Birch leaf endophytes in managed and natural boreal forests

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Abstract
Fungal endophytes of birch trees are nonsystemic and transmitted horizontally by spores. Because the endophytes reinfect the leaves every growing season, the frequency of occurrence and species composition of the fungi depend on various abiotic and biotic environmental conditions. This was a study of possible effects of silviculture and local environmental variables on endophyte frequencies. Silver birch (Betula pendula Roth) leaves were sampled from seedling stands (five transects), managed mature forest (seven transects), and old natural forest (five transects) in the boreal vegetation zone in east-central Finland. The sapling stands had the highest endophyte frequency and the managed forest the lowest total infection frequency. The old natural forest tended to have the most diverse identified fungal species community, but the difference was not statistically significant. The most frequently isolated endophytic fungi were Fusicladium betulae (Rob. & Desm.) Aderh., consisting of 70% of the isolates from the sapling stands and 31% and 21% of the isolates from the managed forest and natural forest, respectively. It is probable that the sapling stands had plenty of available spores combined with an otherwise favourable microclimate. In the natural forests Gnomonia setacea (Pers.:Fr.) Ces. & de Not. was the most frequently isolated endophyte (30%), while in the sapling stands only 4% of the isolates belonged to G. setacea. In natural forest the frequency of G. setacea infections was positively correlated with stand age, indicating that G. setacea is favouring the old forest habitats.

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