| 1. |
- Beecham, Ashley H, et al.
(author)
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Analysis of immune-related loci identifies 48 new susceptibility variants for multiple sclerosis.
- 2013
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In: Nature genetics. - : Springer Science and Business Media LLC. - 1546-1718 .- 1061-4036. ; 45:11, s. 1353-60
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Journal article (peer-reviewed)abstract
- Using the ImmunoChip custom genotyping array, we analyzed 14,498 subjects with multiple sclerosis and 24,091 healthy controls for 161,311 autosomal variants and identified 135 potentially associated regions (P < 1.0 × 10(-4)). In a replication phase, we combined these data with previous genome-wide association study (GWAS) data from an independent 14,802 subjects with multiple sclerosis and 26,703 healthy controls. In these 80,094 individuals of European ancestry, we identified 48 new susceptibility variants (P < 5.0 × 10(-8)), 3 of which we found after conditioning on previously identified variants. Thus, there are now 110 established multiple sclerosis risk variants at 103 discrete loci outside of the major histocompatibility complex. With high-resolution Bayesian fine mapping, we identified five regions where one variant accounted for more than 50% of the posterior probability of association. This study enhances the catalog of multiple sclerosis risk variants and illustrates the value of fine mapping in the resolution of GWAS signals.
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| 2. |
- Sundqvist, Maja K., et al.
(author)
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Chemical properties of plant litter in response to elevation : subarctic vegetation challenges phenolic allocation theories
- 2012
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In: Functional Ecology. - : John Wiley & Sons. - 0269-8463 .- 1365-2435. ; 26:5, s. 1090-1099
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Journal article (peer-reviewed)abstract
- Several theories predict that increasing stress (e.g. decreasing nutrient availability or decreasing temperature) should result in higher amounts of plant phenolic compounds both at the interspecific and intraspecific levels. Further, several theories predict that plant phenolics are major drivers of plantsoil feedbacks whereby they influence litter decomposition rates and the return of nutrients to plants. We investigated the potential influence of shifts in abiotic factors on litter phenolic properties using an elevational gradient in northern Sweden, for which temperature and soil fertility decline with increasing elevation. The system consists of two vegetation types: heath, (associated with low soil fertility) and meadow (associated with higher fertility), which occur across the entire gradient. We hypothesized that total phenolics, tannins and protein complexation capacity (PCC) of leaf litter would increase with elevation within and among plant species. We further hypothesized that at the whole-plot level (using community-weighted averages), these properties would be higher in heath than meadow, and that phenolic properties for meadow vegetation would show stronger responses to elevation than for heath. We measured phenolic properties in leaf litter for 13 species from both vegetation types across an established elevational gradient (500-1000m) in Swedish subarctic tundra. Contrary to our hypotheses, different species showed highly contrasting responses in their phenolic characteristics to elevation. At the across-species level, total phenolic content in litter decreased with elevation. At the whole-plot level, tannin concentrations were higher for the heath than for the meadow, whereas total phenolics and PCC did not differ. However, consistent with our hypothesis, our results showed that phenolic properties were more responsive to elevation for the meadow compared to the heath, as a consequence of greater species turnover for the meadow. Our results are inconsistent with theories predicting higher plant phenolic concentrations with increasing environmental stress or decreasing nutrient availability. They also provide evidence that across abiotic gradients in the subarctic tundra, there are large shifts in litter phenolic properties (including those that are able to complex protein) and highlight that the direction and strength of such shifts may differ greatly among vegetation types.
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| 3. |
- Sundqvist, Maja K., et al.
