Plant and Soil

, Volume 379, Issue 1–2, pp 193–204 | Cite as

Seasonal variation in nitrogen fixation and effects of climate change in a subarctic heath

  • Signe Lett
  • Anders Michelsen
Regular Article


Background and aims

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 N2 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 N2 to a subarctic heath with an altered climate.


We estimated N2 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).


N2 fixation activity was measured from late April to mid November and 33 % of all N2 was fixed outside the vascular plant growing season (Jun–Aug). This substantial amount underlines the importance of N2 fixation in the cold period. Warming increased N2 fixation two- to fivefold during late spring. However, long-term summer warming tended to decrease N2 fixation outside the treatment (tents present) period. Litter alone did not alter N2 fixation but in combination with warming N2 fixation increased, probably because N2 fixation became phosphorus limited under higher temperatures, which was alleviated by the P supply from the litter.


In subarctic heath, the current N2 fixation period extends far beyond the vascular plant growing season. Climate warming and indirect effects such as vegetation changes affect the process of N2 fixation in different directions and thereby complicate predictions of future N cycling.


Bryophytes Global change Lichens Litter addition Long- vs. short-term warming Nitrogen and phosphorus Plant cover 



We thank Gosha Sylvester for laboratory assistance with chemical analyses at the University of Copenhagen, ANS for providing facilities for laboratory analyses and fieldwork, and Ida Vedel-Petersen for carrying out ARA in June and July 2011. We gratefully acknowledge financial support from “Docent, Dr. Scient. Lauritz W. Olsons rejsefond”, the Danish Council for Independent Research, and from the Danish National Research Foundation (CENPERM DNRF100). Also, we thank the anonymous reviewers and the subject editor for their highly valuable comments and suggestions.

Supplementary material

11104_2014_2031_Fig4_ESM.jpg (295 kb)

Mean water content (Vol. %) in treatment plots on each measurement day; C, control; W, long-term warming; L, litter; WL; combined warming and litter; Wshort, short-term warming. Shading marks presence of tents. Water saturated soil gives a value of 0.56. Bars are data means +SE, n = 6. Comparison of short- vs. long-term warming using C, W and Wshort were done with one-way ANOVA (Treatment as factor): Treat: NS, Time P < 0.0001, Moss cover P < 0.05, Treat*Time P < 0.0001. Comparison of effects of litter addition and long-term warming using C, L, W and WL were done with two-way ANOVA (Litter and Warming as factors): Warming: NS, Litter: P < 0.05, Time P < 0.0001, Moss cover P < 0.05, Litter*Time P < 0.0001. Dates with no data (ND) were due to frozen soil (JPEG 295 kb)

11104_2014_2031_MOESM1_ESM.eps (1.1 mb)
High Resolution Image (EPS 1094 kb)


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Copyright information

© Springer International Publishing Switzerland 2014

Authors and Affiliations

  1. 1.Department of Biology, Terrestrial Ecology SectionUniversity of CopenhagenCopenhagenDenmark
  2. 2.Climate Impacts Research Centre, Department of Ecology and Environmental ScienceUmeå UniversityAbiskoSweden
  3. 3.Center for Permafrost (CENPERM)University of CopenhagenCopenhagenDenmark

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