Changes in Microfungal Communities in Roots of Quercus robur Stumps and their Possible Effect on Colonization by Armillaria

Sixteen fungal communities were sampled by isolating from 0.5–1 cm diameter roots of living trees and stumps of common oak (Quercus robur). The density of fungi was 1.5–2 times greater in roots from stumps than from living trees. The diversity of fungi was similar in living tree roots and stumps. Some of the fungal species with increased densities in stump roots (e.g. Aspergillus kanagawaensis, Chrysosporium pannorum, Cylindrocarpon destructans, C. didymum, Hormiactis candida, Monodictys lepraria, Mycelium radicis atrovirens, Penicillium daleae, P. janczewskii, and Trichocladium opacum) usually stimulated the growth of rhizomorphs of either Armillaria ostoyae or A. gallica in oak‐wood segments in vitro. Eight of 27 isolates that were studied stimulated the rhizomorph growth in both Armillaria spp. It is presumed that the increase in density of `stimulants' may predispose oak stumps to infection by A. ostoyae and A. gallica.