Water repellency, mat formation, and leaf-stimulated growth of some ectomycorrhizal fungi

Summary

Ectomycorrhizal short roots, mycelia, rhizomorphs and mats from conifer soil were examined in relation to their hydrophobic properties. In some cases connected fruit bodies were included in the study. Mycorrhizal soils gathered from the forest and/or colonized in a laboratory rhizoscope were studied, as were mycelia in pure culture. Most forest-derived species were hydrophobic. The drought-resistant Cenococcum geophilum and the more ruderal and moisture-dependent Thelephora terrestris were both strongly hydrophilic. The hydrophobic mycelium seemed solely responsible for the water repellence properties, and adjacent soil and plant debris remained unaffected and hydrophilic. In hydrophobic fungi, mat formation was induced in the rhizoscope by hyphal contact with alder litter leaves. This stimulating effect was not found when the leaves were covered by water or when fresh, green alder leaves were used. Thelephora terrestris did not form such mats in vitro and spread sparsely in air pockets as well as in the adjacent water film. The possibility is discussed that many mycorrhizal fungi in the forest may partly control their soil environment via aeration created by their hydrophobia.