Bark beetle-fungal mutualisms and their effect on tree nutrient allocation, fungal diversity, and decomposition

Warming temperatures and drought have increased the extent and frequency of bark beetle outbreaks worldwide, with notable effects on forest ecosystems. When bark beetles colonize trees, they also introduce their own suite of associated fungi into host tissues. These fungal symbionts may aid beetles by translocating nutrients to the phloem where it is accessible for beetle larvae, but perhaps less accessible to fungal decomposers. To evaluate the extent to which bark beetles and their fungal symbionts influence nutrient allocation and fungal decomposer composition and richness, healthy Pinus ponderosa were felled, and logs made either accessible or inaccessible to beetles, and then monitored up to a year after initial colonization. In bark beetle colonized logs, nutrients were enriched in phloem tissues and depleted in the sapwood compared to control logs. This coincided with a shift in fungal community composition in sapwood that persisted up to a year after beetle establishment. These differences were driven by a greater abundance of soft rot fungi but a lower abundance of white rot fungi in beetle colonized logs, which may have implications on future decomposition rates and nutrient turnover in forests.