| 1. |
- Hicks, Lettice C., et al.
(författare)
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Simulated rhizosphere deposits induce microbial N-mining that may accelerate shrubification in the subarctic
- 2020
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Ingår i: Ecology. - : Wiley. - 0012-9658 .- 1939-9170. ; 101:9
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Tidskriftsartikel (refereegranskat)abstract
- Climate change is exposing high-latitude systems to warming and a shift towards more shrub-dominated plant communities, resulting in increased leaf-litter inputs at the soil surface, and more labile root-derived organic matter (OM) input in the soil profile. Labile OM can stimulate the mineralization of soil organic matter (SOM); a phenomenon termed “priming.” In N-poor subarctic soils, it is hypothesized that microorganisms may “prime” SOM in order to acquire N (microbial N-mining). Increased leaf-litter inputs with a high C/N ratio might further exacerbate microbial N demand, and increase the susceptibility of N-poor soils to N-mining. We investigated the N-control of SOM mineralization by amending soils from climate change–simulation treatments in the subarctic (+1.1°C warming, birch litter addition, willow litter addition, and fungal sporocarp addition) with labile OM either in the form of glucose (labile C; equivalent to 400 µg C/g fresh [fwt] soil) or alanine (labile C + N; equivalent to 400 µg C and 157 µg N/g fwt soil), to simulate rhizosphere inputs. Surprisingly, we found that despite 5 yr of simulated climate change treatments, there were no significant effects of the field-treatments on microbial process rates, community structure or responses to labile OM. Glucose primed the mineralization of both C and N from SOM, but gross mineralization of N was stimulated more than that of C, suggesting that microbial SOM use increased in magnitude and shifted to components richer in N (i.e., selective microbial N-mining). The addition of alanine also resulted in priming of both C and N mineralization, but the N mineralization stimulated by alanine was greater than that stimulated by glucose, indicating strong N-mining even when a source of labile OM including N was supplied. Microbial carbon use efficiency was reduced in response to both labile OM inputs. Overall, these findings suggest that shrub expansion could fundamentally alter biogeochemical cycling in the subarctic, yielding more N available for plant uptake in these N-limited soils, thus driving positive plant–soil feedbacks.
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| 2. |
- Berner, Logan T., et al.
(författare)
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The Arctic plant aboveground biomass synthesis dataset
- 2024
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Ingår i: Scientific Data. - : Springer Nature. - 2052-4463. ; 11:1
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Tidskriftsartikel (refereegranskat)abstract
- Plant biomass is a fundamental ecosystem attribute that is sensitive to rapid climatic changes occurring in the Arctic. Nevertheless, measuring plant biomass in the Arctic is logistically challenging and resource intensive. Lack of accessible field data hinders efforts to understand the amount, composition, distribution, and changes in plant biomass in these northern ecosystems. Here, we present The Arctic plant aboveground biomass synthesis dataset, which includes field measurements of lichen, bryophyte, herb, shrub, and/or tree aboveground biomass (g m−2) on 2,327 sample plots from 636 field sites in seven countries. We created the synthesis dataset by assembling and harmonizing 32 individual datasets. Aboveground biomass was primarily quantified by harvesting sample plots during mid- to late-summer, though tree and often tall shrub biomass were quantified using surveys and allometric models. Each biomass measurement is associated with metadata including sample date, location, method, data source, and other information. This unique dataset can be leveraged to monitor, map, and model plant biomass across the rapidly warming Arctic.
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| 3. |
- Cruz-Paredes, Carla, et al.
(författare)
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Wood ash application in a managed Norway spruce plantation did not affect ectomycorrhizal diversity or N retention capacity
- 2019
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Ingår i: Fungal Ecology. - : Elsevier BV. - 1754-5048. ; 39, s. 1-11
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Tidskriftsartikel (refereegranskat)abstract
- Ectomycorrhizal (ECM) fungi are key players in N cycling in coniferous forests, and forest management such as application of wood ash can affect their functionality. The aim of this study was to determine the effects of wood ash application on ECM fungal mycelial production, capacity to retain N, diversity and community composition. In-growth mesh bags were installed in control and treated plots. After 6 months, 15N labeled ammonium and nitrate were applied into the mesh bags, and 24 h later extramatrical mycelium (EMM) was extracted and analyzed. Wood ash had no effects on EMM in-growth, N retention capacity, diversity or community composition. In contrast, there were significant seasonal differences in the amount of EMM produced. These results demonstrate that applying up to 6 t ha−1 of wood ash in this type of plantation forest is a safe management practice that does not increase N leaching or negatively affect ECM fungi.
