The mycobiont community above the alpine forest line may act as a barrier to seedling establishment of Betula pubescens

Abstract

Climate change is affecting ecosystems worldwide. The northern hemisphere has experienced significant warming over the last decades, particularly strong in arctic and alpine ecosystems. Forests are predicted to migrate into these ecosystems as temperatures increase, although the predicted migration falls short of what is actually observed. In this study, I test the hypothesis that the soil fungal community above the tree- and forest line may act as a barrier to seedling establishment of Betula pubescens. I predict that the soil fungal community may lack the symbionts necessary for the plants to thrive, even if the temperature is suitable. I tested this hypothesis by collecting soil from two alpine areas above the forest line and two areas of semi-natural grasslands with natural populations of B. pubescens and compare the growth of seedlings in a common garden experiment. The seedlings were exposed to two different temperatures. After eleven weeks of growth the fungal communities in both soil and roots were analyzed using a metabarcoding approach. I found that B. pubescens grown in alpine soils associated with typical alpine mycorrhizal fungi, normally found in the roots of Ericaceous plants. These plants showed impaired growth compared to the plants growing in lowland soil. I found support for the hypothesis that the alpine fungal community may act as a biotic barrier for establishment of B. pubescens seedlings above the forest line.