Nitrogen-Fixing (Acetylene Redution) Activity and Population of Aerobic Heterotrophic Nitrogen-Fixing Bacteria Associated with Wetland Rice

Abstract

Nitrogen-fixing activity associated with different wetland rice varieties was measured at various growth stages by an in situ acetylene reduction method after the activities of blue-green algae (cyanobacteria) in the flood water and on the lower portion of the rice stem were eliminated. Nitrogen-fixing activities associated with rice varieties differed with plant growth stages. The activities increased with plant age, and the maximum was about at heading stage. The nitrogen fixed during the whole cropping period was estimated at 5.9 kg of N per ha for variety IR26 (7 days) and 4.8 kg of N per ha for variety IR36 (95 days). The population of aerobic heterotrophic N2-fixing bacteria associated with rice roots and stems was determined by the most-probable-number method, using semisolid glucoseyeast extract and semisolid malate-yeast extract media. The addition of yeast extract to the glucose medium increased the number and activity of aerobic heterotrophic N2-fixing bacteria. The glucose-yeast extract medium gave higher counts of aerobic N2-fixing bacteria associated with rice roots than did the malateyeast extract medium, on which Spirillum-like bacteria were usually observed. The lower portion of the rice stem was also inhabited by N2-fixing bacteria and was an active site of N2 fixation. on July 7, 2020 by guest http://aem.asm.org/ Downloaded from

Enumeration and Identification of Nitrogen-Fixing Bacteria from Forage Grass Roots

“…A comparison of counts obtained in this study with those obtained by other investigations is not fully acceptable because different techniques were utilized. However, the counts are within the range reported by others (2,11,17).…”

“…Published information on this topic is very limited. Correlations between AR activity and numbers of diazotrophic bacteria in soil (9) and on rice root segments (17) are poor. Close correlation between population size and N2 fixation is sporadic in occurrence because N2 fixation is growth linked and dependent upon cell proliferation (4).…”

Limitation of N2 fixation in coastal marine waters: Relative importance of molybdenum, iron, phosphorus, and organic matter availability1

“…matter-enriched microzones are certainly not confined to marine habitats. Such requirements reflect conditions known to favor the development and proliferation of free-living, N,-fixing soil microorganisms (Brouzes et al 197 1;Okafor and MacRae 1973;Rajaramamohan-Rao 1976), legume (root nodule) -associated symbiotic N2 fixers (Hardy et al 1976), and rhizosphere (non-nodulated) -associated N2 fixers among various terrestrial and aquatic plants (Dommergues et al 1973;Tjepkema and van Berkum 1977;Watanabe et al 1979), including Spartina (Patriquin 1978;McClung et al 1983) and Juncus (Tjepkema and Evans 1976). We accordingly conclude that limitations on the distributions and magnitudes of marine N2 fixation are in part the result of the evolution of an oxygen-rich biosphere that has placed severe constraints on suitable habitats.…”

Enumeration and Localization of N 2 -Fixing Bacteria Associated with Roots of Spartina alterniflora Loisel

“…Bacteria were recovered from root surfaces by shaking 2.0-g (fresh weight) subsamples with 3.0 g of glass beads (equal weights of beads 3 and 5 mm in diameter) in 20 ml of sterile SPB in 125-ml Ehrlenmeyer flasks at 400 rpm for 15 min on a New Brunswick Gyrotory shaker. The bacteria recovered in the SPB from the roots shaken with glass beads were defined, according to Watanabe et al (24), as the rhizoplane population. In one experiment, subsamples of this rhizoplane population in SPB were homogenized to determine whether this treatment affected the recovery of bacteria.…”