Temporal and spatial shifts in the foliar fungal endophyte community of Norway spruce (Picea abies) over 150 years in Finland

Herbarium specimens are invaluable for studying plant. Yet their potential to reveal historical plant-associated microbiomes remains largely unexplored. To address this gap, we reconstructed the temporal and spatial dynamics of foliar fungal endophytes in Norway spruce ( Picea abies ) by sequencing the fungal internal transcribed spacer (ITS) region from herbarium needle specimens collected in Finland between 1861 and 2023. We analyzed community shifts across 50-year and 20-year intervals and between southern and northern regions, assessing the influence of temperature and precipitation. The results showed that the community was dominated by Ascomycota, with Lophodermium , Ceratocystis, Yarrowia , Saccharomyces , and basidiomycota Heterobasidion as the most abundant genera. Among the 50-year intervals, H. parviporum was detected, and the abundance of Lophodermium picea increased in 20-year interval (2001–2023, P  < 0.05). The fungal community composition differed significantly between the interval 1951–2000 and both 1851–1900 and 1901–1950 ( P  < 0.05). The southern region exhibited distinct fungal community and lower alpha diversity indices compared to the north ( P  < 0.05). Functional prediction revealed a significant increase in Saprotroph, Symbiotroph and Pathotroph-Saprotroph-Symbiotroph guilds in the 1901–1950 interval ( P  < 0.05). While temporal and spatial factors significantly structured the communities, no direct correlation with historical temperature or precipitation was found. Our findings demonstrate that herbarium specimens are a powerful resource for uncovering long-term microbial dynamics and highlight the primary roles of time and geography in shaping the foliar fungal microbiome.