ferulic acid for growth but were not able to use naphthalene (a polycyclic aromatic
hydrocarbon). Furthermore, none of the representative strains showed acid tolerance
or grew at pH values below 4. Nonoyama et al. (2009) cultured bacteria strains,
including Ralstonia pickettii, Bradyrhizobium sp., Arthrobacter sp.,
Methylobacterium sp., Janibacter sp., and Nostocoida sp., that were found in
C. geophilum sclerotia collected from A horizon soil from the ONT profile. These
investigators experimentally measured reinvasion of the sterilized C. geophilum
sclerotia by the cultured bacterial strains and reported that the maximum count of
the R. pickettii strain was 8.7 Â 10
7 CFU/g sclerotia and that the fixing speed was
1.6 Â 10
6 CFU/h.
The results of these studies suggest that sclerotia cell structure and septal pores
provide habitat and entry pathways for bacteria, which may be responsible for
decomposition of the carbon in sclerotia. Additionally, ligninase enzymes extracted
from white rot fungi can degrade fungal melanin (Butler and Day 1998). As
previously mentioned, various parasitic fungal species may invade C. geophilum
sclerotia that persist in forest soil. Such fungi are often observed in the inner part of
C. geophilum sclerotia. The decrease in carbon content of sclerotia that we observed
suggests that the decomposition of sclerotia, especially the inner part, is due mainly
to microbial activity.
7.4 Conclusion
Sclerotia grains of C. geophilum in Japanese forest soils were characterized by AMS
14 C dating in comparison with soil humic acid and humin fractions. The
14 C ages of
sclerotia grains were older than those of humic acid extracts in equivalent soil
horizons. The
14
C ages of humic acids are more likely to indicate the mean age of
humus, whereas the
14 C ages of sclerotia grains indicate the age of formation of
individual grains. The older grains in soils may provide an estimate of the start of soil
formation or indicate the historical soil environment. The decrease in carbon content
of sclerotia grains suggested that decomposition or degeneration of carbon in the
grains is mainly due to internal microbial activity. The Al/C atomic ratio of sclerotia
grains, as determined by SEM-EDS analysis, showed a significant positive correlation with
14 C age, suggesting a possible indicator for age of sclerotia formation in
Andosols.
References
Benedict JB (2011) Sclerotia as indicators of mid-Holocene tree-limit altitude, Colorado Front
Range, USA. Holocene 21:1021–1023
Brunner I (2001) Ectomycorrhizas: their role in forest ecosystems under the impact of acidifying
pollutants. Perspect Plant Ecol Evol Syst 4:13–27
7 Dating of Sclerotia Grains in Andosol Profiles
135
hydrocarbon). Furthermore, none of the representative strains showed acid tolerance
or grew at pH values below 4. Nonoyama et al. (2009) cultured bacteria strains,
including Ralstonia pickettii, Bradyrhizobium sp., Arthrobacter sp.,
Methylobacterium sp., Janibacter sp., and Nostocoida sp., that were found in
C. geophilum sclerotia collected from A horizon soil from the ONT profile. These
investigators experimentally measured reinvasion of the sterilized C. geophilum
sclerotia by the cultured bacterial strains and reported that the maximum count of
the R. pickettii strain was 8.7 Â 10
7 CFU/g sclerotia and that the fixing speed was
1.6 Â 10
6 CFU/h.
The results of these studies suggest that sclerotia cell structure and septal pores
provide habitat and entry pathways for bacteria, which may be responsible for
decomposition of the carbon in sclerotia. Additionally, ligninase enzymes extracted
from white rot fungi can degrade fungal melanin (Butler and Day 1998). As
previously mentioned, various parasitic fungal species may invade C. geophilum
sclerotia that persist in forest soil. Such fungi are often observed in the inner part of
C. geophilum sclerotia. The decrease in carbon content of sclerotia that we observed
suggests that the decomposition of sclerotia, especially the inner part, is due mainly
to microbial activity.
7.4 Conclusion
Sclerotia grains of C. geophilum in Japanese forest soils were characterized by AMS
14 C dating in comparison with soil humic acid and humin fractions. The
14 C ages of
sclerotia grains were older than those of humic acid extracts in equivalent soil
horizons. The
14
C ages of humic acids are more likely to indicate the mean age of
humus, whereas the
14 C ages of sclerotia grains indicate the age of formation of
individual grains. The older grains in soils may provide an estimate of the start of soil
formation or indicate the historical soil environment. The decrease in carbon content
of sclerotia grains suggested that decomposition or degeneration of carbon in the
grains is mainly due to internal microbial activity. The Al/C atomic ratio of sclerotia
grains, as determined by SEM-EDS analysis, showed a significant positive correlation with
14 C age, suggesting a possible indicator for age of sclerotia formation in
Andosols.
References
Benedict JB (2011) Sclerotia as indicators of mid-Holocene tree-limit altitude, Colorado Front
Range, USA. Holocene 21:1021–1023
Brunner I (2001) Ectomycorrhizas: their role in forest ecosystems under the impact of acidifying
pollutants. Perspect Plant Ecol Evol Syst 4:13–27
7 Dating of Sclerotia Grains in Andosol Profiles
135