Non-cyanobacterial diazotrophs mediate dinitrogen fixation in biological soil crusts during early crust formation.

BioRxiv : the Preprint Server for Biology
Charles Pepe-RanneyDaniel H Buckley


Biological soil crusts (BSC) 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 (DNA-SIP) with 15N2 revealed that Clostridiaceae and Proteobacteria are the most common microorganisms that assimilate 15N2 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% SSU rRNA gene sequence identity with isolates from genera known to possess diazotrophs (e.g. Pseudomonas , Klebsiella , Shigella , and Ideonella ). The low abundance of these heterotrophic diazotrophs in BSC may explain why they have not been characterized previously. Diazotrophs play a critical role in BSC formation an...Continue Reading

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