Ecological aspects of nitrogen fixation (acetylene reduction) associated with plants of a Minnesota wetland community

Abstract

Nitrogen fixation in association with four plant species of a Minnesota wetland, Typha latifolia L., Carex stricta Lam., Calamagrostis canadensis (Michx.) Beauv., and Lemna minor L., was estimated using the acetylene-reduction technique on soil – root cores. The estimated rates of nitrogen fixation (acetylene reduction) for plants growing in submerged soils, in kilograms per hectare per year, are T. latifolia, 0.91; Carex stricta, 0.47; Calamagrostis canadensis, 0.24; and L. minor, 1.90. Significantly higher fixation rates were found with plants growing in submerged areas than with those on the well-drained shore. These differences could not be correlated with differences in levels of extractable ammonium and nitrate in the substrate and were attributed to low redox potentials favoring nitrogenase activity in submerged areas. The seasonal trend in acetylene reduction activity appeared to be correlated with the reproductive stages of Typha, Carex, and Calamagrostis. Maximum acetylene reduction for these species was observed just after flower maturation, in early summer for Carex and Calamagrostis and late summer for Typha, suggesting that nitrogen fixation may be an important source of nitrogen in developing seeds. Overall, nitrogen fixation was estimated to supply as much as 11 kg N∙ha−1∙year−1 to this wetland community.