Soil transfers from intact to disturbed boreal forests neither alter ectomycorrhizal fungal communities nor improve pine seedling performance

Forest disturbances can alter mycorrhizal fungal communities with consequences for subsequent plant establishment and growth. One possible mitigation strategy to promote forest recovery following disturbances is inoculation with soil from late-successional forests. However, whether these soil transfers change the composition of resident fungal communities and how seedling growth responds to such transfers is unknown. To test whether soil transfers can mitigate disturbance-mediated impacts on ectomycorrhizal fungal (EMF) communities, we transferred soils containing fungal inoculum collected from conspecific late-successional forests into stands disturbed by wildfire, mountain pine beetle outbreak, clear-cut logging or salvage logging. Afterward, lodgepole pine seeds were sown to measure germination, establishment and growth of seedlings, and to characterize root-associated and soil EMF communities by sequencing the ITS1 rDNA region. Despite evidence that soil inocula contained viable EMF communities, transfers did not impact the root-associated or soil EMF community composition, or seed germination, seedling establishment and growth. Resident EMF community composition remained unchanged upon transfers of fungi from late-stage successional forests, and disturbance type singularly explained the EMF community composition associated with roots and soils. Ectomycorrhizal fungal taxa typically associated with mature pine forests were particularly abundant on roots of seedlings growing in plots impacted by beetle outbreak, while 'early-stage' EMF taxa were associated with seedlings growing in wildfire and logging disturbances. Synthesis and applications. Following disturbances, soil and root-associated EMF exhibit high functional redundancy, as seedling performance did not vary with differences in EMF community composition across disturbance types. Our findings suggest that soil transfers are unlikely to be an effective strategy in these stands and may be better targeted to highly degraded forests. The presence and abundance of EMF in disturbed forests should be assessed before committing to soil transfers as part of restoration.