Abstract
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. PCR-amplified soil DNA for the archaeal 16 S rRNA gene was pyrosequenced and taxonomically classified against EzTaxon-e archaeal database. At a bootstrap cut-off of 80%, most of the archaeal sequences were classified into phylum Thaumarchaeota (96%) and Euryarchaeota (3.9%), with no sequences classified into other phyla. Archaeal OTU richness and diversity on Fuji showed a pronounced ‘peak’ in the mid-elevations, around 1500 masl, within the boreal forest zone, compared to the temperate forest zone below and the alpine fell-field and desert zones above. Diversity decreased towards higher elevations followed by a subtle increase at the summit, mainly due to an increase in the relative abundance of the group I.1b of Thaumarchaeota. Archaeal diversity showed a strong positive correlation with soil NH4 +, K and NO3 − . Archaeal diversity does not parallel plant diversity, although it does roughly parallel bacterial diversity. Ecological hypotheses to explain the mid diversity bulge on Fuji include intermediate disturbance effects, and the result of mid elevations combining a mosaic of upper and lower slope environments. Our findings show clearly that archaeal soil communities are highly responsive to soil environmental gradients, in terms of both their diversity and community composition. Distinct communities of archaea specific to each elevational zone suggest that many archaea may be quite finely niche-adapted within the range of soil environments. A further interesting finding is the presence of a mesophilic component of archaea at high altitudes on a mountain that is not volcanically active. This emphasizes the importance of microclimate – in this case solar heating of the black volcanic ash surface – for the ecology of soil archaea.
Highlights
In the three decades since the discovery of archaea [1] and the two decades since its formal recognition as a new domain of life [2], our understanding of archaeal biology, ecology and evolution has expanded considerably
While archaea were at first regarded as life forms confined to the extremophilic environments, based on the characterization of cultivated specimens found in such environments [2,3], they have been found in a wide variety of habitats both exotic and mundane, including hydrothermal vents, [4], marine waters, [5,6], marine sediments [7,8,9], freshwater sediments, [10,11,12,13], soil [14,15,16,17,18], subsurface goldmine [19], the hindgut of termites [20] and the casts of earthworms [21], thereby breaking the ‘extremophilic stereotype’ [22]
Thaumarchaeota - initially classified as mesophilic crenarchaeota - are amongst the most abundant archaea on Earth, found in a wide variety of ecosystems including soils, marine and fresh waters as well as in moderately extremophilic environments
Summary
In the three decades since the discovery of archaea [1] and the two decades since its formal recognition as a new domain of life [2], our understanding of archaeal biology, ecology and evolution has expanded considerably. Even though over a hundred archaeal genome sequences are publicly available [24] and our knowledge of the archaea has increased substantially but still our understanding of its diversity and community ecology is limited. Bates et al [26] sought the environmental factors which regulate the diversity and abundance of archaeal communities in soil with 146 samples from the Americas and Antarctica. These two major studies and other recent investigations suggest that archaeal communities can be influenced by salinity and pH, [25,27], elevation, [28], climate and vegetation cover [29] or C/N ratio [26]. This study showed that the abundance of ammonia oxidizing archaea (AOA) was negatively correlated with altitude
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