American chestnut (Castanea dentata) was eliminated as a canopy tree from the eastern forests of North America with the introduction of chestnut blight in the early 1900’s. Backcrossing, as a method of chestnut breeding resulted in progeny that display blight resistance. Current stripe-mine land reforestation projects provide ideal sites for chestnut re-establishment; i.e., low pH, full-sunlight, and relatively low competition. However, very little is known about the ectomycorrhizal (ECM) fungal communities present in severely disturbed mine sites that will form a symbiosis with chestnut seedlings. Further, it is not known whether these fungal partners will remain mutualistic to their plant symbionts when nutrients and organic matter are critically limited. This study characterized the ECM species that were found colonizing American chestnut and chestnut hybrid roots in mine reclamation projects. Site selection was analyzed to determine the environmental variables that may drive ECM species composition. Morphological characteristics coupled with the sequencing the ITS region was used to identify ECM in this study. Ordination techniques were used to determine differences in species composition against the environmental variables recorded among the sites. Lastly, growth parameters were compared to ascertain whether these ECM species were beneficial to their seedling hosts.
ECM diversity, community and subsequent host response of chestnut seedlings were recorded within three areas of a reclaimed mine site: forest edge, center, and with 10-year-old Pinus virginiana. Site selection influenced ECM diversity; seedlings planted with P. virginiana (0.66) and along the forest edge (.58) had a greater Simpson’s diversity index than the center plots (0.20) (P=0.03). Seedlings harvested from the Pine sites had fungal communities similar to those found along the forest edge. There was no difference in ECM species when comparing pure American chestnuts to the blight resistant hybrids. When determining environmental variables as drivers for ECM communities, pH and nutrient concentration tended to influence species composition. Eleven fungal genera were identified in this project. Of these, Scleroderma citrinum was the most abundant species found all the locations sampled in the study. EMC colonization resulted in significantly larger seedling biomasses (6.34 g) when compared to seedlings lacking an ECM symbiont (4.01 g) (P=0.005). This indicates that severely nutrient deficient sites harbor native ECM species capable of forming a symbiosis with chestnut resulting in a mutualistic relationship. Having an understanding of what environmental variables influence ECM communities may aid in proper site/tree selection used in future reclamation projects.