Publication Date

1993

Description

Isotopic 15N fractionation during N2 fixation by Centrosema acutifolium, C. brasilianum and C. macrocarpum grown in N·free sand-nutrient solution was investigated as a prerequisite for the use 9f the natural 15N abundance method to estimate N2 fixation. The natural abundance of 15N was always lower in shoots than in roots and nodules, and there was little difference between species. In contrast, inoculation strongly influenced isotopic fractionation, leading to average o15N shoot values of -0.64 and -1.37 for Bradyrhizobiumstrains CIAT3101 and 1670 respectively, given adequate phosphorus. P deficiency led to a small legume x P interaction but only with strain 3101. Field measurements of N2 fixation by the tsN natural abundance method and 15N isotope dilution technique showed similar increases in N2 fixation after alleviating P deficiency. However, estimates of N2 fixation were higher using the natural 15N abundance method, possibly due to the effect of mixed infection by competitive native strains of Bradyrhizobium.

Share

COinS
 

Use of Natural 15N Abundance in Estimating Nitrogen Fixation by Centrosema spp: Influence of Phosphorus and Strain of Bradyrhizobium

Isotopic 15N fractionation during N2 fixation by Centrosema acutifolium, C. brasilianum and C. macrocarpum grown in N·free sand-nutrient solution was investigated as a prerequisite for the use 9f the natural 15N abundance method to estimate N2 fixation. The natural abundance of 15N was always lower in shoots than in roots and nodules, and there was little difference between species. In contrast, inoculation strongly influenced isotopic fractionation, leading to average o15N shoot values of -0.64 and -1.37 for Bradyrhizobiumstrains CIAT3101 and 1670 respectively, given adequate phosphorus. P deficiency led to a small legume x P interaction but only with strain 3101. Field measurements of N2 fixation by the tsN natural abundance method and 15N isotope dilution technique showed similar increases in N2 fixation after alleviating P deficiency. However, estimates of N2 fixation were higher using the natural 15N abundance method, possibly due to the effect of mixed infection by competitive native strains of Bradyrhizobium.