Two Decades of Experimental Manipulations of Heaths and Forest Understory in the Subarctic

Michelsen, Anders; Rinnan, Riikka; Jonasson, Sven

doi:10.1007/s13280-012-0303-4

Cited by 47 publications

(48 citation statements)

References 74 publications

(117 reference statements)

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“…During the last two decades, vegetation phenology in the Arctic has been monitored using both in situ field measurements focusing on seasonal dynamics in growth (Ellebjerg et al 2008; Michelsen et al 2012) and its linkage to CO 2 exchange (Kross et al 2014). In parallel, Arctic vegetation has been monitored from satellites (e.g., Zeng et al 2011), allowing for regional-scale studies.…”

Section: Introductionmentioning

confidence: 99%

Transitions in high-Arctic vegetation growth patterns and ecosystem productivity tracked with automated cameras from 2000 to 2013

Westergaard‐Nielsen

Lund

Pedersen

et al. 2017

Ambio

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Climate-induced changes in vegetation phenology at northern latitudes are still poorly understood. Continued monitoring and research are therefore needed to improve the understanding of abiotic drivers. Here we used 14 years of time lapse imagery and climate data from high-Arctic Northeast Greenland to assess the seasonal response of a dwarf shrub heath, grassland, and fen, to inter-annual variation in snow-cover, soil moisture, and air and soil temperatures. A late snow melt and start of growing season is counterbalanced by a fast greenup and a tendency to higher peak greenness values. Snow water equivalents and soil moisture explained up to 77 % of growing season duration and senescence phase, highlighting that water availability is a prominent driver in the heath site, rather than temperatures. We found a significant advance in the start of spring by 10 days and in the end of fall by 11 days, resulting in an unchanged growing season length. Vegetation greenness, derived from the imagery, was correlated to primary productivity, showing that the imagery holds valuable information on vegetation productivity.Electronic supplementary materialThe online version of this article (doi:10.1007/s13280-016-0864-8) contains supplementary material, which is available to authorized users.

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Section: Introductionmentioning

confidence: 99%

Transitions in high-Arctic vegetation growth patterns and ecosystem productivity tracked with automated cameras from 2000 to 2013

Westergaard‐Nielsen

Lund

Pedersen

et al. 2017

Ambio

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“…lichen (<20 %) and mosses (50-100 %) [13][14][15], their input via N 2 fixation at ecosystem level is likely to differ substantially. For instance, although total N 2 fixation rates in some lichens commonly exceed those measured in moss-associated N 2 fixers, N 2 fixation rates converted to area may be magnitudes higher in mosses than in lichens due to high moss ground cover [16][17][18].…”

Section: Introductionmentioning

confidence: 99%

Across-Habitat Comparison of Diazotroph Activity in the Subarctic

et al. 2014

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Nitrogen (N) fixation by N2-fixing bacteria (diazotrophs) is the primary N input to pristine ecosystems like boreal forests and subarctic and arctic tundra. However, the contribution by the various diazotrophs to habitat N2 fixation remains unclear. We present results from in situ assessments of N2 fixation of five diazotroph associations (with a legume, lichen, feather moss, Sphagnum moss and free-living) incorporating the ground cover of the associations in five typical habitats in the subarctic (wet and dry heath, polygon-heath, birch forest, mire). Further, we assessed the importance of soil and air temperature, as well as moisture conditions for N2 fixation. Across the growing season, the legume had the highest total as well as the highest fraction of N2 fixation rates at habitat level in the heaths (>85 % of habitat N2 fixation), whereas the free-living diazotrophs had the highest N2 fixation rates in the polygon heath (56 %), the lichen in the birch forest (87 %) and Sphagnum in the mire (100 %). The feather moss did not contribute more than 15 % to habitat N2 fixation in any of the habitats despite its high ground cover. Moisture content seemed to be a major driver of N2 fixation in the lichen, feather moss and free-living diazotrophs. Our results show that the range of N2 fixers found in pristine habitats contribute differently to habitat N2 fixation and that ground cover of the associates does not necessarily mirror contribution.

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“…The result probably reflects the long-term increase in the total cover of vascular vegetation. After 22 years, both warming and fertilization treatments had 35% higher vascular plant cover than the control [16], in contrast to previous measurements after 5 and 10 years, with varying responses in the two treatments [22]. Increased primary production typically leads to an increase in soil microbial biomass [23], thanks to enhanced substrate inputs.…”

Section: Discussionmentioning

confidence: 99%

Fungi Benefit from Two Decades of Increased Nutrient Availability in Tundra Heath Soil

2013

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If microbial degradation of carbon substrates in arctic soil is stimulated by climatic warming, this would be a significant positive feedback on global change. With data from a climate change experiment in Northern Sweden we show that warming and enhanced soil nutrient availability, which is a predicted long-term consequence of climatic warming and mimicked by fertilization, both increase soil microbial biomass. However, while fertilization increased the relative abundance of fungi, warming caused only a minimal shift in the microbial community composition based on the phospholipid fatty acid (PLFA) and neutral lipid fatty acid (NLFA) profiles. The function of the microbial community was also differently affected, as indicated by stable isotope probing of PLFA and NLFA. We demonstrate that two decades of fertilization have favored fungi relative to bacteria, and increased the turnover of complex organic compounds such as vanillin, while warming has had no such effects. Furthermore, the NLFA-to-PLFA ratio for 13C-incorporation from acetate increased in warmed plots but not in fertilized ones. Thus, fertilization cannot be used as a proxy for effects on warming in arctic tundra soils. Furthermore, the different functional responses suggest that the biomass increase found in both fertilized and warmed plots was mediated via different mechanisms.

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Two Decades of Experimental Manipulations of Heaths and Forest Understory in the Subarctic

Abstract: Current atmospheric warming due to increase of greenhouse gases will have severe consequences for the structure and functioning of arctic ecosystems with chan-

Cited by 47 publications

References 74 publications

Transitions in high-Arctic vegetation growth patterns and ecosystem productivity tracked with automated cameras from 2000 to 2013

Transitions in high-Arctic vegetation growth patterns and ecosystem productivity tracked with automated cameras from 2000 to 2013

Across-Habitat Comparison of Diazotroph Activity in the Subarctic

Fungi Benefit from Two Decades of Increased Nutrient Availability in Tundra Heath Soil

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