Soil disturbance influences ectomycorrhizal fungal communities: an in-situ experiment under Mediterranean holm oak (Quercus ilex L.).

The functioning of temperate forests is based on a symbiosis linking trees to a vast diversity of ectomycorrhizal (EM) fungi. Although disturbance is a major driver of biodiversity patterns in these ecosystems, its effects on the fine-scale distribution and the short-term dynamics of EM fungal communities are still largely unknown. We used an in situ experiment combined with the analysis of the ITS rDNA region of EM root tips to compare the composition of fungal communities before and one year after small-scale soil disturbance simulating animal bioturbation. Disturbance induced a transient increase in EM root tip abundance, a 56.3% decrease in species richness and a marked composition turnover. One year after disturbance, the proportion of Ascomycota had increased by 38.5% to represent 49.3% of the total number of mycorrhizae. This shift was associated with an increase in Pezizales (Tuberaceae, Helvellaceae, Pezizaceae and Pyronemataceae) and a decrease in Russulaceae, Cortinariaceae and Hydnaceae. The results show that small-scale soil disturbances promote highly localized fungal successions, from late-colonizing Basidiomycota lineages to early-colonizing Ascomycota. In temperate ecosystems, asynchronous small-scale disturbances may contribute to ectomycorrhizal community richness (α-diversity) and spatial turnover (β-diversity) by generating fine-scale spatial heterogeneity within forests.