title: Associative nitrogen fixation in nodules of the conifer Lepidothamnus fonkii (Podocarpaceae) inhabiting ombrotrophic bogs in southern Patagonia.
abstract: Biological N2fixation (BNF) in the rhizosphere of Podocarpaceae is currently attributed to unspecific diazotrophs with negligible impact on N acquisition. Here, we report specific and high associative BNF in dead cells of root nodules of Lepidothamnus fonkii distributed in ombrotrophic peatlands of Patagonia. BNF of nodulated roots, intact plants of L. fonkii and rhizospheric peat was assessed by15N2and acetylene reduction. Diazotrophs were identified by electron microscopy, analysis of nitrogenase encoding genes (nifH) and transcripts, and 16S rRNA. Nitrogenase encoding nifH transcripts from root nodules point to Beijerinckiaceae (Rhizobiales), known as free-living diazotrophs. Electron microscopy and 16S rRNA analysis likewise identified active Beijerinckiaceae in outer dead cells of root nodules. NifH transcripts from the rhizopshere peat revealed diverse active diazotrophs including Beijerinckiaceae. Both methods revealed high activity of nitrogenase rates in cut roots of L. fonkii (2.5 μmol N g-1d.w. d-1based on15N2assay; 2.4 μmol C2H4g-1d.w. d-1based on acetylene reduction assay). The data suggest that (i) nodules recruit diazotrophic Beijerinckiaceae from peat, (ii) dead nodule cells provide an exclusive habitat for Beijerinckiaceae, and (iii) BNF in L. fonkii is one potent pathway to overcome N deficiency in ombrotrophic peatlands of Patagonia.
authors.affiliation: University of Bayreuth, Department of Soil Ecology, Dr.-Hans-Frisch-Str. 1-3, 95448 Bayreuth, Germany.
authors.forename: Werner
authors.initials: W
authors.lastname: Borken
authors.affiliation: University of Bayreuth, Ecological Microbiology, Dr.-Hans-Frisch-Str. 1-3, 95448 Bayreuth, Germany.|University of Hannover, Institute of Microbiology, Herrenhäuserstr. 2, 30140 Hannover, Germany.
authors.forename: Marcus A
authors.initials: MA
authors.lastname: Horn
authors.affiliation: University of Bayreuth, Cell Biology and Electron Microscopy, Universitätsstr, 30, 95440 Bayreuth, Germany.
authors.forename: Stefan
authors.initials: S
authors.lastname: Geimer
authors.affiliation: Universidad de Magellanes, Instituto de la Patagonia, Laboratorio de Botanica, Av. Manuel Bulnes 01890, Punta Arenas, Chile.|ONG AMA Torres del Paine, Estancia Cerro Paine S/N, Torres del Payne, Chile.
authors.forename: Nelson A Bahamonde
authors.initials: NA
authors.lastname: Aguilar
authors.affiliation: University of Münster, ILÖK, Hydrology group, Heisenbergstr, 2, 48149, Münster, Germany.
authors.forename: Klaus-Holger
authors.initials: KH
authors.lastname: Knorr
mesh_terms: D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism; D017753:Ecosystem; D008854:Microscopy, Electron; D009584:Nitrogen / Q000032:analysis*; D009586:Nitrogen Fixation; D009591:Nitrogenase / Q000235:genetics / Q000378:metabolism; D010802:Phylogeny; D012336:RNA, Ribosomal, 16S / Q000235:genetics; D012230:Rhizobiaceae / Q000145:classification / Q000235:genetics / Q000302:isolation & purification*; D053204:Root Nodules, Plant / Q000737:chemistry* / Q000382:microbiology; D012988:Soil Microbiology; D064028:Tracheophyta / Q000254:growth & development* / Q000382:microbiology
chemical_list: D001426:Bacterial Proteins; D012336:RNA, Ribosomal, 16S; D009591:Nitrogenase; D009584:Nitrogen