Hoffland,E., Giesler,R., Jongmans,T. and van Breemen,N.(2002): Increasing feldspar tunneling by fungi across a north Sweden podzol chronosequence. Ecosystems, 5, 11-22.

 Tunnels in feldspar grains, assumed to be created by fungal hyphae, were first discovered in a boreal podzol. In this paper, we further describe the phenomenon of mineral tunneling by determining the rate of feldspar tunneling across a north Sweden podzol chronosequence. The chronosequence is a result of ongoing land uplift, which started after the retreat of glaciers about 9000 years ago. The sequence comprises a series of soils that began developing on glacial tills 190-7800 years ago. Feldspar tunneling was concentrated in the uppermost 2 cm of the E horizon, and its frequency increased significantly with soil age. Although no tunnels were found in feldspar grains from the youngest soil (190 years), they were seen more frequently in soils aged 2000 years and older. This lag phase in tunnel formation of about 2000 years coincided with the disappearance of the easily weatherable potassium-(K) and calcium (Ca)-containing minerals biotite and hornblende and with the appearance of etch pits on feldspar grains. In the oldest soil (7800 y), about 25% of the feldspar grains in the upper 2 cm of the E horizon were tunneled. Within site variation in tunnel frequency was high, and we were able to exclude spatial variations in mineralogy and texture as a possible explanation. The shape of the tunnels, their depth distribution, and the fungal hyphae found inside them all offer support for the previous assumption that their formation is mediated by biological activity involving fungi. The results of this investigation also indicate that the bioavailability of Ca and K may be a factor in tunnel formation.

Key words: weathering; feldspar; chronosequence; chronofunction; podzol; ectomycorrhiza; hornblende; Sweden; Ca and K biogeochemistry; micromorphology』


Study sites
 The soil chronosequence
 Profile descriptions
 Tunnel frequency
 Chemical weathering and soil formation
 Tunnel formation: Qualitative aspects
 Tunneling within a soil profile
 Tunnel frequency across the chronosequence
 Estimates of mineral tunneling
 Spatial variation
 Soil age and tunneling
 Lag phase
 Evaluation of the chronosequence

Figure 2. Thin-section micrographs in cross-polarized (A-G) and plain (H) visible light of plagioclase feldspars from Akerback(Aの頭に゜、aの頭に¨)(7800 y). A and B: Parallel-oriented, lens-shaped etch pits in a row, resulting in a sawtooth pattern. B also shows a single etch pit (upper left corner). C and D: Typical nonparallel pattern of feldspar tunneling. Tunnels show a constant diameter and a rounded end. E and F: Tunnel (t) formation at a mineral surface where etch pits (e) had been formed. G and H: Detail of a tunnel colonized by a fungal hypha. The septae of the hypha are clearly visible (H).


Figure 3. Scanning electon micrograph showing two fungal hyphae penetrating a feldspar grain.


〔『Hoffland,E., Giesler,R., Jongmans,T. and van Breemen,N.(2002): Increasing feldspar tunneling by fungi across a north Sweden podzol chronosequence. Ecosystems, 5, 11-22.』から〕

Figure 4. Percentage of tunneled feldspar grains as related to depth of mineral soil in Sor(oの頭に¨) Grundback(aの頭に¨) (6800 y). For each data point, 13 fields of view from a thin section (magnification ×100) were analyzed.

図4.Sor(oの頭に¨) Grundback(aの頭に¨) 産鉱物土壌(6800年前)の深さに関連づけた、穿孔のある長石粒子の百分率。各データ点について、1枚の薄片から13視野(倍率X100)が分析された。

Figure 5. Percentage of feldspar grains with tunnels in the first 2 cm of the E horizon. For each data point, 200 feldspar grains were considered. Five replicates per site were used. Some data points may be obscured by the overlap of markers. The solid line represents a fit (exponential increase) to all data (Y=0.87×10(0.000188X)-1). The dashed line represents a fit (exponential sigmoid) to the maximum values only for each site (Y=41/(1+e-(X-5874)/1585). r2 represents the percentage of variation statistically explained by soil age; n represents the number of observations considered; P <0.0001 in both cases.

図5.E層の最初の(最上部の)2cmにおける長石粒子の百分率。各データ点について、200の長石粒子が検討された。場所ごとに5試料が使われた。いくつかのデータ点は、記号の重複でわかりにくくなっている。実線はすべてのデータについての適合(指数関数的増加)を示す (Y=0.87×10(0.000188X)-1)。点線は各場所の最大値のみについての適合(指数関数的なS字状増加)を示す( Y=41/(1+e-(X-5874)/1585)。r2は土壌年代により説明される統計変動の百分率を示す;n は検討した観察数を示す;両者の場合とも P <0.0001。

〔『Hoffland,E., Giesler,R., Jongmans,T. and van Breemen,N.(2002): Increasing feldspar tunneling by fungi across a north Sweden podzol chronosequence. Ecosystems, 5, 11-22.』から〕