Bark beetle infestation alters mycobiomes in wood, litter, and soil associated with Norway spruce

Recent exceptionally hot and dry summers provoked massive bark beetle outbreaks in German forests, which killed many conifers, forcing to clear-cut complete non-mature stands. The importance of fungi in ecosystems in particular in association with trees is widely recognized, but the ecology of how insect infestations of trees affect their mycobiomes remains poorly understood. Using Illumina MiSeq sequencing, we investigated fungal communities in soil, litter, and stem wood at early and late stages of bark beetle infestation in a Norway spruce [Picea abies (L.) Karst] stand in Central Germany. Fungal diversity decreased from soil to wood, with the highest proportion of unknown fungi in stem wood. Lifestyles, particularly of those fungi associated with stem wood, clearly changed depending on the infestation stage. The answer of tree-associated fungi to beetle infestation was characterized by an increasing community dissimilarity among all three habitats, i.e. it concerned not only the above-ground fungal communities directly connected to the tree. Our study, thus, pinpoints the cascading effects of tree infestations by bark beetles and subsequent tree diebacks on the proximate and distant mycobiomes of the plant soil system, which should be entirely considered to tackle the effects of environmental events on tree health.