various fungi, including C. geophilum, to environmental stresses such as water stress
(Butler and Day 1998; Fernandez and Koide 2013). Melanin deposited in fungal cell
walls forms complexes with other cell wall components such as chitin, β-glucans,
and proteins (Butler and Day 1998). Most of the organic constituents of fungal cell
walls and sclerotia are believed to be labile compounds (Dallies et al. 1998). For
example, neutral saccharides account for 6.0–16% of the C content of C. geophilum
sclerotia collected from soil on Mount Ontake, central Japan (Sugiura et al. 2017).
Melanic tissues that directly colonize C. geophilum root tips, extramatrical mycelium, and sclerotia are likely to be large and stable pools of carbon in forest soils
(Dahlberg et al. 1997).
Sclerotia of Cenococcum geophilum can significantly contribute to the fungal
biomass of forest situations, and thus represent an important source of assimilated
carbon from host species (LoBuglio 1999). Vogt et al. (1981, 1982) estimated the
biomass of sclerotia in a 23- and 180-year-old Abies amabilis stand to be
2300 kg ha
À1 year
À1 and 3000 kg ha
À1 year
À1 , respectively. It is also known that
mycorrhizal root tips and sclerotia have their maximum production in autumn (e.g.,
Vogt et al. 1981, 1982; Lussenhop and Fogerl 1999). The existence of large
sclerotium grains (>5 mm) was noted by Kumada (1987) who collected the floating
grains in snow-melt streams of Asadaira (1500 m) Mt. Myoko, central Japan.
Although Cenococcum sclerotia can act as a substrate for diverse fungi (Obase
et al. 2014), they persist in forest soils for a long time. The facts give us a key
question “what are the Cenococcum sclerotia grains in soil?”
1.3 Sclerotia Grains in Earth Sciences Studies
Sclerotia-like grains may be able to be found in cultivated soils. According to
USDA/NRCS Soil Survey Manual (Soil Science Division Staff 2017), such grains
would be defined as concentrations; identifiable bodies within the soil that form and
accumulate due to pedogenesis. Pedogenic processes responsible for concentration
development in the soil include chemical dissolution and precipitation, oxidation/
reduction, and accrual due to physical or biological processes. Biological concentrations are discreet bodies accumulated by biological process, for example fecal
pellets and worm casts (Soil Science Division Staff 2017).
Sclerotia are rather studied in earth sciences; paleopedology, geochemistry,
sedimentology, and geology, with a different viewpoint from soil microbiology
and soil ecology. Sclerotia of Cenococcum geophilum, mainly, can be a resistant
marker of environmental archives, as both facies fossils and index fossils. Retallack
(1990) introduced fungal sclerotium, and/or sclerotinite, together with
spherosiderite, pyrite framboid, botryococcoid algal colony, which could be grouped
as some common constituents of coal and waterlogged paleosols. He also described
that some resting stages of fungi, sclerotia, are distinctive having small woody balls
with vermiform hollows common in peats and coals. The physical persistence of
vesicular-arbuscular mycorrhizal spores (grains of fungal products like sclerotia)
8
M. Watanabe et al.
(Butler and Day 1998; Fernandez and Koide 2013). Melanin deposited in fungal cell
walls forms complexes with other cell wall components such as chitin, β-glucans,
and proteins (Butler and Day 1998). Most of the organic constituents of fungal cell
walls and sclerotia are believed to be labile compounds (Dallies et al. 1998). For
example, neutral saccharides account for 6.0–16% of the C content of C. geophilum
sclerotia collected from soil on Mount Ontake, central Japan (Sugiura et al. 2017).
Melanic tissues that directly colonize C. geophilum root tips, extramatrical mycelium, and sclerotia are likely to be large and stable pools of carbon in forest soils
(Dahlberg et al. 1997).
Sclerotia of Cenococcum geophilum can significantly contribute to the fungal
biomass of forest situations, and thus represent an important source of assimilated
carbon from host species (LoBuglio 1999). Vogt et al. (1981, 1982) estimated the
biomass of sclerotia in a 23- and 180-year-old Abies amabilis stand to be
2300 kg ha
À1 year
À1 and 3000 kg ha
À1 year
À1 , respectively. It is also known that
mycorrhizal root tips and sclerotia have their maximum production in autumn (e.g.,
Vogt et al. 1981, 1982; Lussenhop and Fogerl 1999). The existence of large
sclerotium grains (>5 mm) was noted by Kumada (1987) who collected the floating
grains in snow-melt streams of Asadaira (1500 m) Mt. Myoko, central Japan.
Although Cenococcum sclerotia can act as a substrate for diverse fungi (Obase
et al. 2014), they persist in forest soils for a long time. The facts give us a key
question “what are the Cenococcum sclerotia grains in soil?”
1.3 Sclerotia Grains in Earth Sciences Studies
Sclerotia-like grains may be able to be found in cultivated soils. According to
USDA/NRCS Soil Survey Manual (Soil Science Division Staff 2017), such grains
would be defined as concentrations; identifiable bodies within the soil that form and
accumulate due to pedogenesis. Pedogenic processes responsible for concentration
development in the soil include chemical dissolution and precipitation, oxidation/
reduction, and accrual due to physical or biological processes. Biological concentrations are discreet bodies accumulated by biological process, for example fecal
pellets and worm casts (Soil Science Division Staff 2017).
Sclerotia are rather studied in earth sciences; paleopedology, geochemistry,
sedimentology, and geology, with a different viewpoint from soil microbiology
and soil ecology. Sclerotia of Cenococcum geophilum, mainly, can be a resistant
marker of environmental archives, as both facies fossils and index fossils. Retallack
(1990) introduced fungal sclerotium, and/or sclerotinite, together with
spherosiderite, pyrite framboid, botryococcoid algal colony, which could be grouped
as some common constituents of coal and waterlogged paleosols. He also described
that some resting stages of fungi, sclerotia, are distinctive having small woody balls
with vermiform hollows common in peats and coals. The physical persistence of
vesicular-arbuscular mycorrhizal spores (grains of fungal products like sclerotia)
8
M. Watanabe et al.