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AME 39:271-279 (2005)
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Abstract
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Diversity and activity of epiphytic nitrogen-fixers on standing dead stems of the salt marsh grass Spartina alterniflora
Pia H. Moisander1,2,*, Michael F. Piehler1,
Hans W. Paerl1
1University of North Carolina at Chapel Hill, Institute of Marine Sciences, 3431 Arendell Street, Morehead City, North Carolina 28557, USA 2Present address: Ocean Sciences Department, University of California Santa Cruz,
1156 High Street, Santa Cruz, California 95064, USA
*Email: pia_moisander@alumni.unc.edu
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ABSTRACT: Microbial communities growing on the surfaces of standing dead stems of salt marsh grasses contribute to fixation of atmospheric nitrogen (N2) in these N-limited intertidal systems. Salt marshes in North Carolina, USA, have been shown
to exhibit N2 fixation throughout the growth season, but the composition of these diazotrophic communities is poorly known. This study investigated the diversity of the epiphytic N2-fixing microbial community on the surfaces of dead
stems (shoots) of the cord grass Spartina alterniflora in a salt marsh in North Carolina. Sequencing of the nifH gene and microscopy showed that a diverse diazotrophic community consisting of at least 8 diazotrophic cyanobacterial
taxa, as well as an assemblage of α-, γ-, and δ-proteobacteria, was present. Half of the recovered unique nifH sequences fell into the cluster with anaerobes. N2-fixation rates under natural irradiance ranged from 0.001
to 2.58 nmol C2H4 µg chl a1 h1 (0.07 to 206 nmol C2H4 cm2 h1) and decreased from spring tofall. Nitrogen-fixation rates had a
positive relationship with chlorophyll a, suggesting phototrophs contributed to N2 fixation. The dominant diazotrophs in this study differed from epiphytic communities described elsewhere in the southeast United States, suggesting
regional differences are present in the diversity of these communities.
KEY WORDS: NifH · Nitrogen fixation · Epiphytes · Salt marsh · Spartina alterniflora · Cyanobacteria · Anaerobes · Diversity
Full text in pdf format
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Published in AME Vol.
39, No. 3
(2005) on June 20
Print ISSN: 0948-3055; Online ISSN: 1616-1564.
Copyright © Inter-Research, Oldendorf/Luhe, 2005
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