Biogeography of soil Thaumarchaeota in relation to soil depth and land usage

Although Thaumarchaeota are important contributors to ammonia oxidation in terrestrial habitats, distributions of ammonia oxidizers along soil depth profiles are poorly understood, especially in relation to distinct land usages. Leveraging the close proximity of forest, field and agricultural plots at the RARE: Charitable Research Reserve, we examined soil thaumarchaeotal biogeography at three different depths (0-15, 15-30 and 30-45 cm) from plots within areas of contrasting land usage. Data from high-throughput sequencing of thaumarchaeotal 16S rRNA gene sequences demonstrated that OTU richness was affected significantly by depth and land-use type. Specifically, thaumarchaeotal diversity was higher in soils from forest sites than from field sites, and lower within 0-15 cm soils than either 15-30 cm or 30-45 cm soils. Soil land-use type influenced the relative abundance of the Soil Crenarchaeota Group (SCG), with a lower relative abundance of SCG in forest sites compared to field sites. At the OTU level, thaumarchaeotal communities changed with increasing soil depth for agricultural soils, in contrast to homogeneous depth profiles generated from forest site samples. Soil pH was the strongest factor impacting thaumarchaeotal community composition and, importantly, the evenness of archaeal taxa. Nitrogen, carbon and soil texture shaped thaumarchaeotal community composition among field site samples.