Chaos belowground - 454 sequencing reveals strong priority effects and high resilience within arbuscular mycorrhizal fungal communities following disturbance

Summary 1. Differences in life-history strategies have been shown to drive the abundance of plant species in various environments, but whether or not similar processes operate on associated soil microbial communities is less known. Based on the assumed trade-off between disturbance tolerance and competiveness, we hypothesized that a severe disturbance applied within a semi-natural grassland would shift the arbuscular mycorrhizal (AM) fungal community from dominant competitive fungi to fungi that are normally rare and possibly disturbance tolerant. 2. We used 454-sequencing of the large subunit rDNA region to characterize fungal communities in Plantago lanceolata grown in the field for four months and exposed to no disturbance, or severe disturbance where fungi from undisturbed soil were either allowed or prevented from re-colonizing the disturbed area. To identify the AM fungi that could potentially colonize the experimental plants, we also analyzed roots from adjacent, undisturbed vegetation. 3. We found 31 fungal operational taxonomic units (OTUs) distributed across five fungal families. Contrary to our expectations, disturbance did not significantly alter the community composition. Instead, OTU abundances were positively correlated across treatments; i.e. OTUs that were common in undisturbed soil were also common after the severe disturbance, which suggests a high resilience of resident fungi. However, the distribution of OTUs within and between plots was largely unpredictable and could only to a small extent be explained by differences in plant community composition. Instead, pair-wise scatter plots showed that the four most abundant OTUs were seldom abundant in the same sample, which could be indicative of competition. 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 fungal communities after disturbance in this grassland appeared to be driven by small-scale spatial distributions and strong priority effects among AM fungi possessing a similar – and high – degree of disturbance tolerance. Key-words: Arbuscular mycorrhizal fungi, community composition, disturbance, life history strategy, 454 sequencing, semi-natural grassland.