| 1. |
- Ackermann, Kathrin, et al.
(författare)
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N-2 Fixation in Feather Mosses is a Sensitive Indicator of N Deposition in Boreal Forests
- 2012
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Ingår i: Ecosystems. - : Springer Science and Business Media LLC. - 1432-9840 .- 1435-0629. ; 15:6, s. 986-998
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Tidskriftsartikel (refereegranskat)abstract
- Nitrogen (N) fixation in the feather moss-cyanobacteria association represents a major N source in boreal forests which experience low levels of N deposition; however, little is known about the effects of anthropogenic N inputs on the rate of fixation of atmospheric N-2 in mosses and the succeeding effects on soil nutrient concentrations and microbial community composition. We collected soil samples and moss shoots of Pleurozium schreberi at six distances along busy and remote roads in northern Sweden to assess the influence of road-derived N inputs on N-2 fixation in moss, soil nutrient concentrations and microbial communities. Soil nutrients were similar between busy and remote roads; N-2 fixation was higher in mosses along the remote roads than along the busy roads and increased with increasing distance from busy roads up to rates of N-2 fixation similar to remote roads. Throughfall N was higher in sites adjacent to the busy roads but showed no distance effect. Soil microbial phospholipid fatty acid (PLFA) composition exhibited a weak pattern regarding road type. Concentrations of bacterial and total PLFAs decreased with increasing distance from busy roads, whereas fungal PLFAs showed no distance effect. Our results show that N-2 fixation in feather mosses is highly affected by N deposition, here derived from roads in northern Sweden. Moreover, as other measured factors showed only weak differences between the road types, atmospheric N-2 fixation in feather mosses represents a highly sensitive indicator for increased N loads to natural systems.
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| 2. |
- Hicks, Lettice C., et al.
(författare)
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Soil Microbial Responses to 28 Years of Nutrient Fertilization in a Subarctic Heath
- 2020
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Ingår i: Ecosystems. - : Springer Science and Business Media LLC. - 1432-9840 .- 1435-0629. ; 23:5, s. 1107-1119
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Tidskriftsartikel (refereegranskat)abstract
- Arctic and subarctic soils are typically characterized by low nitrogen (N) availability, suggesting N-limitation of plants and soil microorganisms. Climate warming will stimulate the decomposition of organic matter, resulting in an increase in soil nutrient availability. However, it remains unclear how soil microorganisms in N-limited soils will respond, as the direct effect of inorganic N addition is often shown to inhibit microbial activity, while elevated N availability may have a positive effect on microorganisms indirectly, due to a stimulation of plant productivity. Here we used soils from a long-term fertilization experiment in the Subarctic (28 years at the time of sampling) to investigate the net effects of chronic N-fertilization (100 kg N ha−1 y−1, added together with 26 kg P and 90 kg K ha−1 y−1, as expected secondary limiting nutrients for plants) on microbial growth, soil C and N mineralization, microbial biomass, and community structure. Despite high levels of long-term fertilization, which significantly increased primary production, we observed relatively minor effects on soil microbial activity. Bacterial growth exhibited the most pronounced response to long-term fertilization, with higher rates of growth in fertilized soils, whereas fungal growth remained unaffected. Rates of basal soil C and N mineralization were only marginally higher in fertilized soils, whereas fertilization had no significant effect on microbial biomass or microbial community structure. Overall, these findings suggest that microbial responses to long-term fertilization in these subarctic tundra soils were driven by an increased flow of labile plant-derived C due to stimulated plant productivity, rather than by direct fertilization effects on the microbial community or changes in soil physiochemistry.
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| 3. |
- Hicks, Lettice
(författare)
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Increased Above- and Belowground Plant Input Can Both Trigger Microbial Nitrogen Mining in Subarctic Tundra Soils
- 2022
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Ingår i: Ecosystems. - : Springer Science and Business Media LLC. - 1432-9840 .- 1435-0629. ; 25:1, s. 105-121
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Tidskriftsartikel (refereegranskat)abstract
- Low nitrogen (N) availability in the Arctic and Subarctic constrains plant productivity, resulting in low litter inputs to soil. Increased N availability and litter inputs as a result of climate change, therefore, have the potential to impact the functioning of these ecosystems. We examined plant and microbial responses to chronic inorganic N (5 g m−2 year−1) and/or litter (90 g m−2 year−1), supplied during three growing seasons. We also compared the response to more extreme additions, where the total cumulative additions of N (that is, 15 g m−2) and litter (that is, 270 g m−2) were concentrated into a single growth season. Plant productivity was stimulated by N additions and was higher in the extreme addition plots than those with chronic annual additions. Microbial community structure also differed between the chronic and extreme plots, and there was a significant relationship between plant and microbial community structures. Despite differences in microbial structure, the field treatments had no effect on microbial growth or soil C mineralization. However, gross N mineralization was higher in the N addition plots. This led to a lower ratio of soil C mineralization to gross N mineralization, indicating microbial targeting of N-rich organic matter (“microbial N-mining”), likely driven by the increased belowground C-inputs due to stimulated plant productivity. Surprisingly, aboveground litter addition also decreased ratio of soil C mineralization to gross N mineralization. Together, these results suggest that elevated N availability will induce strong responses in tundra ecosystems by promoting plant productivity, driving changes in above- and belowground community structures, and accelerating gross N mineralization. In contrast, increased litter inputs will have subtle effects, primarily altering the ratio between C and N derived from soil organic matter.
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