Effectiveness of Arbuscular Mycorrhizal Fungus (Glomus aggregatum) in Increasing Acacia Koa Tolerance to Al and Mn Toxicities in Acid Soils.

High concentrations of aluminum (Al) and/or manganese (Mn) constrain plant productivity in many acid soils.  A greenhouse experiment was conducted in order to determine the extent to which an arbuscular mycorrhizal (AM) fungus (Glomus aggregatum) could enhance the establishment and growth of Acacia koa in acid soils containing toxic levels of Al and Mn.  In the acid soil containing toxic level of Al, roots of plants started with seedlings pre-colonized by G. aggregatum had higher levels AM fungal colonization than roots of plants not initially colonized by the fungus.  Pre-colonization with G. aggregatum led to significant increase in root and shoot dry matter yield in the presence of toxic levels of Al.  However, root and shoot dry matter yield and shoot dry matter yield were further increased if the concentration of Al in the soil solution was decreased by liming. In the Mn-toxic soil, inoculation with AMF had increased AMF colonization of roots but not roots or shoot dry matter yield if the soil was not limed.