Evaluation for dinitrogen fixation of induced wheat nodules by 15N isotope dilution method

The results in pot experiments showed that the treating of 2,4-D and Azorhizobium caulinodans (2,4-D+A) could induce para-nodule formation on wheat roots. Plants treated grew normally. The plant height and dry weight are significantly higher than reference plants which are treated with 2,4-D+azorhizobium sterilized (2,4-D+AS). The nitrogenase activity is detected by ARA method. The N yield of most treated plants, especially in root systems, is higher than reference group that is measured by Kjeldahl method. The atom % 15N excess in leaf and stem of treated plants measured by 15N isotope dilution method is lower than that of reference group. Through four years experiments, it shows that para-nodules of wheat treated with 2,4-D+A could fix N2 from air, but the ability of nitrogen fixation is lower and unstable. Although the nodulation efficiency could reach 100%, not each para-nodule induced can present activity of dinitrogen fixation. The amount of N fixed is 0.05∼18.1 mg/pot (0.01∼3.87 mg/plant). The net %Ndfa is 2.32%∼18.07%. The free-living N2 fixing activity of azorhizobium is detected by 15N isotope dilution method. The calculation of %Ndfa of nodulated wheat accurately is also discussed