1. Disturbance is assumed to be a major driver of plant community composition, but whether similar
processes operate on associated soil microbial communities is less known. Based on the assumed
trade-off between disturbance tolerance and competiveness, we hypothesize that a severe disturbance
applied within a semi-natural grassland would shift the arbuscular mycorrhizal (AM) fungal
community towards disturbance-tolerant fungi that are rare in undisturbed soils.
2. We used 454-sequencing of the large subunit rDNAregion to characterizeAMfungal communities
in Plantago lanceolata roots grown in the field for 4 months and exposed either to no disturbance
or to severe disturbance where fungi from undisturbed soil were either permitted or
prevented from re-colonizing the disturbed area. This allowed for a distinction between AM fungi
that survived the disturbance and those that quickly re-colonized after a disturbance. To identify
AMfungi that could potentially colonize the experimental plants, we also analysed roots from adjacent,
undisturbed vegetation.
3. We found 32 fungal operational taxonomic units (OTUs) distributed across five knownAMfungal
families. Contrary to our expectations, disturbance did not significantly alter the community
composition and OTU richness. Instead, OTU abundances were positively correlated across treatments;
i.e., common OTUs in undisturbed soil were also common after the severe disturbance.
However, the distribution of OTUs within and between plots was largely unpredictable, with
approximately 40%of all sequences within a sample belonging to a single OTU of varying identity.
The distribution of two plant species that are often poorly colonized by AMfungi (Dianthus deltoides
and Carex arenaria) correlated significantly with the OTU composition, which may indicate
that host quality could be an additional driver of fungal communities.
4. Synthesis. Our results suggest that factors other than disturbance drive the relative abundance of
OTUs in this grassland and question the long-held assumption that communities shift in a predictable
manner after a disturbance event. The reassembly of this fungal community indicates a high
community resilience, but substantial local stochasticity and dominance by single OTUs, which
could be due to priority effects among abundantAMfungi possessing a similar – and high – degree
of disturbance tolerance.