GRASS RHIZOSHEATHS: ASSOCIATED BACTERIAL COMMUNITIES AND POTENTIAL FOR NITROGEN FIXATION

Rhizosheaths are structures composed of mucilage secreted from plants and adherent soil particles that form it cylinder around the root. Using scanning electron microscopy (SEM), we observed bacteria associated with rhizosheaths of the grasses Achnatherum hymenoides, Calamovilfa longifolia, Hesperostipa comata, and Pascopyrum smithii from a sand little area in Harding County in northwestern Smith Dakota. The greatest numbers of bacteria, observed with SEA (529 mm(-2)), and the greatest number of culturable bacteria (9.9 X 10(7) CFU . g(-1) or 5178 CFU . mm(-2)) were oil rhizosheaths of C. longifolia. Rhizosheaths of all the grasses examined contained a higher density of bacteria than the surrounding soil. Nitrogen fixation, as assayed by reduction of acetylene to ethylene, was present in sonic rhizosheaths. Bacterial nifH gene sequences amplified front bacteria associated with rhizosheaths were most similar to those from Alcaligenes latus and Mesorhizobium loti.