Root-Associated Fungal Communities of Different-Aged Silver Birch Stands Naturally Regenerated on Abandoned Farmland

Natural regeneration of forests on abandoned agricultural land represents a cost-effective and sustainable pathway for restoring ecosystem functions and enhancing biodiversity. Root-associated fungi can influence the success of forest regeneration, especially under harsh habitat conditions, and serve as indicators of ecosystem maturation. Therefore, this study analyzed root-associated fungal communities in four silver birch stands regenerated by self-sowing on post-agricultural land. Stand ages were 13–14, 14–19, 18–23, and 23–28 years. Community analysis was based on sequencing of the ITS1 region using the AVITI (Element Biosciences), and soil C, N, and C:N ratios were determined. Taxa richness differed among stands, both for exclusive taxa (4–28) and total taxa per stand (49–84), with higher richness ecorded in the older stands. Trophic structure and α-diversity remained stable across stands. Ordination revealed a distinct clustering of root-associated fungal communities among the four studied stands. Late-stage ectomycorrhizal taxa dominated the older sites, whereas soil chemistry showed no clear association with community structure. Differences in fungal community assembly were likely driven by inoculum availability, local microsite conditions, and stochastic processes. These findings indicate that fungal succession during passive forest restoration on post-agricultural land is characterized primarily by progressive turnover in community composition rather than increasing diversity, with stand development and local factors jointly shaping fungal community assembly.