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

• Published in: Plant and soil Vol. 379; no. 1/2; pp. 193 - 204
• Main Authors: Lett, Signe, Michelsen, Anders
• Format: Journal Article
• Language: English
• Published: Cham Springer 01.06.2014; Springer International Publishing; Springer Nature B.V
• Subjects: Acetylene reduction; Agronomy. Soil science and plant productions; Animal, plant and microbial ecology; Arctic regions; autumn; Betula; Biogeochemistry; Biological and medical sciences; Biomedical and Life Sciences; Botanical research; Botany; Bryophytes; climate; Climate change; Climate effects; Climatic changes; Cryptogams; Ecology; Environmental aspects; Ethylene production; field experimentation; Fixation; Forest soils; forests; Fundamental and applied biological sciences. Psychology; General agronomy. Plant production; Global change; Global warming; Growing season; Growing seasons; High temperature; Lichens; Life Sciences; Litter; Litter addition; Long-vs. short-term warming; Nitrogen; Nitrogen and phosphorus; Nitrogen fixation; phosphorus; Plant cover; Plant Physiology; Plant Sciences; Plants; Regular Article; seasonal variation; Seasonal variations; Seasons; Soil heating; Soil Science & Conservation; Soil sciences; Soil-plant relationships. Soil fertility; Soil-plant relationships. Soil fertility. Fertilization. Amendments; Spring; Summer; Taiga & tundra; temperature; Terrestrial ecosystems; Vascular plants; Vegetation; Vegetation changes; winter; Denmark; PN, Arctic; Lichens; Long- vs. short-term warming; Global change; Nitrogen and phosphorus; Plant cover; Litter addition; Bryophytes; Short term; Time variation; Fungi; Seasonal variation; Nitrogen fixation; Warming; Heathland and moor; Vegetals; Addition; Litter; Bryophyta; Phosphorus; Subpolar zone; Nitrogen; Dynamical climatology; Climate change; Lichenes; Soil plant relation
• ISSN: 0032-079X; 1573-5036; 1573-5036
• DOI: 10.1007/s11104-014-2031-y

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. Methods 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). Results 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. Wanning increased N₂ fixation two-to fivefold during late spring. However, longterm 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. Conclusion 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.