The roots of seven species of goldenrod (Asteraceae: Solidago) were assayed for associative nitrogen fixation. We used the acetylene reduction method to measure N2 fixation rates in sampling jars that contained roots of sampled plants and soil. The rate of C2H2 reduction in jars with S. rigida (12.9 ± 1.2 nmol h-1, mean ± SE) and S. canadensis (6.0 ± 2.0 nmol h-1) was significantly higher than in soil-only control jars. There was measurable C2H2 reduction in jars of the other five species, but the rates were not significantly different from controls. The rates of C2H2 reduction per root dry weight and per total plant dry weight also were higher for S. rigida and S. canadensis than for the other species.
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Acknowledgements-We appreciateco mmentso n a draft of this manuscript from C. Cole, E. J. Cushing, D. B. Lawrencea nd P. A. Morrow. This work was supportedb y NSF grant DEB-8114302-A0t2o D. Tilman and J. Tester of the Universityo f Minnesotaf or Long-Term Ecological Researcha t Cedar Creek Natural History Area, and by an Alexandera nd Lydia AndersonF ellowshipt o M.J.M. from the University of MinnesotaG raduateS chool.