14C ages and δ13C were examined for sclerotium grains to elucidate the characteristics of these grains distributed in forest soils. The ages of the grains from surface A horizons and buried A horizons were ca 100-200 bp and ca 300-1,200 bp, respectively. In comparison with humic acid extracts, the 14C ages were in the increasing order: humic acid fraction < humic acid Pg fraction < sclerotium grains. The δ13C values for sclerotium grains in surface A horizons and buried A horizons were approximately -31‰ to -28‰, and these values were approximately 2-4‰ smaller than those of humic acids and soils. The C content of the grains had a tendency to decrease with increasing 14C ages, while the C content of humic acid was constant with age. The 14C ages of sclerotium grains indicate the individual age of grain formation, which are more likely to assign closer ages to the beginning of soil forming than the 14C ages of humic acid. The low δ13C values for sclerotium grains have presumably originated from characteristically biological organics, which may be protected from attack in soils because of their structure.
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