Use of 15N Isotope Dilution Technique for Quantification of Associative BNF in Kallar Grass

Abstract

Biological nitrogen fixation associated with the roots of Kallar grass (Leptochloa fusca), a salt tolerant grass, has been earlier demonstrated by us using acetylene reduction technique with excised roots. Presently we report here results of quantitative estimation of BNF in Kallar grass when grown under controlled conditions in nutrient solution and inoculated with N2 fixing bacteria, using 15N isotope dilution technique. Three bacteria namely Klebsiella pneumonae (strain NIAB-1) Biejrinckia gumosa (Strain ISO-2) and Azospirillum brasiliense were used. First two strains have been isolated from Kallar grass roots. All the treatments received (15NH4)2SO4 50% a.e. at the rate of 0.5 mg/50 ml nut.solu. The plants were grown in a growth room for 4 weeks with adequate facilities of light and temperature of 28±2°C. After harvest acetylene reduction of roots, total yield, total N and 15N analyses were made. In case of control (uninoculated) no acetylene reduction was observed whereas all other inoculated treatments were able to reduce acetylene which confirmed the presence of microorganisms. Total N in inoculated treatments was 2–3 times higher than in control and so were the fresh and dry weight yields.