(author)
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Contrasting nitrogen and phosphorus dynamics across an elevational gradient for subarctic tundra heath and meadow vegetation
- 2014
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In: Plant and Soil. - : Springer Netherlands. - 0032-079X .- 1573-5036. ; 383:1-2, s. 387-399
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Journal article (peer-reviewed)abstract
- This study explores soil nutrient cycling processes and microbial properties for two contrasting vegetation types along an elevational gradient in subarctic tundra to improve our understanding of how temperature influences nutrient availability in an ecosystem predicted to be sensitive to global warming. We measured total amino acid (Amino-N), mineral nitrogen (N) and phosphorus (P) concentrations, in situ net N and P mineralization, net Amino-N consumption, and microbial biomass C, N and P in both heath and meadow soils across an elevational gradient near Abisko, Sweden. For the meadow, NH4 (+) concentrations and net N mineralization were highest at high elevations and microbial properties showed variable responses; these variables were largely unresponsive to elevation for the heath. Amino-N concentrations sometimes showed a tendency to increase with elevation and net Amino-N consumption was often unresponsive to elevation. Overall, PO4-P concentrations decreased with elevation and net P immobilization mostly occurred at lower elevations; these effects were strongest for the heath. Our results reveal that elevation-associated changes in temperature can have contrasting effects on the cycling of N and P in subarctic soils, and that the strength and direction of these effects depend strongly on dominant vegetation type.
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| 4. |
- Sundqvist, Maja K., et al.
(author)
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Interactive effects of vegetation type and elevation on aboveground and belowground properties in a subarctic tundra
- 2011
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In: Oikos. - Copenhagen : Munksgaard. - 0030-1299 .- 1600-0706. ; 120:1, s. 128-142
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Journal article (peer-reviewed)abstract
- An improved knowledge of how contrasting types of plant communities and their associated soil biota differ in their responses to climatic variables is important for better understanding the future impacts of climate change on terrestrial ecosystems. Elevational gradients serve as powerful study systems for answering questions on how ecological processes can be affected by changes in temperature and associated climatic variables. In this study, we evaluated how plant and soil microbial communities, and abiotic soil properties, change with increasing elevation in subarctic tundra in northern Sweden, for each of two dominant but highly contrasting vegetation types, namely heath (dominated by woody dwarf shrubs) and meadow (dominated by herbaceous species). To achieve this, we measured plant community characteristics, microbial community properties and several soil abiotic properties for both vegetation types across an elevation gradient of 500 to 1000 m. We found that the two vegetation types differed not only in several above- and belowground properties, but also in how these properties responded to elevation, pointing to important interactive effects between vegetation type and elevation. Specifically, for the heath, available soil nitrogen and phosphorus decreased with elevation whereas fungal dominance increased, while for the meadow, idiosyncratic responses to elevation for these variables were found. These differences in belowground responses to elevation among vegetation types were linked to shifts in the species and functional group composition of the vegetation. Our results highlight that these two dominant vegetation types in subarctic tundra differ greatly not only in fundamental aboveground and belowground properties, but also in how these properties respond to elevation and are therefore likely to be influenced by temperature. As such they highlight that vegetation type, and the soil abiotic properties that determine this, may serve as powerful determinants of how both aboveground and belowground properties respond to strong environmental gradients.
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| 5. |
- Sundqvist, Maja K., et al.
(author)
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Plant and microbial responses to nitrogen and phosphorus addition across an elevational gradient in subarctic tundra
- 2014
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In: Ecology. - : Wiley. - 0012-9658 .- 1939-9170. ; 95:7, s. 1819-1835
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Journal article (peer-reviewed)abstract
- Temperature and nutrients are major limiting factors in subarctic tundra. Experimental manipulation of nutrient availability along elevational gradients (and thus temperature) can improve our understanding of ecological responses to climate change. However, no study to date has explored impacts of nutrient addition along a tundra elevational gradient, or across contrasting vegetation types along any elevational gradient. We set up a full factorial nitrogen (N) and phosphorus (P) fertilization experiment in each of two vegetation types (heath and meadow) at 500 m, 800 m, and 1000 m elevation in northern Swedish tundra. We predicted that plant and microbial communities in heath or at lower elevations would be more responsive to N addition while communities in meadow or at higher elevations would be more responsive to P addition, and that fertilizer effects would vary more with elevation for the heath than for the meadow. Although our results provided little support for these predictions, the relationship between nutrient limitation and elevation differed between vegetation types. Most plant and microbial properties were responsive to N and/or P fertilization, but responses often varied with elevation and/or vegetation type. For instance, vegetation density significantly increased with N + P fertilization relative to the other fertilizer treatments, and this increase was greatest at the lowest elevation for the heath but at the highest elevation for the meadow. Arbuscular mycorrhizae decreased with P fertilization at 500 m for the meadow, but with all fertilizer treatments in both vegetation types at 800 m. Fungal to bacterial ratios were enhanced by N + P fertilization for the two highest elevations in the meadow only. Additionally, microbial responses to fertilization were primarily direct rather than indirect via plant responses, pointing to a decoupled response of plant and microbial communities to nutrient addition and elevation. Because our study shows how two community types differ in their responses to fertilization and elevation, and because the temperature range across this gradient is similar to 3 degrees C, our study is informative about how nutrient limitation in tundra may be influenced by temperature shifts that are comparable to those expected under climate change during this century.
