THE RHIZOSPHERE EFFECT OF MYCORRHIZAL AND NON-MYCORRHIZAL ROOTS OF YELLOW BIRCH SEEDLINGS

A study of the surface microflora of mycorrhizal and non-mycorrhizal roots of yellow birch seedlings has revealed distinct quantitative and qualitative differences. Higher bacterial counts and distinctly greater numbers of actinomycetes and of methylene-blue-reducing, sugar-fermenting, ammonifying, and fluorescent-pigment-producing bacteria were found on the former. The percentage incidence of bacteria growing optimally in a simple mineral–glucose medium was greater on normal roots whereas bacteria requiring complex nutritional factors appeared to be relatively more numerous on the mycorrhizal surface. Species of Pythium, Fusarium, and Cylindrocarpon predominated on, and Mycelium radicis (?) was absent from, normal roots, whereas, on mycorrhizal roots, Penicillium and other rapidly growing fungi as well as Mycelium radicis (?) were numerous and Pythium and Fusarium species absent. These results are discussed in relation to the nutrition of mycorrhizal and non-mycorrhizal roots.