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| 4. |
- Kristensen, Jeppe A., et al.
(författare)
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Background insect herbivory increases with local elevation but makes minor contribution to element cycling along natural gradients in the Subarctic
- 2020
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Ingår i: Ecology and Evolution. - : John Wiley & Sons. - 2045-7758. ; 10:20, s. 11684-11698
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Tidskriftsartikel (refereegranskat)abstract
- Herbivores can exert major controls over biogeochemical cycling. As invertebrates are highly sensitive to temperature shifts (ectothermal), the abundances of insects in high-latitude systems, where climate warming is rapid, is expected to increase. In subarctic mountain birch forests, research has focussed on geometrid moth outbreaks, while the contribution of background insect herbivory (BIH) to elemental cycling is poorly constrained. In northern Sweden, we estimated BIH along 9 elevational gradients distributed across a gradient in regional elevation, temperature, and precipitation to allow evaluation of consistency in local versus regional variation. We converted foliar loss via BIH to fluxes of C, nitrogen (N), and phosphorus (P) from the birch canopy to the soil to compare with other relevant soil inputs of the same elements and assessed different abiotic and biotic drivers of the observed variability. We found that leaf area loss due to BIH was similar to 1.6% on average. This is comparable to estimates from tundra, but considerably lower than ecosystems at lower latitudes. The C, N, and P fluxes from canopy to soil associated with BIH were 1-2 orders of magnitude lower than the soil input from senesced litter and external nutrient sources such as biological N fixation, atmospheric deposition of N, and P weathering estimated from the literature. Despite the minor contribution to overall elemental cycling in subarctic birch forests, the higher quality and earlier timing of the input of herbivore deposits to soils compared to senesced litter may make this contribution disproportionally important for various ecosystem functions. BIH increased significantly with leaf N content as well as local elevation along each transect, yet showed no significant relationship with temperature or humidity, nor the commonly used temperature proxy, absolute elevation. The lack of consistency between the local and regional elevational trends calls for caution when using elevation gradients as climate proxies.
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| 5. |
- Lett, Signe, et al.
(författare)
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Seasonal variation in nitrogen fixation and effects of climate change in a subarctic heath
- 2014
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Ingår i: Plant and Soil. - : Springer Science and Business Media LLC. - 0032-079X .- 1573-5036. ; 379:1-2, s. 193-204
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Tidskriftsartikel (refereegranskat)abstract
- Nitrogen fixation associated with cryptogams is potentially very important in arctic and subarctic terrestrial ecosystems, as it is a source of new nitrogen (N) into these highly N limited systems. Moss-, lichen- and legume-associated N-2 fixation was studied with high frequency (every second week) during spring, summer, autumn and early winter to uncover the seasonal variation in input of atmospheric N-2 to a subarctic heath with an altered climate. We estimated N-2 fixation from ethylene production by acetylene reduction assay in situ in a field experiment with the treatments: long- vs. short-term summer warming using plastic tents and litter addition (simulating expansion of the birch forest). N-2 fixation activity was measured from late April to mid November and 33 % of all N-2 was fixed outside the vascular plant growing season (Jun-Aug). This substantial amount underlines the importance of N-2 fixation in the cold period. Warming increased N-2 fixation two- to fivefold during late spring. However, long-term summer warming tended to decrease N-2 fixation outside the treatment (tents present) period. Litter alone did not alter N-2 fixation but in combination with warming N-2 fixation increased, probably because N-2 fixation became phosphorus limited under higher temperatures, which was alleviated by the P supply from the litter. In subarctic heath, the current N-2 fixation period extends far beyond the vascular plant growing season. Climate warming and indirect effects such as vegetation changes affect the process of N-2 fixation in different directions and thereby complicate predictions of future N cycling.
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