Studies of pathogenic and antagonistic microfungal populations and their potential interactions in the mycorrhizoplane of Norway spruce (Picea abies (L.) Karst.) and beech (Fagus sylvatica L.) on acidified and limed plots

Recent tree decline was hypothesized to be connected to root damage caused by soil acidification and increased frequency of pathogenic root colonizing fungi. The rhizoplane is constituted by the mycorrhizal sheath and a high diversity of microfungi, some of which are known to behave antagonistically against pathogens. Disturbance of the balance between pathogens and antagonists by soil acidification may endanger the health of tree roots. Liming may stabilize the interactions. The microfungal populations connected to the mycorrhizoplane of Norway spruce (Picea abies) and beech (Fagus sylvatica) were, therefore, investigated on experimental Norway spruce plots that had been treated with acidified water or were limed. Beech presented the original forest and was left untreated. Eight microfungal species known as either pathogenic or antagonistic, Trichoderma viride, T. hamatum, T. polysporum, Cylindrocarpon destructans, Sesquicillium candelabrum, Mycelium radicis atrovirens, Tolyplocladium geodes and Oidiodendron maius, were isolated from the mycorrhizoplanes and their abundance in the five different plots compared. Acidification enhanced the frequency of Mycelium radicis atrovirens and Oidiodendron maius but reduced Trichoderma viride. Liming promoted Sesquicillium candelabrum and Cylindrocarpon destructans. Detailed analysis of the population patterns indicated that changes in the frequency of a particular fungal species may not only be caused by shift of chemical soil factors but also by antagonistic interactions between the microfungi, thus reducing pathogenic attacks on rootlets.