Convergent shifts in soil fungal communities associated with Fagaceae reforestation in the Southern Appalachian Mountains

Forests of the Southern Appalachian Mountains were historically dominated by hardwood species within the family Fagaceae, e.g., American chestnut (Castanea dentata) and white oak (Quercus alba) among others. Due to numerous biotic and abiotic stressors, including pathogen pressure, populations of many Fagaceae have been greatly reduced, or functionally eliminated as is the case with American chestnut. This has led to reforestation efforts designed to increase American chestnut and white oak populations in this region, but success has been minimal. Since soil fungal communities are crucial to plant health, understanding how reforestation efforts alter soil fungal communities will inform reforestation efforts. Here, using nursery-reared bareroot seedlings of American chestnut, Chinese chestnut, 3rd generation backcross chestnut hybrids (BC3F3), and white oaks outplanted at a locally xeric site in the Southern Appalachian Mountains, we investigated if and how these species and backcross families within species differentially impact soil fungal communities. We demonstrate that after three years of growth, plant-associated soil fungal communities change similarly among different Fagaceae and are distinct from pre-planting soil communities. Interestingly, we observed differential shifts in fungal functional guilds among the Fagaceae species, although these were rather minimal. Taken together, the largely convergent shifts in soil communities across Fagaceae species suggest that these tree species may have similar impacts on soils and/or share similar communities that become enriched in closely related fungal species. The similarity in shared mutualist fungal communities suggests that companion planting or reforestation of genetically disease resistant American chestnut adjacent to establishing white oak trees might enhance survival and growth of both species at xeric sites.