Nitrogen fixation associated with natural and cultivated stands of Typha latifolia L. ( Typhaceae).

The rate of acetylene reduction in a natural cattail population was c4-fold higher than in a cultivated cattail stand. Nitrogenase activity principally occurs in the rhizosphere of roots and rhizomes, with greatest activity occurring in association with mature roots. Bacterial associations were limited to the rhizoplane of this angiosperm. One diazotrophic bacterial genus was associated with roots and rhizomes and was identified as the facultative anaerobe Bacillus. Contribution of free-living cyanobacteria to total N-fixation in the natural stand was negligible. A natural stand of cattails may fix 18 kg N ha^-1 yr^-1 or c8.2% of the total N present in the standing crop. -from Author