Nitrogen fixation associated with Scirpus atrovirens and other nonnodulated plants in Massachusetts

K,ZNA, T. M., and J . D. TJEPKEMA. 1978. Nitrogen fixation associated withScirprrs trtral.i~.etl.s and other nonnodulated plants in Massachusetts. Can. J . Bot. 56: 26362640. Nitrogen fixation was measured using the acetylene reduction technique in soil cores of 13 nonnodulated. herbaceous plant species growing in mesic and wetland habitats. Six species that grew in a well-drained portion of an old field exhibited low rates of N2 fixation (7 g N. ha-I. dayI ) . A bulrush. Scirprts rrtro\,it.o~s, which grew in an area of compacted soil in the old field, showed nmoder;~te rate of N2 fixation (30l o g N . ha-' . d a y 1 ) . These old field species exhibited lag of only a few hours before a constant late of acetylene reduction occurred. The estimated rates for the six wetland species were generally higher, and there was a lag such that the activity was still increasing after 20 h of incubation. NZ fixation in cores of S . (rtwviretrs was primarily associated with the roots and adhering soil. Incubation ofthe cores in N1 for24 h caused a fourfold increase in the acetylene reduction late over that in air. although the rates during the first 4 h were sirnil:~r.