Journal
SOIL BIOLOGY & BIOCHEMISTRY
Volume 69, Issue -, Pages 413-420Publisher
PERGAMON-ELSEVIER SCIENCE LTD
DOI: 10.1016/j.soilbio.2013.11.015
Keywords
Nitrogen fixation; Acetylene reduction assay; N-15 method; Alternative nitrogenase; Molybdenum; Vanadium
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Funding
- NSF [EAR 1024553]
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The relative contributions of the alternative (V- and Fe-only) and canonical (Mo-) nitrogenases to N-2 fixation in natural environments are still largely unknown. Here we combine chemical and molecular approaches to examine their role in terrestrial ecosystems. Pure-culture studies show that while the R ratio (defined as R = acetylene reduction rate/N-2 fixation rate by nitrogenase) is highly variable, low R ratios (0.5 < R < 2) are usually an indication of alternative nitrogenase activity. Microcosm experiments with temperate soils showed low R ratios and a large increase in N-2 fixation rates in response to vanadium amendments, indicating V-nitrogenase activity. Using RT-PCR, we were able to demonstrate expression of the V-nitrogenase, together with the Mo-nitrogenase, in these soils. An analysis of published R ratios showed that the contribution of alternative nitrogenases to asymbiotic N-2 fixation in soils may be more prevalent than previously recognized. (C) 2013 Elsevier Ltd. All rights reserved.
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