| 1. |
- 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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| 2. |
- Bokhorst, Stef Frederik, et al.
(författare)
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Variable temperature effects of Open Top Chambers at polar and alpine sites explained by irradiance and snow depth
- 2013
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Ingår i: Global Change Biology. - : Wiley. - 1354-1013 .- 1365-2486. ; 19:1, s. 64-74
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Forskningsöversikt (refereegranskat)abstract
- Environmental manipulation studies are integral to determining biological consequences of climate warming. Open Top Chambers (OTCs) have been widely used to assess summer warming effects on terrestrial biota, with their effects during other seasons normally being given less attention even though chambers are often deployed year-round. In addition, their effects on temperature extremes and freeze-thaw events are poorly documented. To provide robust documentation of the microclimatic influences of OTCs throughout the year, we analysed temperature data from 20 studies distributed across polar and alpine regions. The effects of OTCs on mean temperature showed a large range (-0.9 to 2.1 degrees C) throughout the year, but did not differ significantly between studies. Increases in mean monthly and diurnal temperature were strongly related (R-2 = 0.70) with irradiance, indicating that PAR can be used to predict the mean warming effect of OTCs. Deeper snow trapped in OTCs also induced higher temperatures at soil/vegetation level. OTC-induced changes in the frequency of freeze-thaw events included an increase in autumn and decreases in spring and summer. Frequency of high-temperature events in OTCs increased in spring, summer and autumn compared with non-manipulated control plots. Frequency of low-temperature events was reduced by deeper snow accumulation and higher mean temperatures. The strong interactions identified between aspects of ambient environmental conditions and effects of OTCs suggest that a detailed knowledge of snow depth, temperature and irradiance levels enables us to predict how OTCs will modify the microclimate at a particular site and season. Such predictive power allows a better mechanistic understanding of observed biotic response to experimental warming studies and for more informed design of future experiments. However, a need remains to quantify OTC effects on water availability and wind speed (affecting, for example, drying rates and water stress) in combination with microclimate measurements at organism level.
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| 3. |
- Handa, I. Tanya, et al.
(författare)
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Consequences of biodiversity loss for litter decomposition across biomes
- 2014
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Ingår i: Nature. - : Springer Science and Business Media LLC. - 0028-0836 .- 1476-4687. ; 509:7499, s. 218-221
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Tidskriftsartikel (refereegranskat)abstract
- The decomposition of dead organic matter is a major determinant of carbon and nutrient cycling in ecosystems, and of carbon fluxes between the biosphere and the atmosphere(1-3). Decomposition is driven by a vast diversity of organisms that are structured in complex food webs(2,4). Identifying the mechanisms underlying the effects of biodiversity on decomposition is critical(4-6) given the rapid loss of species worldwide and the effects of this loss on human well-being(7-9). Yet despite comprehensive syntheses of studies on how biodiversity affects litter decomposition(4-6,10), key questions remain, including when, where and how biodiversity has a role and whether general patterns and mechanisms occur across ecosystems and different functional types of organism(4,9-12). Here, in field experiments across five terrestrial and aquatic locations, ranging from the subarctic to the tropics, we show that reducing the functional diversity of decomposer organisms and plant litter types slowed the cycling of litter carbon and nitrogen. Moreover, we found evidence of nitrogen transfer from the litter of nitrogen-fixing plants to that of rapidly decomposing plants, but not between other plant functional types, highlighting that specific interactions in litter mixtures control carbon and nitrogen cycling during decomposition. The emergence of this general mechanism and the coherence of patterns across contrasting terrestrial and aquatic ecosystems suggest that biodiversity loss has consistent consequences for litter decomposition and the cycling of major elements on broad spatial scales.
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| 4. |
- Keuper, Frida, et al.
(författare)
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A frozen feast : thawing permafrost increases plant-available nitrogen in subarctic peatlands
- 2012
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Ingår i: Global Change Biology. - : Wiley. - 1354-1013 .- 1365-2486. ; 18:6, s. 1998-2007
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Tidskriftsartikel (refereegranskat)abstract
- Many of the world's northern peatlands are underlain by rapidly thawing permafrost. Because plant production in these peatlands is often nitrogen (N)-limited, a release of N stored in permafrost may stimulate net primary production or change species composition if it is plant-available. In this study, we aimed to quantify plant-available N in thawing permafrost soils of subarctic peatlands. We compared plant-available N-pools and -fluxes in near-surface permafrost (010cm below the thawfront) to those taken from a current rooting zone layer (515cm depth) across five representative peatlands in subarctic Sweden. A range of complementary methods was used: extractions of inorganic and organic N, inorganic and organic N-release measurements at 0.5 and 11 degrees C (over 120days, relevant to different thaw-development scenarios) and a bioassay with Poa alpina test plants. All extraction methods, across all peatlands, consistently showed up to seven times more plant-available N in near-surface permafrost soil compared to the current rooting zone layer. These results were supported by the bioassay experiment, with an eightfold larger plant N-uptake from permafrost soil than from other N-sources such as current rooting zone soil or fresh litter substrates. Moreover, net mineralization rates were much higher in permafrost soils compared to soils from the current rooting zone layer (273mgNm-2 and 1348mgNm-2 per growing season for near-surface permafrost at 0.5 degrees C and 11 degrees C respectively, compared to -30mgNm-2 for current rooting zone soil at 11 degrees C). Hence, our results demonstrate that near-surface permafrost soil of subarctic peatlands can release a biologically relevant amount of plant available nitrogen, both directly upon thawing as well as over the course of a growing season through continued microbial mineralization of organically bound N. Given the nitrogen-limited nature of northern peatlands, this release may have impacts on both plant productivity and species composition.
