Associative rhizosphere nitrogen fixation (acetylene reduction) among plants from Ohio peatlands

The macrophytes of wetlands are known, and in some cases, the nitrogenase activity (NA) of these plants has been examined as well. This activity, however, has been only partially studied in peatlands, particularly in northeastern Ohio where numerous peat-forming bogs and fens are located. We tested 18 flowering plants and 1 Bryophyte inhabiting peatlands in this region of the United States for potential rhizosphere nitrogen fixation using the acetylene reduction technique. The roots and adherent soil of selected plants from 3 bogs (Fern Lake, Kent, and Triangle Lake) and 1 fen (J. Arthur Herrick) were tested for ethylene evolution following incubation under an acetylene atmosphere. NA was observed at each peatland, and 89% of the plants tested were NA positive. The signature plants of the bogs, Chamaedaphne calyculata, and the fen, Potentilla fruticosa, were NA positive, whereas Sphagnum spp. was negative at 2 of the 4 peatlands. The highest rates of NA were associated with Typha spp. where the mean rates for ethylene evolved by Typha angustifolia rhizosphere were 233.2 nmoles g Dry Mass^-1 24 h^-1 and 407.2 × 10² nmoles m^-2 24 h^-1. Rhizosphere NA of 3 previously unstudied plants (Acorus americanus, Decodon verticillatus and Symplocarpus foetidus) are given. Diazotroph relationships directly and indirectly enrich the associated plants and soil with nitrogen such that the success of newly constructed or reclaimed wetlands may be fostered by inclusion of plant species known to harbor associative diazotrophs. The widespread occurrence and frequency of nitrogen fixation in these habitats argues for inclusion of this activity during investigative and management studies of wetlands.