Helevecio De-PolliElichi MatsuiJohanna DobereinerEneas Salati2014-05-242014-05-241977Sol. Biol. Biochem., Vol 9, pp. 119-123http://hdl.handle.net/123456789/1753Intact soil cores containing plants of Paspalum notation or Digitaria decumbens were selected with the acetylene reduction method, and then exposed to 15N2 to confirm nitrogen fixation in tropical grass-bacteria associations. In a preliminary experiment with P. notatum 15N2 incorporation was slow but progressive during 24 h in roots but translocation to rhizomes and leaves ceased after 17 h. With improved assay chambers, enrichments of 0.151 and 0.563 15N atom % excess were obtained in roots of D. decumbens cv transvala and P. notatum systems respectively, after 3 days. Enrichments in rhizomes were similar to those of roots; however in the leaves only 8% of root enrichment was observed. The addition of sucrose to the soil doubled N2-fixation in roots in both grass species studied, but did not result in increased incorporation into the leaves of P. notatum.enArticle