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| 5. |
- Keuper, Frida, et al.
(författare)
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A race for space? : How Sphagnum fuscumstabilizes vegetation composition during long-termclimate manipulations
- 2011
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Ingår i: Global Change Biology. - : Blackwell. - 1354-1013 .- 1365-2486. ; 17:6, s. 2162-2171
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Tidskriftsartikel (refereegranskat)abstract
- Strong climate warming is predicted at higher latitudes this century, with potentially major consequences forproductivity and carbon sequestration. Although northern peatlands contain one-third of the world’s soil organiccarbon, little is known about the long-term responses to experimental climate change of vascular plant communities inthese Sphagnum-dominated ecosystems.We aimed to see how long-term experimental climate manipulations, relevantto different predicted future climate scenarios, affect total vascular plant abundance and species composition whenthe community is dominated by mosses. During 8 years, we investigated how the vascular plant community of aSphagnum fuscum-dominated subarctic peat bog responded to six experimental climate regimes, including factorialcombinations of summer as well as spring warming and a thicker snow cover. Vascular plant species composition inour peat bog was more stable than is typically observed in (sub)arctic experiments: neither changes in total vascularplant abundance, nor in individual species abundances, Shannon’s diversity or evenness were found in response tothe climate manipulations. For three key species (Empetrum hermaphroditum, Betula nana and S. fuscum) we alsomeasured whether the treatments had a sustained effect on plant length growth responses and how these responsesinteracted. Contrasting with the stability at the community level, both key shrubs and the peatmoss showed sustainedpositive growth responses at the plant level to the climate treatments. However, a higher percentage of mossencroachedE. hermaphroditum shoots and a lack of change in B. nana net shrub height indicated encroachment byS. fuscum, resulting in long-term stability of the vascular community composition: in a warmer world, vascular speciesof subarctic peat bogs appear to just keep pace with growing Sphagnum in their race for space. Our findings contributeto general ecological theory by demonstrating that community resistance to environmental changes does notnecessarily mean inertia in vegetation response.
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| 6. |
- Keuper, Frida, et al.
(författare)
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Tundra in the rain : Differential vegetation responses to three years of experimentally doubled summer precipitation in Siberian shrub and Swedish bog tundra
- 2012
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Ingår i: Ambio. - : Springer Netherlands. - 0044-7447 .- 1654-7209. ; 41:Suppl. 3, s. 269-280
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Tidskriftsartikel (refereegranskat)abstract
- Precipitation amounts and patterns at high latitude sites have been predicted to change as a result of global climatic changes. We addressed vegetation responses to three years of experimentally increased summer precipitation in two previously unaddressed tundra types: Betula nana-dominated shrub tundra (northeast Siberia) and a dry Sphagnum fuscum-dominated bog (northern Sweden). Positive responses to approximately doubled ambient precipitation (an increase of 200 mm year(-1)) were observed at the Siberian site, for B. nana (30 % larger length increments), Salix pulchra (leaf size and length increments) and Arctagrostis latifolia (leaf size and specific leaf area), but none were observed at the Swedish site. Total biomass production did not increase at either of the study sites. This study corroborates studies in other tundra vegetation types and shows that despite regional differences at the plant level, total tundra plant productivity is, at least at the short or medium term, largely irresponsive to experimentally increased summer precipitation.
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| 7. |
- Krab, Eveline J., et al.
(författare)
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Northern peatland Collembola communities unaffected by three summers of simulated extreme precipitation
- 2014
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Ingår i: Agriculture, Ecosystems & Environment. Applied Soil Ecology. - : Elsevier BV. - 0929-1393 .- 1873-0272. ; 79, s. 70-76
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Tidskriftsartikel (refereegranskat)abstract
- Extreme climate events are observed and predicted to increase in frequency and duration in high-latitudeecosystems as a result of global climate change. This includes extreme precipitation events, which maydirectly impact on belowground food webs and ecosystem functioning by their physical impacts and byaltering local soil moisture conditions.We assessed responses of the Collembola community in a northern Sphagnum fuscum-dominatedombrotrophic peatland to three years of experimentally increased occurrence of extreme precipitationevents. Annual summer precipitation was doubled (an increase of 200 mm) by 16 simulated extremerain events within the three months growing season, where on each occasion 12.5 mm of rain was addedwithin a few minutes. Despite this high frequency and intensity of the rain events, no shifts in Collemboladensity, relative species abundances and community weighted means of three relevant traits (moisturepreference, vertical distribution and body size) were observed. This strongly suggests that the peatlandCollembola community is unaffected by the physical impacts of extreme precipitation and the short-termvariability in moisture conditions. The lack of response is most likely reinforced by the fact that extremeprecipitation events do not seem to alter longer-term soil moisture conditions in the peat layers inhabitedby soil fauna.This study adds evidence to the observation that the biotic components of northern ombrotrophicpeatlands are hardly responsive to an increase in extreme summer precipitation events. Given the importance of these ecosystems for the global C balance, these findings significantly contribute to the currentknowledge of the ecological impact of future climate scenarios. (C) 2014 Elsevier B.V. All rights reserved.
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