Mineral weathering in ectomycorrhizosphere of subalpine fir ( Abies lasiocarpa (Hook.) Nutt.) as revealed by soil solution composition

Abstract

The soil solution is considered an important index of nutrient availability, because it mimics the field conditions when plant roots obtained their nutrition, and reflects the weatherability of a particular soil mineral. The composition of soil solution is sensitive to physical, biological and chemical changes to soil systems, including the presence of fungal hyphae and rhizomorphs from ectomycorrhizal colonization. The objective of this paper is to compare the soil solution composition extracted from two ectomycorrhizosphere soils (or soil environment in the vicinity of ectomycorrhizae) to non-ectomycorrhizosphere soil of subalpine fir ( Abies lasiocarpa (Hook.) Nutt.) in the Ae horizon of Gray Luvisol in northern British Columbia. We extracted the soil solution from ectomycorrhizosphere of Piloderma spp. (ECS-A), Mycelium radicis atrovirens-cottony yellow-brown types (or where Piloderma spp. colonization was <2%) (ECS-B), and from non-ectomycorrhizosphere soils (N-ECM). These soils had been equilibrated anaerobically at field capacity for three weeks at room temperature. The content of major cations in solution, regardless of soil sample, followed the order Ca 2+ > K + > Mg 2+. We found that the concentrations as well as the activities of these cations followed the order ECS-A > ECS-B > N-ECM. A similar trend is true for K″, a parameter for the availability of soil K +. These trends are consistent to the results of geochemical models of more negative saturation index (or enhanced weathering) for muscovite, chlorite, anorthite and K-feldspars in ECS-A and ECS-B compared to N-ECM soils. Low pH in the ectomycorrhizosphere sample is believed to be responsible for the differential breakdown of soil minerals and the increased availability of K +, Ca 2+ and Mg 2+ in soil solution. The results from this study could have practical application in forestry, such as in use of fungal inoculation for improved survival of seedlings, especially in areas that shows deficiency of potassium and calcium.