Plant-soil interactions in American chestnut restoration
American chestnut has been functionally absent from Eastern U.S. forests for over half a century, resulting in altered tree community composition and soil properties. Hybrid blight-resistant American chestnut is likely to be reintroduced to Eastern forests within the next two decades, but it is unknown how it will perform in contemporary forests and how the forest community will respond to its introduction. Soil microbes, including those that are beneficial or antagonistic, can result in feedbacks that determine plant distribution and abundance. This plant-soil-feedback perspective is important in the context of terrestrial restoration. Our research sought to determine 1) which dominant tree species provide favorable soils for hybrid chestnut growth and 2) how dominant forest trees will subsequently respond to hybrid chestnut soils. We investigated the existence and strength of plant-soil feedbacks for chestnut, chestnut hybrids and current forest dominants (white oak, tulip poplar, and white pine). We conducted a fully reciprocal greenhouse experiment to examine the effects of species-specific soil inoculum on tree growth and mortality. Seedlings were grown in sterile matrix soil, inoculated with tree-specific soils collected from three southeastern forest sites (GA, NC and VA) and harvested after five months.
Tree growth was significantly affected by soil inoculum treatments. Chestnut growth was significantly lower in chestnut soil relative to other species’ soils. Mortality only occurred in hybrid and American chestnuts and was greatest for seedlings grown in their own soils. This finding suggests that chestnut-specific enemies accumulate in chestnut soils, which as a result, limit the capacity for their seedlings to survive and grow. Our findings also suggest that forests with abundant white oak, tulip poplar or white pine would be favorable locations for hybrid chestnut restoration efforts. American and hybrid chestnut had similar patterns in their response to soil treatments as well as the way in which their soils affected other species. This suggests that hybrids function similarly to American chestnut in below-ground community interactions. In hybrid soil, white oak growth was significantly greater than other species, suggesting that planting of hybrid chestnuts may promote white oak abundance in southeastern forests.