Biogeography of soil thaumarchaeota along soil depth in Ontario, Canada

Although thaumarchaeota are important contributors to ammonia oxidation in terrestrial habitats, distributions of ammonia oxidizers and the mechanisms shaping their community composition along soil depth profiles are poorly understood, especially as these relate to distinct land usages. Focusing on the unique distribution of forest, field, and agricultural plots available at the rare Charitable Research Reserve (Cambridge, Ontario), we compared soil thaumarchaeotal distributions at three different depths (0-15 cm, 15-30 cm and 30-45 cm) from within contrasting land usages. Using high-throughput sequencing of thaumarchaeal 16S rRNA gene sequences, we identified that OTU richness was significantly affected by land-use type and depth. Specifically, thaumarchaeal diversity was higher in soil samples from forest sites than from field sites, and lower within 0-15 cm soils than either 15-30 cm or 30-45 cm soils. Although the Soil Crenarchaeota Group (SCG) dominated all samples, a lower relative abundance of SCG was observed in forest sites comparing to field sites. At the OTU level, community composition separation along soil depth was shown in field sites, but not forest sites. Importantly, pH was the environmental variable that differentiated thaumarchaeotal community composition at field sites from forest sites, and nitrogen, carbon, and soil texture shaped thaumarchaeotal community composition among field sites.