Growth performance and nodulation response of Acacia mangium co-inoculated with Bradyrhizobium sp. and Pisolithus tinctorius

Abstract

A study was conducted to find out if co-inoculation with N 2-fixing Bradyrhizobium sp. and P-solubilizing ectomycorrhizal Pisolithus tinctorius can provide the synergistic effects for the growth of Acacia mangium under both N and P deficient conditions. Total dry matter production, and N and P contents were significantly higher in seedlings that received dual inoculation in the absence of both mineral N and soluble P than in uninoculated control seedlings that received similar nutrient supply. Individual inoculation of Bradyrhizobium or P. tinctorius failed to enhance seedling growth under both N and P deficiency. Seedlings that received dual inoculation also performed better than uninoculated control seedlings that received both nutrients in the available form and seedlings that received Bradyrhizobium and soluble P. However, presence of P. tinctorius did not have a stimulatory effect on nodule formation and functioning. Percentage dry matter allocated to nodules, specific nodule number (number of nodules formed g -1 of total dry matter produced) and specific nitrogenase activity (mmoles ethylene produced h-1g-1 of nodule dry weight) were significantly lower in seedlings that received dual inoculation when compared to seedlings that received Bradyrhizobium and soluble P. Relatively poor formation of nodules in seedlings that received dual inoculation could be due to competition for carbon between the plant and microbial symbionts in this tripartite symbiotic association. Future studies should focus on carbon partitioning between these two microbial symbionts during their association with the host plant. Also, studies are required to identify the fungal compounds that may be involved in restriction or regulation of nodule growth during ectomycorrhiza formation. ©2005 Balaban.