Nitrogen fixation associated with grasses and cere

Authors: Robert M Boddey Johanna Dobereiner

Publish Date: 1995

Volume: , Issue: , Pages: 241-250

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Abstract

Over the last 20 years many new species of N2fixing bacteria have been discovered in association with grasses cereals and other nonnodulating crops Virtually all of these bacteria are microaerophylic fixing N2 only in the presence of low partial pressures of oxygen Until a few years ago much attention was focussed on members the genus Azospirillum and it was assumed that N2 fixation was restricted to the rhizosphere or rhizoplane of the host plants Through the use of N balance and 15N techniques it has been shown that in the case of lowland rice several tropical pasture grasses and especially sugar cane the contributions of biological N2 fixation BNF are of agronomic significanceMore detailed study of the N2fixing bacteria associated with sugar cane Acetobacter diazotrophicus and Herbaspirillum spp has shown that they occur in high numbers not only in roots of this crop but also in the stems leaves and trash but are rarely found in the soil Some of these endophytic diazotrophs have now also been found in forage grasses cereals sweet potato and cassava although evidence of significant BNF contributions is still lackingThe identification of these endophytic diazotrophs as the organisms probably responsible for the high contributions of N2 fixation observed in sugar cane suggests that it may be possible to attain significant BNF contributions in some other gramineae and perhaps root crops

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