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| Titel |
Climatic controls of moss-associated nitrogen fixation in the Subarctic |
| VerfasserIn |
Kathrin Rousk, Anders Michelsen |
| Konferenz |
EGU General Assembly 2017
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 19 (2017) |
| Datensatznummer |
250137458
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| Publikation (Nr.) |
 EGU/EGU2017-176.pdf |
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| Zusammenfassung |
| Nitrogen (N2) fixation performed by moss-associated cyanobacteria is one of the main
sources of new N input in pristine, high latitude ecosystems like boreal forests and subarctic
tundra. However, N2 fixation in mosses is strongly influenced by climatic conditions, in
particular, moisture and temperature. Previous attempts to temporally scaling up
N2 fixation in mosses from low frequency in situ measurements to several weeks,
months or even the entire growing season without taking into account changes in
abiotic conditions could not capture the variation in moss-associated N2 fixation. We
therefore aimed to estimate moss-associated N2 fixation throughout the snow-free
period in subarctic tundra in field experiments simulating climate change: willow
(Salix myrsinifolia) and birch (Betula pubescens spp. tortuosa) litter addition, and
warming. The litter additions were sought to simulate shrub expansion in high latitude
ecosystems. We established relationships between measured in situ N2 fixation rates
and soil moisture and soil temperature and used high-resolution measurements
of soil moisture and soil temperature (hourly from May – October) to model N2
fixation. The modelled N2 fixation rates were highest in the warmed (2.8 ±0.3 kg N
ha−1) and birch litter addition plots (2.8 ±0.2 kg N ha−1), and lowest in the plots
receiving willow litter (1.6 ±0.2 kg N ha−1). The control plots had intermediate rates
(2.2 ±0.2 kg N ha−1). Our findings suggest that a longer snow-free period and
increased temperatures in a future climate will likely lead to higher N2 fixation rates
in mosses. Yet, the consequences of increased litter fall on moss-associated N2
fixation due to shrub expansion in the Arctic will depend on the shrub species’ litter
traits.
To follow up on the strong dependence of moss-associated N2 fixation on moisture and
temperature, we collected mosses along a precipitation gradient in subarctic tundra, Northern
Sweden and exposed the mosses to different temperature and moisture regimes. We compared
N2 fixation in those mosses to test if the positioning along the gradient resulted in differences
in N2 fixation capability. Nitrogen fixation increased with increasing moss-moisture content
and temperature, and the two climatic factors interacted strongly to influence N2 fixation. The
temperature optimum for N2 fixation was 25 ˚ C. Thus, increased temperatures in a
future climate will likely lead to an increased N input via the moss-N2-fixation
pathway if mosses are not outcompeted by shrubs expanding into these ecosystems. |
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