Fungal symbionts of bark and ambrosia beetles can suppress decomposition of pine sapwood by competing with wood-decay fungi

Bark and ambrosia beetles inoculate dying trees with symbiotic fungi. The effects of these fungi on wood decomposition are poorly understood. We determined the effects of three widespread Ascomycota symbionts and one introduced Basidiomycota symbiont on the decomposition of loblolly pine (Pinus taeda) sapwood. Ascomycetes caused <5% mass loss and no visible structural degradation, whereas the basidiomycete Flavodon ambrosius caused nearly 15% mass loss and visible structural degradation similar to free-living wood-decay fungi. Ophiostoma ips and Raffaelea fusca reduced white- and brown-rot decay through competition with Ganoderma curtisii and Phaeolus schweinitzii, respectively. The inhibitory effects of O. ips and R. fusca on decay were negated when co-inoculated with F. ambrosius suggesting that the spread of this invader could influence forest carbon cycles. In contrast to the predominant forest biology narrative, the common and widespread ophiostomatalean symbionts of bark and ambrosia beetles studied here appear to delay, rather than facilitate tree biomass recycling.