(JED-2300 Analysis Station with the ZAF method standardless quantitative analysis
program, JEOL).
SEM observation at a magnification of up to 100,000Â was used to examine the
morphology of the inner areas of the other halves of the sclerotia samples. Under an
optical microscope, powder samples were collected from the inner area of the
sclerotia with a sterilized needle. The powder samples were scattered on carbon
tape, coated with osmium, and analyzed with a thermal field emission scanning
electron microscope (JSM-7100F or 7800F, JEOL) equipped with an EDS
(JED-2300, JEOL), at an accelerating voltage of 5 kV. The data were analyzed by
means of the ZAF method standardless quantitative analysis program. The elemental
composition of the needle was also determined, to exclude the possibility of metal
contamination from the needle.
7.3.2 Results and Discussion
The soil properties are summarized in Table 7.1. The pH (H 2 O) and pH (KCl) ranges
of the surface soils of the three profiles were 3.9–5.2 and 3.1–3.7, respectively. The
pH (H 2 O) and pH (KCl) values of the subsurface soils were 4.2–5.3 and 3.5–4.5,
respectively. The TC content of surface soils ranged from 15% to 28% and 4.4% to
18% in subsurface soils. The buried A horizons (2A and 3A) of the MYK profile had
pH (H 2 O) and pH (KCl) ranges of 5.2–5.4 and 4.3–4.4, respectively. The TC
contents of the buried A horizons (2A and 3A) of the MYK profile were 7.9–9.2%.
The weights and numbers of sclerotia used for dating are summarized in
Table 7.2, along with the AMS
14 C ages. The
14 C ages (Libby age) of the sclerotia
from each ONT horizon were as follows: A1: 499–831 year BP, A2: 1134–1688 year BP, E: 1590–1897 year BP, and Bs: 2121–2720 year BP. The
14 C ages
of the sclerotia in the IWK profile were as follows: A1: modern (<50 year BP), A2:
125–228 year BP, BA: 951–1340 year BP, and Bw: 2620–2798 year BP. Among the
ONT sclerotia, larger grains tended to be older than smaller grains. There was no
clear relationship between age and size in the IWK sclerotia. Watanabe et al. (2007b)
reported the following ages for MYK sclerotia: 1A: 95–240 year BP, 2A: 305–1000 year BP, and 3A: 1020–1200 year BP. Among the younger MYK sclerotia
(<600 year BP, horizons 1A and 2A), age tended to increase with diameter, whereas
there was no clear relationship between age and size for sclerotia obtained from the
3A horizon (>1000 year BP).
Example of the elemental area analysis of the cell walls of the sliced section
samples is shown in Fig. 7.6. Overall, the carbon and oxygen content ranges were
55.9–67.6 wt% and 31.6–38.0 wt%, respectively. The ONT sclerotia contained
relatively large amounts of aluminum (1.20–5.89 wt%) and iron (1.44–5.71 wt%)
compared with the IWK and MYK sclerotia (aluminum: 0.20–4.34 wt%, iron:
0.36–1.52 wt%). The inner area of the IWK-A1 sclerotia (modern, as indicated by
132
M. Watanabe et al.
program, JEOL).
SEM observation at a magnification of up to 100,000Â was used to examine the
morphology of the inner areas of the other halves of the sclerotia samples. Under an
optical microscope, powder samples were collected from the inner area of the
sclerotia with a sterilized needle. The powder samples were scattered on carbon
tape, coated with osmium, and analyzed with a thermal field emission scanning
electron microscope (JSM-7100F or 7800F, JEOL) equipped with an EDS
(JED-2300, JEOL), at an accelerating voltage of 5 kV. The data were analyzed by
means of the ZAF method standardless quantitative analysis program. The elemental
composition of the needle was also determined, to exclude the possibility of metal
contamination from the needle.
7.3.2 Results and Discussion
The soil properties are summarized in Table 7.1. The pH (H 2 O) and pH (KCl) ranges
of the surface soils of the three profiles were 3.9–5.2 and 3.1–3.7, respectively. The
pH (H 2 O) and pH (KCl) values of the subsurface soils were 4.2–5.3 and 3.5–4.5,
respectively. The TC content of surface soils ranged from 15% to 28% and 4.4% to
18% in subsurface soils. The buried A horizons (2A and 3A) of the MYK profile had
pH (H 2 O) and pH (KCl) ranges of 5.2–5.4 and 4.3–4.4, respectively. The TC
contents of the buried A horizons (2A and 3A) of the MYK profile were 7.9–9.2%.
The weights and numbers of sclerotia used for dating are summarized in
Table 7.2, along with the AMS
14 C ages. The
14 C ages (Libby age) of the sclerotia
from each ONT horizon were as follows: A1: 499–831 year BP, A2: 1134–1688 year BP, E: 1590–1897 year BP, and Bs: 2121–2720 year BP. The
14 C ages
of the sclerotia in the IWK profile were as follows: A1: modern (<50 year BP), A2:
125–228 year BP, BA: 951–1340 year BP, and Bw: 2620–2798 year BP. Among the
ONT sclerotia, larger grains tended to be older than smaller grains. There was no
clear relationship between age and size in the IWK sclerotia. Watanabe et al. (2007b)
reported the following ages for MYK sclerotia: 1A: 95–240 year BP, 2A: 305–1000 year BP, and 3A: 1020–1200 year BP. Among the younger MYK sclerotia
(<600 year BP, horizons 1A and 2A), age tended to increase with diameter, whereas
there was no clear relationship between age and size for sclerotia obtained from the
3A horizon (>1000 year BP).
Example of the elemental area analysis of the cell walls of the sliced section
samples is shown in Fig. 7.6. Overall, the carbon and oxygen content ranges were
55.9–67.6 wt% and 31.6–38.0 wt%, respectively. The ONT sclerotia contained
relatively large amounts of aluminum (1.20–5.89 wt%) and iron (1.44–5.71 wt%)
compared with the IWK and MYK sclerotia (aluminum: 0.20–4.34 wt%, iron:
0.36–1.52 wt%). The inner area of the IWK-A1 sclerotia (modern, as indicated by
132
M. Watanabe et al.