Soil fungal communities in abandoned agricultural land has not yet moved towards the seminatural forest

The increasing trend in the abandonment of agricultural land provides a unique opportunity for the restoration of forests. However, not only vegetation but also belowground microbial communities are vital for the development of stable forest stands. To assess whether soil fungi can affect the succession of abandoned agricultural lands, we analyzed soil fungal communities, including total and arbuscular mycorrhizal (AM) fungi in agricultural lands (AG), short- and long-term abandoned agricultural lands (SA and LA), and short- and long-term regenerating seminatural forests (SR and LR). Vegetation analysis showed that the abandoned lands were gradually converting to seminatural forests. However, significantly lower soil pH values and higher C and N concentrations were found in the LR forests than in the other land use types. Although there were no significant differences observed in the total and AM fungal diversity among land use types, the species compositions of seminatural forests (LR and SR), abandoned lands (SA and LA), and agricultural land (AG) were clearly differentiated in the ordination analysis. Significant differences were observed between AG and other land use types and between LR and abandoned land in the case of total fungal communities. The ECM fungi associated with Alnus occurred on the LA plots, whereas the LR plots were characterized by different ECM fungi (Russula, Lactifluus) and a high abundance of ericoid fungi along with hygrocyboid and clavarioid taxa. These results indicate that fungal succession is not as straightforward as vegetation changes. AM fungi will probably not constrain the abandoned land succession towards seminatural forests, but total fungal communities could be hindered by soil properties and absence of host trees.