Nitrogen Fixation (Acetylene Reduction) by Forest Legumes: Sensitivity to Pre‐harvest and Assay Conditions

Abstract

SUMMARYThe effects of enwronmental and methodological factors on acetylene reduction by nodules of Acacia pulchella R.Br., Kennedia coccinea Vent, and K. prostrata R.Br. grown in pots were studied.The time course of acetylene reduction, measured for each species during assays lasting up to 3 h, showed that there was an initial lag phase before maximum rates were reached and that rates then declined rapidly. This decline in activity was less marked for K. prostrata than for the other two species. Rates of acetylene reduction did not differ significantly between detached nodules, roots with attached nodules and whole plants.Delaying the introduction of acetylene into assay vessels indicated that the decline in nitrogenase activity during assays at higher temperatures was only partly caused by the acetylene substrate. As weights of nodules were small in relation to the volume of assay vessels, the decline in activity is unlikely to result from changes in pOj. The initial lag phase was shorter and the decline in activity with time more marked with increasing temperature. This finding has important implications for conducting and interpreting field assays, and in determining optimum temperatures for nitrogenase activity.Calibration factors relating acetylene reduction to nitrogen fixation were estimated from measurements of nitrogen accumulation and acetylene reduction during grow th of young plants in a nitrogen-free sand. Ratios for A. pulchella (2-5:1) and K. coccinea (2-4:1) were lower than theoretical ratios (3 to 4:1), probably because of the decline in rates of acetylene reduction during assays. Lowering of irradiance to about 4°o of full sunlight over 2d depressed acetylene reduction rates by 58% for A. pulchella and by 36 °o for K. coccinea.

Actinobacteria as Plant Growth-Promoting Rhizobacteria

“…These vesicles are in charge of protecting the nitrogenase complex. These actinobacteria have been extensively reported by several authors [59][60][61], due to its fixation characteristics that have been confirmed by acetylene reduction method [62][63][64]. The morphology of the bacteria cultured in our laboratory facilities using Nfb media did not display any similarity with Frankia sp, since different microscopic descriptions such as long and short filaments, tortuous or spiral-shaped filaments were found.…”

Caractéristiques symbiotiques et génotypiques des Rhizobia associés àAcacia saligna(Labili.) Wendl. dans quelques pépinières en Algérie

“…Douze semaines après inoculation, les plantules sont déterrées et leur système racinaire est lavé à l'eau du robinet et rincé avec de l'eau distillée stérile. Les nodules des plants d'un même pot sont excisés et leur pouvoir fixateur d'azote est déterminé par la mesure de leur ARA (activité réductrice de l'acétylène (C 2 H 2 ) en éthylène (C 2 H 4 )) selon la méthode préconisée par Grove et Malajczuk (1987). Les nodules sont alors mis à sécher à 65 °C pendant 96 heures et leur poids sec est déterminé.…”