Effect of rhizobial inoculations on nitrogen metabolism of Albizia lebbek seedlings

Abstract

Rhizobia were isolated from Albizia lebbek (L) Benth. seedlings collected from six different places, tested against the nodulation test and inoculated into 45 day old Albizia lebbek seedlings in sterile soil mixture under glass house conditions. After a period of two and three months, the plant samples were taken to study the influence of inoculation treatments on nitrogen fixation, assimilation, biomass production and nitrogen content in different plant parts. The seedlings inoculated with isolates III(1) and III(2) of Lalpani had the maximum nodular biomass, specific (13.73 and 13.59 μ mole C2H2 reduced h−1, respectively) and total nitrogenase (11.80 and 11.16 μ mole C2H2 reduced h−1, respectively) activities in their nodules statistically at par with each other. These also exhibited high nitrate reductase activity in different plant parts. The seedlings inoculated with slow growing isolates viz. I(2) and IV(1) and the control were amongst poor performers for biomass production, nitrogenase activity and nitrate reductase activity in different plant parts. The minimum nitrogenase (specific and total) activities and low nitrogen content (%) in leaves, stems and roots were estimated in seedlings inoculated with isolate II(4) of Barkot. Nodular biomass was recorded as an indicator of nitrogen fixation activity rather than the number of nodules per plant. The isolates III(1) and III(2) can be utilized to enhance productivity in afforestation and reforestation programmes.