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

Estimated rates of N fixation for plants growing in submerged soils kg ha^_1yr^-1 are Typha latifolia, 0.91; Carex stricta, 0.47; Calamagrostis canadensis 0.24; and Lemna minor, 1.90. Significantly higher fixation rates were found with plants growing in submerged areas than with those on the well-drained shore, 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 the N fixation may be an important source of N in developing seeds. Overall, N fixation was estimated to supply 11 kg N ha^-1yr^-1 to this wetland community. -from Authors