Interaction among N-fixing bacteria and AM fungi in Amazonian legume tree (Schizolobium amazonicum) in field conditions

The Amazon forest has suffered an accelerated degradation process due to cutting to implant agricultural systems, pasture and electricity generation projects and disorganized mining and wood exploitations. The challenge is to develop new technologies for wood production in agroforestry systems. Schizolobium amazonicum is a legume tree, with fast growth and its wood is employed to make furniture. More and more areas have been sowed with S. amazonicum, but this production system is very poor technologically. In the present paper we proposed to evaluate the effect on the plant growth and plant survival of three arbuscular mycorrhizal fungi (Glomus clarum, Glomus intraradices and Glomus etunicatum) associated with three N-fixing bacteria strains (two Rhizobium sp. and one Burkholderia sp.). Two methods of planting were used: direct sowing or transplantation of seedlings after initial growth in nursery. G. intrarradices was more effective in plant growth when inoculated in seed, and the bacteria strains had no effect when inoculated alone or with AM fungi. However, in seedlings the dual inoculation was more effective. At 210 days Rhi1 and Rhi2 associated with G. clarum or G. etunicatum increase plant growth. At 390 days G. clarum associated with LEM6 or Rhi1 increased most of the parameters evaluated, including biomass and wood production. Direct sowing is the traditional method largely used in the non-tillage areas and was more ineffective. The presence of microorganisms showed significant differences when compared with non-inoculated plant. The results suggested that some microbial combinations were effective in stimulating plant growth, but further experiments need to be carried out to evaluate which N-fixing bacteria and AM fungi is more effective for each planting systems for S. amazonicum.