A comprehensive survey of archaeal and bacterial communities in 146 soils worldwide revealed that archaea, primarily Crenarchaeota, are common in soil, but their structure and factors regulating diversity and abundance remain poorly understood. Barcoded pyrosequencing identified two dominant archaeal phylotypes within the Crenarchaeota, accounting for over 70% of all archaeal sequences. These phylotypes were closely related to a previously identified putative ammonia oxidizer, but their abundance decreased with increasing nitrogen availability, suggesting competitive interactions with nitrifying bacteria. Soil C:N ratio was the only consistently correlated factor with archaeal abundance, being higher in soils with lower C:N ratios. The study highlights the importance of examining a broad range of soils to understand the ecological roles of archaea. The findings suggest that archaea inhabit a more restricted ecological niche in soils compared to bacteria, and that dominant archaeal populations may be influenced by environmental factors such as nitrogen availability. The study also underscores the need for further research to fully understand the functional roles of these archaea in soil ecosystems.A comprehensive survey of archaeal and bacterial communities in 146 soils worldwide revealed that archaea, primarily Crenarchaeota, are common in soil, but their structure and factors regulating diversity and abundance remain poorly understood. Barcoded pyrosequencing identified two dominant archaeal phylotypes within the Crenarchaeota, accounting for over 70% of all archaeal sequences. These phylotypes were closely related to a previously identified putative ammonia oxidizer, but their abundance decreased with increasing nitrogen availability, suggesting competitive interactions with nitrifying bacteria. Soil C:N ratio was the only consistently correlated factor with archaeal abundance, being higher in soils with lower C:N ratios. The study highlights the importance of examining a broad range of soils to understand the ecological roles of archaea. The findings suggest that archaea inhabit a more restricted ecological niche in soils compared to bacteria, and that dominant archaeal populations may be influenced by environmental factors such as nitrogen availability. The study also underscores the need for further research to fully understand the functional roles of these archaea in soil ecosystems.