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| 6. |
- Sundqvist, Maja K., et al.
(author)
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Within- and across-species responses of plant traits and litter decomposition to elevation across contrasting vegetation types in subarctic tundra
- 2011
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In: PLOS ONE. - : Plos one. - 1932-6203. ; 6:10, s. e27056-
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Journal article (peer-reviewed)abstract
- Elevational gradients are increasingly recognized as a valuable tool for understanding how community and ecosystem properties respond to climatic factors, but little is known about how plant traits and their effects on ecosystem processes respond to elevation. We studied the response of plant leaf and litter traits, and litter decomposability across a gradient of elevation, and thus temperature, in subarctic tundra in northern Sweden for each of two contrasting vegetation types, heath and meadow, dominated by dwarf shrubs and herbaceous plants respectively. This was done at each of three levels; across species, within individual species, and the plant community using a community weighted average approach. Several leaf and litter traits shifted with increasing elevation in a manner consistent with greater conservation of nutrients at all three levels, and the most consistent response was an increase in tissue N to P ratio. However, litter decomposition was less directly responsive to elevation because the leaf and litter traits which were most responsive to elevation were not necessarily those responsible for driving decomposition. At the community level, the response to elevation of foliar and litter traits, and decomposability, varied greatly among the two vegetation types, highlighting the importance of vegetation type in determining ecological responses to climatic factors such as temperature. Finally our results highlight how understanding the responses of leaf and litter characteristics of functionally distinct vegetation types, and the processes that they drive, to temperature helps provide insights about how future climate change could affect tundra ecosystems.
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| 7. |
- Vincent, Andrea G., et al.
(author)
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Bioavailable Soil Phosphorus Decreases with Increasing Elevation in a Subarctic Tundra Landscape
- 2014
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In: PLOS ONE. - : PLOS one. - 1932-6203. ; 9:3, s. e92942-
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Journal article (peer-reviewed)abstract
- Phosphorus (P) is an important macronutrient in arctic and subarctic tundra and its bioavailability is regulated by the mineralization of organic P. Temperature is likely to be an important control on P bioavailability, although effects may differ across contrasting plant communities with different soil properties. We used an elevational gradient in northern Sweden that included both heath and meadow vegetation types at all elevations to study the effects of temperature, soil P sorption capacity and oxalate-extractable aluminium (Al-ox) and iron (Fe-ox) on the concentration of different soil P fractions. We hypothesized that the concentration of labile P fractions would decrease with increasing elevation (and thus declining temperature), but would be lower in meadow than in heath, given that N to P ratios in meadow foliage are higher. As expected, labile P in the form of Resin-P declined sharply with elevation for both vegetation types. Meadow soils did not have lower concentrations of Resin-P than heath soils, but they did have 2-fold and 1.5-fold higher concentrations of NaOH-extractable organic P and Residual P, respectively. Further, meadow soils had 3-fold higher concentrations of Al-ox + Feox and a 20% higher P sorption index than did heath soils. Additionally, Resin-P expressed as a proportion of total soil P for the meadow was on average half that in the heath. Declining Resin-P concentrations with elevation were best explained by an associated 2.5-3.0 degrees C decline in temperature. In contrast, the lower P availability in meadow relative to heath soils may be associated with impaired organic P mineralization, as indicated by a higher accumulation of organic P and P sorption capacity. Our results indicate that predicted temperature increases in the arctic over the next century may influence P availability and biogeochemistry, with consequences for key ecosystem processes limited by P, such as primary productivity.
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