The influence of abiotic factors on biological nitrogen fixation in different types of vegetation in the High Arctic, Svalbard

The influence of environmental factors on the nitrogen fixation activity in soil and vegetation samples from different types of plant communities from the Sassen Valley (78degreesN, 16degreesE), Svalbard, Norway, was measured under controlled laboratory conditions using the Acetylene reduction assay throughout the summers of 1997 and 2000. Samples for study were chosen from six sites along a 2-km-long transect representing different types of arctic vegetation. The influence of temperature soil water content, and light intensity on acetylene reduction rates was studied. Samples from all site; showed low and almost constant acetylene reduction rates between 0 and 10degreesC. Above 10degreesC the activity of all samples increased rapidly and reached its maximum at about 25 and 32degreesC for the samples with free-living cyanobacteria and moss-associated cyanobacteria, respectively. There was a significant water-dependent increase of acetylene reduction activity for all types of vegetation. The samples showed a clear response to varying light conditions, i.e. a rapid decrease in acetylene reduction rates when light intensity decreased from 140 to 80 mumol m(-2) s(-1) depending on the type of vegetation.