During the last decade it has been discovered that around 2% of the soil-living prokaryotes belong to the domain Archaea. In many soils the most abundant archaeal group is the ammonia-oxidizing archaea (AOA) that, in addition to ammonia-oxidizing bacteria (AOB), preform the first and rate-limiting step in the nitrification process. The knowledge of factors that regulates the archaeal abundance and activity, and their importance in the carbon and nitrogen turnover in soil, is very limited. The aim of this thesis was to investigate how archaeal abundance and activity is influenced by carbon, pH and nitrogen amendments, and in the long run increase the knowledge of the role of soil-living archaea in carbon and nitrogen turnover.
Soil pH was shown to be an important factor determining the archaeal 16S rRNA gene abundance. The lowest abundance was found at pH 5.1 and increased 150-fold with increasing pH (up to 8.3). In the low pH range (4.0-4.7), no correlation with pH was found.