Local abiotic conditions are more important than landscape context for structuring arbuscular mycorrhizal fungal communities in the roots of a forest herb.

Due to human influence, large tracts of natural vegetation have been cleared and replaced by other types of land use, resulting in highly fragmented landscapes consisting of small fragments of well-conserved habitat scattered within a matrix of intensively managed land. Changes in land use and associated fragmentation have important consequences for biodiversity in the remaining fragments. Most studies so far have investigated the impact of land use change on macro-organisms, but little is known about how landscape fragmentation affects microbial communities. Here, we studied how changes in land use and abiotic conditions affected the arbuscular mycorrhizal fungal (AMF) communities in the roots of the forest herb Stachys sylvatica. Root samples were collected from 40 populations occurring in fragmented forest patches of varying age and size embedded within an agricultural landscape. Our results showed that forest age and isolation did not affect AMF diversity or community composition, suggesting that AMF disperse easily throughout the landscape and that AMF communities reassemble fast in recently established forest patches. On the other hand, AMF richness increased with increasing forest area, indicating that small forest sizes limit AMF richness. Additionally, AMF richness increased with increasing soil pH and decreased with soil nitrate content, while AMF community composition was affected plant-available phosphorus. Overall, these results show that landscape context is less important than local abiotic conditions for structuring AMF communities. However, the significant area effect indicates that further reductions in forest area will lead to impoverished AMF communities, potentially affecting long-term plant fitness and community structure.