| 1. |
- Barthelemy, Hélène, et al.
(författare)
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Short- and long-term plant and microbial uptake of 15N-labelled urea in a mesic tundra heath, West Greenland
- 2024
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Ingår i: Polar Biology. - : Springer Nature. - 0722-4060 .- 1432-2056. ; 47:1, s. 1-15
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Tidskriftsartikel (refereegranskat)abstract
- Terrestrial animals are key elements in the cycling of elements in the Arctic where nutrient availability is low. Waste production by herbivores, in particular urine deposition, has a crucial role for nitrogen (N) recycling, still, it remains largely unexplored. Also, experimental evidence is biased toward short-term studies and Arctic regions under high herbivore pressure. In this study, we aimed to examine the fate of N derived from urine in a nutrient poor tundra heath in West Greenland, with historical low level of herbivory. We performed a pulse labelling with 15N-urea over the plant canopy and explored ecosystem N partition and retention in the short-term (2 weeks and 1 year) and longer-term (5 years). We found that all vascular plants, irrespective of their traits, could rapidly take up N-urea, but mosses and lichens were even more efficient. Total 15N enrichment was severely reduced for all plants 5 years after tracer addition, with the exception of cryptogams, indicating that non-vascular plants constituted a long-term sink of 15N-urea. The 15N recovery was also high in the litter suggesting high N immobilization in this layer, potentially delaying the nutrients from urine entering the soil compartment. Long-term 15N recovery in soil microbial biomass was minimal, but as much as 30% of added 15N remained in the non-microbial fraction after 5 years. Our results demonstrate that tundra plants that have evolved under low herbivory pressure are well adapted to quickly take advantage of labile urea, with urine having only a transient effect on soil nutrient availability.
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| 2. |
- Egelkraut, Dagmar, 1989-, et al.
(författare)
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Reindeer trampling promotes vegetation changes in tundra heathlands : Results from a simulation experiment
- 2020
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Ingår i: Journal of Vegetation Science. - : John Wiley & Sons. - 1100-9233 .- 1654-1103. ; 31:3, s. 476-486
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Tidskriftsartikel (refereegranskat)abstract
- Question: Herbivores exert strong influences on vegetation through activities such as trampling, defoliation, and fertilization. The combined effect of these activities on plant performance may cause dramatic vegetation shifts. Because herbivore pressures and the relative importance of their different activities are not equally distributed across the landscape, it is important to understand their isolated effect. One example of an herbivore‐induced vegetation shift is the reindeer‐driven transition from a subarctic tundra vegetation dominated by dwarf shrubs into a more productive, graminoid‐dominated state. Here, we asked how each of the grazing activities by reindeer separately and combined shape vegetation composition.Location: Nordreisa, Norway.Methods: We used a field experiment over six summers to study the separate and interacting effects of reindeer trampling, defoliation, addition of faeces and removal of moss on tundra heath vegetation, and to identify which of these factors were most important in driving the plant community towards a graminoid‐dominated state.Results: The combination of all treatments resulted in the strongest changes in vegetation, but trampling was the single most important factor altering the vegetation composition by reducing the abundance of both evergreen and deciduous dwarf shrubs. In contrast to what was expected, none of our treatments, separate or combined, resulted in an increased abundance of graminoids in 5 years, although such rapid vegetation changes have been observed in the field in similar environmental conditions.Conclusions: Trampling is the key process by which reindeer influence the abundance of functional groups, but only many processes combined result in strong changes in community composition. Moreover, additional factors not included in this experiment, such as urine, may be important in causing a state shift to a graminoid‐dominated community.
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