Summary 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 rDNA region to characterize AM fungal 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 AM fungi 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 known AM fungal 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 AM fungi (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 abundant AM fungi possessing a similar -and high -degree of disturbance tolerance.

While the effect of disturbance on overall abundance and community composition of arbuscular mycorrhizal (AM) fungi has been researched in agricultural fields, less is known about the impact in semi-natural grasslands. We sampled two AM plant species, Festuca brevipila and Plantago lanceolata, from an ongoing grassland restoration experiment that contained replicated plowed and control plots. The AM fungal community in roots was determined using nested PCR and LSU rDNA primers. We identified 38 phylotypes within the Glomeromycota, of which 29 belonged to Glomus A, six to Glomus B, and three to Diversisporaceae. Only three phylotypes were closely related to known morphospecies. Soil disturbance significantly reduced phylotype richness and changed the AM fungal community composition. Most phylotypes, even closely related ones, showed little or no overlap in their distribution and occurred in either the control or disturbed plots. We found no evidence of host preference in this system, except for one phylotype that preferentially seemed to colonize Festuca. Our results show that disturbance imposed a stronger structuring force for AM fungal communities than did host plants in this semi-natural grassland.

No abstract

Severely disturbed habitats such as military training grounds, gravel pits and sand pits contribute to the species diversity of the agricultural landscape in Europe. They host a number of red-listed species not found elsewhere, illustrating that many plant species are threatened by extinction due to too little soil disturbance. Implementing a suitable disturbance regime is therefore crucial to ensure species-rich environments. We have reviewed the literature on soil disturbance as a restoration measure in dry sandy grasslands, with a special focus on xeric sand calcareous grasslands as these are severely threatened. Our objective was to elucidate the relations between diversity and disturbance regimes, and to determine how disturbance can be used to counteract acidification, to reduce nutrient availability and to create gaps in the vegetation. Our findings indicate that the current disturbance regime should be based on the historical disturbance regime, the productivity of the habitat and the propagule supply, in order to promote diversity at a landscape scale. Based on earlier studies and on the diversity/disturbance theory, we propose a conceptual model that can be used to determine the appropriate soil disturbance regime for restoration purposes. Our analysis highlights the importance of considering soil productivity, soil chemistry and dispersal limitations when choosing restoration measures and disturbance regimes for the conservation of biodiversity.

No abstract