Influence of leaves on sporophore production by fungi forming sheathing mycorrhizas with Betula spp.

Abstract

MOST of the intimate and often beneficial associations formed between plant roots and some soil fungi can be classified as either endomycorrhizas of various types or sheathing (ecto-) mycorrhizas^1,2. The latter, in which colonised roots are shorter and thicker than their uncolonised counterparts, are mainly attributed to basidiomycetous fungi that produce sporophores (toadstools) typical of the Agaricales. Sometimes fungi forming sheathing mycorrhizas produce large numbers of sporophores. P. Larsen, quoted by Romell³, estimated sporophore production by the mycorrhizal Suillus bovinus (Fries) O. Kuntze to be about 180 kg (dry weight) per hectare per yr. Although their evidence is questionable, experiments done by Romell⁴ and Laiho⁵ suggest that the mycorrhizal Boletus subtomentosus Fries and Paxillus involutus (Batsch ex Fr.) Fr. usually form sporophores only if they are organically linked to living trees. Hacskaylo⁶ found that shading foliage of Pinus virginiana Mill decreased sporophore formation by Thelephora terrestris Fr. The results reported here extend the understanding of this relation by showing that sporophore production by some mycorrhizal associates of birch (Betula spp.) is strongly dependent, in the field, on the presence of green foliage.