Ectomycorrhizal mycelia reduce bacterial activity in a sandy soil

Abstract

Bacterial activity was studied in a growth system containing Pinus c~ntorfa seedlings inoculated with different mycorrhizal fungi. Nylon nets enabled separation of soil compartments with extramatrical mycorrhizal hyphae from soil compartments with roots and mycelium. In three separate experiments bacterial activity, estimated as thymidine incorporation , was reduced in soils with Puxillus involutus hyphae compared to controls without mycorrhizal hyphae. This effect was found irrespective of compartments with and without roots were compared. Luccaria bicolor only reduced the activity in one of these three experiments. Thelephora terrestris (tested in two experiments), Lmcariu proxima, Suillus variegatus and Hebelom crustulinifome (one experiment), also reduced the thymidine and leucine incorporation rates of bacteria. The reduction for these fungi varied between 20% and 50% in all experiments. Numbers of viable bacteria appeared to be reduced by T. terrestris, L. proxima, S. variegatus and H. crustulinifome in one experiment, while no effect was seen in the other experiments.