The reduction of root colonization by mycorrhizal fungi by mycophagous amoebae

Abstract

Two mycophagous amoebae, Saccamoeba sp. and Gephyramoeba sp., reduced the colonization of pine roots in soil by the ectomycorrhizal fungus, Rhizopogon luteolus, when added at the same time as the fungus or 2 weeks later. Another mycophagous amoeba, an unidentified leptomyxid, was unable to do so. When seedlings were grown in sterilized soil amended with different population levels of Saccamoeba, 42 and 85 amoebae g soil−1 had no effect but large reductions in root colonization by R. luteolus occurred when 430 and 860 amoebae g soil−1 were added. After 4 weeks, however, the protozoa population increased to a similarly high level in all treatments irrespective of the numbers added initially. Our results indicate that protozoa can have a large effect on the establishment of inoculated symbiotic fungi and could markedly affect the microbial composition of the rhizosphere.