SOIL PROTOZOA AND FOREST TREE GROWTH - NON-NUTRITIONAL EFFECTS AND INTERACTION WITH MYCORRHIZAE

Mycorrhizal (Lactarius rufus Fr.) and non-mycorrhizal Norway spruce se edlings (Picea abies Karst.) were grown in a sand culture and inoculat ed with protozoa (naked amoebae and flagellates) extracted from native forest soil or with protozoa grown on agar cultures. A soil suspensio n from which the protozoa were eliminated by filtration or chloroform fumigation was used as a control. After 19 weeks of growth in a climat e chamber at 20-22 degrees C, the seedlings were harvested. Protozoa r educed the number of bacterial colony-forming units extracted from the rhizoplane of both non-mycorrhizal and mycorrhizal seedlings and sign ificantly increased seedling growth. However, concentrations of minera l nutrients in needles were not increased in seedlings with protozoan treatment. It is concluded that the increased growth of seedlings was not caused by nutrients released during amoebal grazing on rhizosphere micro-organisms. The protozoa presumably affected plant physiological processes, either directly, via production of phytohormones, or indir ectly, via modification of the structure and performance of the rhizos phere microflora and their impact on plant growth. Mycorrhizal coloniz ation significantly increased the abundance of naked amoebae at the rh izoplane. Our observations indicate that protozoa in the rhizosphere i nteract significantly with mycorrhizae.