title: Global biogeography of microbial nitrogen-cycling traits in soil.
abstract: Microorganisms drive much of the Earth's nitrogen (N) cycle, but we still lack a global overview of the abundance and composition of the microorganisms carrying out soil N processes. To address this gap, we characterized the biogeography of microbial N traits, defined as eight N-cycling pathways, using publically available soil metagenomes. The relative frequency of N pathways varied consistently across soils, such that the frequencies of the individual N pathways were positively correlated across the soil samples. Habitat type, soil carbon, and soil N largely explained the total N pathway frequency in a sample. In contrast, we could not identify major drivers of the taxonomic composition of the N functional groups. Further, the dominant genera encoding a pathway were generally similar among habitat types. The soil samples also revealed an unexpectedly high frequency of bacteria carrying the pathways required for dissimilatory nitrate reduction to ammonium, a little-studied N process in soil. Finally, phylogenetic analysis showed that some microbial groups seem to be N-cycling specialists or generalists. For instance, taxa within the Deltaproteobacteria encoded all eight N pathways, whereas those within the Cyanobacteria primarily encoded three pathways. Overall, this trait-based approach provides a baseline for investigating the relationship between microbial diversity and N cycling across global soils.
authors.affiliation: Department of Ecology and Evolutionary Biology, University of California, Irvine, CA 92697;
authors.forename: Michaeline B
authors.initials: MB
authors.lastname: Nelson
authors.affiliation: Department of Ecology and Evolutionary Biology, University of California, Irvine, CA 92697; Department of Earth System Science, University of California, Irvine, CA 92697.
authors.forename: Adam C
authors.identifier: 0000-0003-2829-4314
authors.initials: AC
authors.lastname: Martiny
authors.affiliation: Department of Ecology and Evolutionary Biology, University of California, Irvine, CA 92697; jmartiny@uci.edu.
authors.forename: Jennifer B H
authors.initials: JB
authors.lastname: Martiny
mesh_terms: D001419:Bacteria / Q000145:classification / Q000235:genetics / Q000378:metabolism; D054892:Metagenome; D009584:Nitrogen / Q000378:metabolism; D058458:Nitrogen Cycle; D010802:Phylogeny; D058974:Phylogeography; D012988:Soil Microbiology
chemical_list: D009584:Nitrogen
keywords: ammonia assimilation; dissimilatory nitrite reduction; metagenomics; nitrification; nitrogen fixation