Nitrogen fixation in Arctic vegetation and soils from Svalbard,Norway |
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Authors: | B Solheim A Endal H Vigstad |
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Institution: | 1. Institute of Biology and Geology, University of Troms?, N-9037, Troms?, Norway
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Abstract: | Nitrogen fixation was measured by the acetylene reduction method in a high Arctic ecosystem at Kongsfjorden, Spitsbergen (79°N,
12°E). The most important source of biologically fixed nitrogen was found in cyanobacteria either as free living colonies
ofNostoc sp. in wet unvegetated or sparsely vegetated grounds or growing as epiphytes on bryophytes. Fixation associated with plant
roots or in soil and peat samples had little or no significance for nitrogen input to the ecosystem. The ability to support
an epiphytic flora of nitrogen-fixing cyanobacteria varied greatly between bryophyte species.Calliergon richardsonii andSanionia uncinata seemed especially well adapted for harbouring epiphytic cyanobacteria, but the extent of nitrogen fixation varied with the
growing location. The rate of nitrogen fixation was greatly influenced by grazing by geese. In a geese-grazing area values
were found with a maximum of 693.6±1.5 nmol C2H4 h−1 g (dry weight)−1 while the maximum value for ungrazed areas was 65.3±16.6 nmol C2H4 h−1 g (dry weight)−1. In the grazed area cyanobacteria were also found fixing nitrogen epiphytically on grass. The high plant productivity, supporting
heavy grazing, clearly indicates an effective transfer of fixed nitrogen to the plant community. Under cliffs harbouring colonies
of birds, the biological nitrogen fixation was inhibited by bird droppings. |
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