CARBON METABOLISM OF SPARTINA ALTERNIFLORA LOISEL IN RELATION TO THAT OF ASSOCIATED NITROGEN‐FIXING BACTERIA

Abstract

Relationships between the carbon metabolism of the C4 salt‐marsh grass, Spartina alterniflora Loisel, and that of root and rhizosphere soil diazotrophs were investigated. Experiments involving addition of carbon compounds demonstrated that acetylene reducing activity (ARA) of both populations was dependent upon compounds from roots soluble in 80% ethanol. Of these, sugars (glucose, fructose and sucrose) were most effective in increasing ARA of the soil diazotrophs, while organic acids (malate) increased ARA of root diazotrophs. ARA of both populations was dependent upon carbon sources from large carbon pools. 14CO2 labelling of plants demonstrated that sugars were the only quantitatively significant photosynthates translocated to the roots and that these entered large carbon pools. After longer periods, labelled sugars were detected in rhizosphere soils where they were metabolized (possibly by diazotrophs) to form acidic and basic compounds. The possibility that dark CO2 fixation by roots or bacteria provided malate for the root diazotrophs was investigated. Copyright © 1981, Wiley Blackwell. All rights reserved