment no statistical effect was found on the soil temperature (10 cm soil depth), although the was an overall increase in all OTC by +0.2°C. However, the soil moisture decreased significantly by 3-14%, depending on plant community, in the OTCs compared to ambient conditions. Preliminary, there was a 19-61% non-significant increase in annual growing season ER in the OTC compared to the ambient plots over the growing season. The were distinct differences in the SOM functional composition among plant communities with c 10% more O-alkyls stored in tussock tundra than in dry meadow. The OTCs did not consistently alter the SOM composition among the vegetation types but clearly showed a trend for reduced aliphatic and O-alkyl C in the OTCs suggesting increased decomposition (or reduced inputs) of these compounds. Thus, the non-significantly higher ER may in some communities be of plant origin linked to greater plant biomass in the OTCs, and in other (e.g. tussock tundra) from increased decomposition rates. In conclusion, this study showed that 12-15 years of OTC treatment had a modest effects impact C and N dynamics in tundra soils specific to distinct plant communities.
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