Plant community reassembly on restored semi-natural grasslands lags behind the assembly of the arbuscular mycorrhizal fungal communities

The emerging plant communities on restored semi-natural grasslands are generally species poor subsets of the ancient target communities. Soil inoculation experiments suggest that the lack of suitable microbial communities, and especially of Arbuscular Mycorrhizal Fungi (AMF), may contribute to the low restoration success. To understand the limiting role that AMF play in mediating plant community assembly, we used pyrosequencing to investigate how entire AMF communities vary along a restoration gradient, covering 53 semi-natural grasslands in the Belgian Calestienne region. Soil AMF taxon richness, diversity and community composition of grasslands restored between 12 and 20 years ago were not different from the ancient grassland target communities, but strongly deviated from afforested grasslands. Yet, some AMF taxa exclusively occurred in ancient grasslands. Soil AMF communities were highly nested, with AMF communities from afforested grasslands and the youngest restoration stages being subsets of the older restoration stages and ancient grasslands. AMF communities in the roots of two grassland species were large subsets of the AMF communities retrieved from the soil and showed no host specificity. Plant community reassembly on the same grasslands strongly lagged behind the assembly of the AMF communities. Our results suggest low dispersal limitation of AMF, and indicate that AMF communities do not follow changes in the plant community. From a restoration management perspective, our results show that AMF communities reassemble within a reasonable time frame, and that the success of the manual introduction of target species in restored grasslands will likely not be limited by the absence of AMF.