title: Non-cyanobacterial diazotrophs mediate dinitrogen fixation in biological soil crusts during early crust formation.
abstract: Biological soil crusts (BSCs) are key components of ecosystem productivity in arid lands and they cover a substantial fraction of the terrestrial surface. In particular, BSC N2-fixation contributes significantly to the nitrogen (N) budget of arid land ecosystems. In mature crusts, N2-fixation is largely attributed to heterocystous cyanobacteria; however, early successional crusts possess few N2-fixing cyanobacteria and this suggests that microorganisms other than cyanobacteria mediate N2-fixation during the critical early stages of BSC development. DNA stable isotope probing with (15)N2 revealed that Clostridiaceae and Proteobacteria are the most common microorganisms that assimilate (15)N2 in early successional crusts. The Clostridiaceae identified are divergent from previously characterized isolates, though N2-fixation has previously been observed in this family. The Proteobacteria identified share >98.5% small subunit rRNA gene sequence identity with isolates from genera known to possess diazotrophs (for example, Pseudomonas, Klebsiella, Shigella and Ideonella). The low abundance of these heterotrophic diazotrophs in BSCs may explain why they have not been characterized previously. Diazotrophs have a critical role in BSC formation and characterization of these organisms represents a crucial step towards understanding how anthropogenic change will affect the formation and ecological function of BSCs in arid ecosystems.
authors.affiliation: Department of Crop and Soil Sciences, School of Integrative Plant Sciences, Cornell University, Ithaca, NY, USA.
authors.forename: Charles
authors.initials: C
authors.lastname: Pepe-Ranney
authors.affiliation: Department of Microbiology, Cornell University, Ithaca, NY, USA.
authors.forename: Chantal
authors.initials: C
authors.lastname: Koechli
authors.affiliation: School of Life Sciences, Arizona State University, Tempe, AZ, USA.
authors.forename: Ruth
authors.initials: R
authors.lastname: Potrafka
authors.affiliation: Department of Microbiology, Cornell University, Ithaca, NY, USA.
authors.forename: Cheryl
authors.initials: C
authors.lastname: Andam
authors.affiliation: Department of Microbiology, Cornell University, Ithaca, NY, USA.
authors.forename: Erin
authors.initials: E
authors.lastname: Eggleston
authors.affiliation: School of Life Sciences, Arizona State University, Tempe, AZ, USA.
authors.forename: Ferran
authors.initials: F
authors.lastname: Garcia-Pichel
authors.affiliation: Department of Crop and Soil Sciences, School of Integrative Plant Sciences, Cornell University, Ithaca, NY, USA.
authors.forename: Daniel H
authors.initials: DH
authors.lastname: Buckley
mesh_terms: D052818:Autotrophic Processes; D001419:Bacteria / Q000145:classification / Q000235:genetics / Q000302:isolation & purification* / Q000378:metabolism*; D017753:Ecosystem; D019015:Geologic Sediments / Q000382:microbiology*; D052836:Heterotrophic Processes; D008969:Molecular Sequence Data; D009584:Nitrogen / Q000378:metabolism; D009586:Nitrogen Fixation; D010802:Phylogeny; D012988:Soil Microbiology
chemical_list: D009584:Nitrogen