Landscape-scale variation in the canopy mycobiome in temperate beech and spruce forest stands explained by leaf water content and elevation

Fungi represent a significant portion of Earth's biological diversity and are essential for ecosystem functions like organic matter decomposition and nutrient cycling. While fungi associated with plant roots have been extensively studied, our understanding of fungi in the forest canopies remains limited. To investigate the landscape-scale variation in the canopy mycobiome of temperate beech and spruce forest stands in the Bavarian Forest National Park (Germany), we examined the influence of geophysical conditions and host traits. We found that elevation significantly influenced fungal diversity and composition, with distinct effects observed in both beech and spruce stands. Moreover, canopy water content, a key indicator of tree vitality, was also strongly associated with changes in the canopy fungi community, suggesting a potential link between forest water stress and the forest canopy mycobiome. Our differential abundance analysis further identified a total of 41 fungal families as potential bioindicators: 17 families in beech stands and 9 in spruce stands were significantly associated with elevation, while 9 families in beech stands and 6 in spruce stands were linked to variations in leaf water content. These findings enhance our understanding of the spatial patterns of forest canopy microbial biodiversity and species distributions