Chemical and mineral composition of ectomycorrhizosphere soils of subalpine fir (Abies lasiocarpa (Hook.) Nutt.) in the Ae horizon of a Luvisol

Differences in the properties of bulk forest and rhizosphere soils are often attributed to ectomycorrhizal association, or the symbiosis characterized by a fungal sheath surrounding the root (mantle) and intercellular root colonization (Hartig net). We compared the soil pH, total C, N, cation exchange capacity, and the contents of mica, chlorite, kaolinite, 2:1 expandable clays, feldspars and amorphous materials between two ectomycorrhizosphere soils (or soil environment in the vicinity of ectomycorrhizae (ECM)) and non-ectomycorrhizosphere soils to study the influence of ectomycorrhizae on chemical and mineralogical properties of soils. The two ectomycorrhizosphere soils were characterized by ectomycorrhizal colonizition dominated by (1) Piloderma spp., and (2) Mycelium radicis atrovirens and cottony yellow-brown (MRA-CYB) types or where Piloderma spp. colonization was <2%. Our results showed that total C and N were higher in ectomycorrhizosphere than non-ectomycorrhizosphere soils, and the ectomycorrhizosphere soils dominated by Piloderma spp. had almost twice the total C and N as ectomycorrhizosphere soils with MRA-CYB. Soil pH was lower by half a pH unit in ectomycorrhizosphere soils compared to non-ectomycorrhizosphere soils. Cation exchange capacity as well as exchangeable Ca2+, Mg2+ and K+ were lower in non-ectomycorrhizosphere soil compared to ectomycorrhizosphere soils. We also found that cation exchange capacity, exchangeable Ca2+, Mg2+ and K+ values in soils dominated by Piloderma spp. were higher compared to ectomycorrhizosphere soils with insignificant Piloderma spp. Our results suggest that transformation rate of mica and chlorite to 2:1 expandable clays was predominant in ectomycorrhizosphere compared to non-ectomycorrhizosphere soils, likely as a result of high production of organic acids and direct extraction of K+ and Mg2+ by fungal hyphae. In ectomycorrhizoplane samples, it is suggested that K+ and possibly amorphous Al2O3 and Fe2O3 could reconstitute the degraded mica and chlorite through the formation of hydroxy-interlayered 2:1 clays.