Elevational Patterns in Archaeal Diversity on Mt.Fuji

Little is known of how archaeal diversity and community ecology behaves along elevational gradients. We chose to study Mount Fuji of Japan as a geologically and topographically uniform mountain system, with a wide range of elevational zones. Surface soil samples were taken at 500m elevational intervals, between the base of the mountain at 1,000 m and its summit at 3,700 m. PCR-amplified soil DNA for the archaeal 16S gene targeting the V1–V3 region was pyrosequenced, and taxonomically classified against three different archaeal databases (EzTaxon, RDP and SILVA). At a cut-off of 80%, most of the archaeal sequences were classified into phylum Thaumarchaeota (96%) and Euryarchaeota (3.9%), with no sequences classified into phyla Crenarchaeota, Korarchaeota or Nanoarchaeota. Archaeal OTU richness and diversity on Fuji showed a pronounced 'bulge' in the mid-elevations, around 1500m, within the boreal forest zone, compared to the temperate forest zone below and the alpine fellfield and desert zones above. This parallels the trend seen in bacteria in the same samples, although the maximum diversity for bacteria was at somewhat higher elevations. Each elevational sampling zone showed a distinct archaeal community, revealed by ordination clustering, suggesting that many archaeal 'species' have quite finely adjusted niches. The main phylum of archaea found here, Thaumarchaeota, shows the same elevational trend as archaea in general. Diversity decreased towards higher elevations but was finally accompanied by a subtle increase at the summit, mainly due to an increase in the abundance of the group I.1b of Thaumarchaeota. Archaeal diversity shows a strong positive correlation with soil NH4, K and NO3, although it is unclear whether these or some other factor is the major cause of the trend. It is unclear from this exploratory study what the causal factors behind the mid-elevation diversity bulge of archaea might be. Archaeal diversity does not parallel plant diversity, which declines with increasing elevation, although it does roughly parallel bacterial diversity. It is unclear whether both prokaryote groups are responding to the same types of factors. There is clearly a need for further observational and experimental studies to explore the causal factors behind archaeal diversity and community composition in soils.