DISTRIBUTION OF HETEROTROPHIC AEROBIC MICROFLORA AND SPECIALLY DENITRIFYING AND FREE-LIVING NITROGEN-FIXING BACTERIA IN THE RHIZOSPHERE OF RICE

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  • 1 January 1980
    • journal article
    • research article
    • Vol. A131  (2) , 197-207
Abstract
The distribution of heterotrophic aerobic bacteria, actinomycetes and fungi was estimated in 3 samples (rhizospherical soil (SR), rhizoplane (R) and endorhizosphere (ER)) obtained from 1 rice seedling which had grown in a pot during 4 mo. in a Casamance grey soil. The number of microbial populations were about the same from 1 sample to another: 1.1-2 .times. 108 bacteria, 3.3-8.6 .times. 106 actinomycetes and 0.2-8.9 .times. 104 fungi/g of dry soil (SR) or dry roots (R and ER). The denitrifying and free-living N2-fixing bacteria were numerous (107 bacteria/g) but lower for ER where the number of actinomycetes remained high. Thirty-six bacterial strains were isolated from every sample with the use of a grid for isolation. Gram-negative bacteria were dominant in SR and R where they represented 70 and 94%, respectively, of the total count. The major groups were nonsporulated gram-variable rods (SR) and Alcaligenes-like bacteria (ER). The pseudomonads represented 15% of total count in the 3 samples. The frequency of endospore-forming gram-positive bacteria was high only in R where the Bacillus group was estimated to 45% of total count. Only 5 free-living N2-fixing bacterial strains showed denitrifying ability.