Ectomycorrhizal (ECM) fungi form mutualistic symbioses with woody trees and shrubs allowing for an increase in water and nutrient uptake. The absence of these microbes may contribute to seedling mortality and the arrested succession observed in barren landscapes and grasslands in Ohio. The central objective of this dissertation was to develop planting methodologies to accelerate succession by woody tree establishment; specifically by maximizing the effectiveness of ECM root colonization. American chestnut and chestnut hybrids were used to describe host response to root colonization in both abandoned and reclaimed mine sites in central Ohio. A set of experiments was designed to test the influence existing vegetation, site selection, soil modification, and the addition of ECM inoculum may have on seedling establishment in former mine sites.
I investigated the influence existing vegetation had on germination and survival of chestnut in an abandoned mine site. Three areas were assessed: center, areas that had monoculture plantings of Pinus virginiana, and forest edges. Small monoculture plantings of pines had a greater facultative effect on the germination and survival of deciduous hardwood seedlings than did the forest edge; presumably by alleviating negative density-dependent factors. Importantly, pine and chestnut shared ECM symbionts. This provided an ECM propagule source to chestnut and resulted in an increase in seedling biomass, which may have contributed to the increase in survival after two years.
In reclaimed mines, heavy equipment and the use of exotic species as cover crops have resulted in severely compacted soils with aggressive herbaceous canopies. I evaluated surface soil treatments, which included deep ripping and traditional plow and disking, as ways to remediate these mine lands in arrested succession. These methods were very successful in alleviating compaction and disturbing the aggressive herbaceous canopy, thereby promoting chestnut seedling establishment. In addition, mechanical soil treatments resulted in seedlings with significantly more ECM root tips with greater species richness. Further, there was a significant interaction between soil treatment and ECM colonization. Chestnut seedlings naturally colonized by ECM fungi in treatment plots had the greatest shoot production when compared to their non-ECM counterparts.
I assessed the field performance of five different ECM fungi inoculated on hybrid chestnut. These ECM species did not persist on chestnut after one year in the field or impede natural root colonization of native fungi. However, the presence of ECM inoculum greatly contributed to the survival of hybrid chestnut seedlings. Therefore, introduced inoculum that was present in the very early stages of outplanting had persisting effects with regard to seedling development in the field, even if the original inoculum did not persist. Important to chestnut restoration was that native ECM fungi colonized chestnuts and resulted in an increase in seedling growth.
Soil variables and ECM community data were used to determine the influence the soil environment has on ECM community composition and root colonization of American chestnut. Differences in ECM communities were associated with differences in nutrient availability; this may have catalyzed a shift in fungal communities to species better able to persist in acidic soils under nutrient-limited conditions. In addition, certain species appeared not to exist as mycelium on existing vegetation, but have the ability to rapidly recruit after mechanical soil treatments. Results of this study help us better understand whether abiotic soil variables can be used to predict ECM composition and root colonization potential in mine restoration using blight-resistant chestnut hybrids.
Proper site selection and soil surface treatment methods significantly contributed to ECM root colonization on chestnut in abandoned and reclaimed mine sites in central Ohio. Employing methodologies that encourage the formation of native ectomycorrhizas may aid in promoting the long-term survival of woody tree species in mine reclamation and accelerate succession to closed canopy forests.