Arocena,J.M. ad Glowa,K.R.(2000): Mineral weathering in ectomycorrhizosphere of subalpine fir (Abies lasiocarpa (Hook.) Nutt.) as revealed by soil solution composition. Forest Ecology and Management, 133, 61-70.


 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 Ca2+>K+>Mg2+. 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+, Ca2+ and Mg2+ 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.

Keywords: Ectomycorrhizospere soils; Ectomycorrhizae; Saturation index; Soil solution; Piloderma spp.; Mycelium radicis atrovirens (MRA)』

 土壌溶液は、植物根が栄養を得るときの野外条件に似ていることと、特定の土壌鉱物の風化しやすさを反映いていることのために、栄養分の利用しやすさの重要な指標と考えられる。土壌溶液の組成は、外生菌根のコロニー形成による菌糸と菌糸束の存在を含めて、土壌系に対する物理・生物・化学的変化に敏感である。本研究の目的は、ブリティッシュ=コロンビア州北部のGray LuvisolのAe層における亜高山性モミ(モミ属ミヤマバルサム)の、2つの外生菌根圏土壌(あるいは外生菌根周辺の土壌環境)から抽出された土壌溶液組成を、非外生菌根圏土壌と比較することである。我々は、Piloderma spp.(ECS-A)およびMycelium radicis atrovirens-cottony黄褐色型(あるいはPiloderma spp.のコロニー形成が<2%のところ)(ECS-B)の外生菌根圏からと、非外生菌根圏土壌(N-ECM)から土壌溶液を抽出した。これらの土壌は、室温で3週間、嫌気的に野外条件で平衡下におかれた。土壌試料に関係なく、溶液中の主要陽イオン含有量はCa2+>K+>Mg2+の順であった。これらの陽イオンの活動度はもちろん濃度はECS-A>ECS-B>N-ECMの順であることを、我々は見出した。同じ傾向が土壌の K+の利用しやすさの変数である K ''に当てはまる。これらの傾向は、N-ECM土壌に比べてECS-A と ECS-Bにおいて、白雲母・緑泥石・灰長石・カリ長石に対する大きな負の飽和指数(あるいは風化が進んだ)をもつという地球化学モデルの結果に一致する。外生菌根圏試料でpHが低いことは、土壌鉱物の異なる分解および土壌溶液のK+・Ca2+・Mg2+の利用しやすさの増加のせいであると思われる。本研究結果は、とくにカリウム・カルシウム不足を示す地域での、実生の生存を改良するための菌類接種の使用のような、森林における実用的な応用を可能にするだろう。』

1. Introduction
2. Materials and methods
 2.1. Description of the study area and sample collection
 2.2. Soil solution extraction and analyses
 2.3. Geochemical modeling and availability indexes
 2.4. Statistical analysis
3. Results
 3.1. Soil solution composition
 3.2. Stability of soil minerals
 3.3. Ionic strength, equilibrium pH, and availability of K+ and Ca2+
4. Discussion
5. Conclusions