Root Response of Mature Live Oaks in Coastal South Carolina to Root Zone Inoculations with Ectomycorrhizal Fungal Inoculants

New fine root growth and ectomycorrhizal development were determined for mature live oak {Quercus virginiana) growing in a stressed landscape after soil injection of ectomycorrhizal fungal {Pisolithus tinctorius Pt) spores with or without fertilizer (12-48-8) or after vertical mulch application of a mix of Pt spores, soil-enriching bacteria, various organics, and water-managing gels. After 6 months, the injected spores stimulated more ectomycorrhizal development than the fertilizer or water-only control treatments. When spores and fertilizer were applied together, they increased by four times the fine root biomass and by three times the ectomycorrhizal development than observed in the water-only control. The estimated relative root absorbing potential of the roots was 14 times that of the control. After 4 or 6 months, the vertical mulch treatment stimulated six times more fine roots and twice the ectomycorrhizal development found in the control treatment. These differences reflected an 8 to 12 fold increase in the relative root absorbing potential of the fine roots and ectomycorrhizae. In both studies, Pt ectomycorrhizae accounted for over half of the ectomycorrhizal development. Natural ectomycorrhizal development ranged from 18 to 38 % of fine roots in control treatments. The results demonstrated that Pt spore and bacterial inoculants can be successfully introduced into the root system of mature live oaks in a stressed environment, increase fine root growth, and form abundant ectomycorrhizae.