The Effects of Humidity and Seasonality on Foliar and Root Mycobiomes of Betula pendula

An increase in precipitation is predicted for Northern Europe over the coming century. In order to research how this change may affect fungi growing on Silver birch (Betula pendula), samples of its leaves and fine roots were collected over a 3-year period in the Free Air Humidity Manipulation experimental area in Estonia. Fungal DNA was extracted from the samples and sequenced to analyse the fungal communities. We found that increased air humidity shifts fungal community composition, but elevated soil irrigation does not. Variability in fungal communities caused by the experimental treatment was smaller than variability between sampling years and months. The response of species richness to elevated air humidity was inconsistent, whilst the proportion of saprotrophs and fungal endophytes increased. Analyses revealed that around 16% of all fungal species present in birch leaves avoided elevated air humidity, less than 2% preferred it. Fine root fungal communities appeared to be somewhat less influenced by changes in atmospheric humidity. Our results suggest that most of the foliar fungi are rather resilient to changes in atmospheric humidity, with a minority of species being sensitive to it, but the birch foliar fungal community as a whole does undergo a shift in composition.