It can be said that sclerotia grains are hardly recognized as soil constituents by soil
scientists, except Kumada who was the pioneer scholar introducing Cg sclerotia as
an origin of Pg, the green soil pigment. Comparative soil humus chemistry
highlighted C. geophilum sclerotia. Kumada and Hurst (1967) examined British,
Japanese and Swedish Podzols and showed that the presence of sclerotia (mean
diameter 0.5Æ0.4 mm in British Podzols; 1.1Æ0.4 mm in Japanese and Swedish
Podzols) in horizons A and B. Their interest to sclerotia came up with their
suggestion that the source of the green fraction of P type soil humic acid, so-called
“Pg,” derives from fungal metabolites and the skeletal formula of Pg was assumed as
DHPQ, dihydroxyperylenequinone 4,9-Dihydroxyperylene-3,10-dione. Various
quinone compounds are found in soil and sediment and known to be metabolites
of higher plants, soil fungi and lichens. Kumada and Hurst (1967) reported that P
type humic acid commonly present in podzolic soils and alpine grassland soils had
characteristic absorption band resulting from the presence of green pigment. Furthermore, it was suggested that the source of Pg was small spherical black fungal
sclerotia and this fungal species was tentatively identified as Cenococcum
graniforme (currently Cenococcum geophilum from their morphological
characteristics).
Approximately 50 years after the Kumada’s assumption, C. geophilum sclerotia
have become geochemist’s interest, to discuss the origin of Perylene. Perylene
(Perilene), a polycyclic aromatic hydrocarbon (PAH) displays blue fluorescence
under a UV light. In 1967, almost half a century ago from now, perylene was
found in sediments along the California coast. Later, many researchers found
perylene in the sediments of the ocean and lake around the world, but no one was
able to explain where this perylene came from.
Occasionally, a small blackish grain was observed in the sediment collected from
the bottom of the Lake Biwa, Central Japan (Itoh et al. 2010). In this study, fresh
sclerotia grains in forest soils of the catchment area of Lake Biwa were collected to
compare with the properties of the broken particles in sediment samples. By the
honeycomb cell structure and the existence of septal holes in each cell, the black
small grains from the Biwa lake sediment were identified as C. geophilum sclerotia.
In the next step, an experiment was designed to obtain the fluorescent spectra of
3 reagents, perylene, 3,10-perylene quinone, and dihydroxyperylenequinone with
the filter unit, and the observed and calculated spectra of each particle in different
diagenetic stages were compared. The good correspondence between the observed
and calculated spectra explained the transformation process of the particles. So, it
has become clear that Cg sclerotia are the possible origin of perylene. The sclerotia
grains produced in the forest soil of the catchment area flowed into Lake Biwa due to
runoff, and then over a long period of time after remaining on the lake bottom,
maybe not long, the chemical structure changed from DHPQ to perylene. At the
present time, Lake Biwa is the only case that confirmed the relationship between
sclerotia in forest soil and perylene in sediments. However, as with perylene and
sclerotia exist all around the world, there is the possibility that all the perylene in the
world is derived from DHPQ contained in sclerotia, the resting body of mycorrhizal
fungi.
10
M. Watanabe et al.
scientists, except Kumada who was the pioneer scholar introducing Cg sclerotia as
an origin of Pg, the green soil pigment. Comparative soil humus chemistry
highlighted C. geophilum sclerotia. Kumada and Hurst (1967) examined British,
Japanese and Swedish Podzols and showed that the presence of sclerotia (mean
diameter 0.5Æ0.4 mm in British Podzols; 1.1Æ0.4 mm in Japanese and Swedish
Podzols) in horizons A and B. Their interest to sclerotia came up with their
suggestion that the source of the green fraction of P type soil humic acid, so-called
“Pg,” derives from fungal metabolites and the skeletal formula of Pg was assumed as
DHPQ, dihydroxyperylenequinone 4,9-Dihydroxyperylene-3,10-dione. Various
quinone compounds are found in soil and sediment and known to be metabolites
of higher plants, soil fungi and lichens. Kumada and Hurst (1967) reported that P
type humic acid commonly present in podzolic soils and alpine grassland soils had
characteristic absorption band resulting from the presence of green pigment. Furthermore, it was suggested that the source of Pg was small spherical black fungal
sclerotia and this fungal species was tentatively identified as Cenococcum
graniforme (currently Cenococcum geophilum from their morphological
characteristics).
Approximately 50 years after the Kumada’s assumption, C. geophilum sclerotia
have become geochemist’s interest, to discuss the origin of Perylene. Perylene
(Perilene), a polycyclic aromatic hydrocarbon (PAH) displays blue fluorescence
under a UV light. In 1967, almost half a century ago from now, perylene was
found in sediments along the California coast. Later, many researchers found
perylene in the sediments of the ocean and lake around the world, but no one was
able to explain where this perylene came from.
Occasionally, a small blackish grain was observed in the sediment collected from
the bottom of the Lake Biwa, Central Japan (Itoh et al. 2010). In this study, fresh
sclerotia grains in forest soils of the catchment area of Lake Biwa were collected to
compare with the properties of the broken particles in sediment samples. By the
honeycomb cell structure and the existence of septal holes in each cell, the black
small grains from the Biwa lake sediment were identified as C. geophilum sclerotia.
In the next step, an experiment was designed to obtain the fluorescent spectra of
3 reagents, perylene, 3,10-perylene quinone, and dihydroxyperylenequinone with
the filter unit, and the observed and calculated spectra of each particle in different
diagenetic stages were compared. The good correspondence between the observed
and calculated spectra explained the transformation process of the particles. So, it
has become clear that Cg sclerotia are the possible origin of perylene. The sclerotia
grains produced in the forest soil of the catchment area flowed into Lake Biwa due to
runoff, and then over a long period of time after remaining on the lake bottom,
maybe not long, the chemical structure changed from DHPQ to perylene. At the
present time, Lake Biwa is the only case that confirmed the relationship between
sclerotia in forest soil and perylene in sediments. However, as with perylene and
sclerotia exist all around the world, there is the possibility that all the perylene in the
world is derived from DHPQ contained in sclerotia, the resting body of mycorrhizal
fungi.
10
M. Watanabe et al.