Chisato Takenaka

Distribution of cesium-137 in Japanese forest soils: correlation with the contents of organic carbon

The spatial and vertical distributions of 137Cs in surface soils were surveyed and analyzed then correlated with the contents of organic carbon in the hinoki (Chamaecyparis obtusa Sieb. et Zucc.) plantation forest and secondary forest dominated by red pine (Pinus densiflora Sieb. et Zucc.) in Japan. The spatial variation of 137Cs activity was observed in the surface soil around the red pine. The average activity of 16 samples around the tree is 42.4 Bq/kg and the standard deviation is 25.9 Bq/kg. This finding indicates the importance in the selection of a sampling site and the number of samples from the surface soils especially around a tree. For the vertical distribution of 137Cs activity, it was found that the concentration in the surface soil is highest, 149 Bq/kg in the hinoki stand and 101 Bq/kg in the red pine stand, and decreases with depth. The relationship between 137Cs activity and carbon content in the forest soil was investigated in two undisturbed forest stands. The relations were more precisely expressed using an exponential equation than by a linear equation. From the same forest, similar regression equations were obtained. This indicates that the distribution of 137Cs could be characterized by the organic carbon content in an undisturbed forest. It is also suggested that the coefficient values in the regression equation help to define the movement of 137Cs accompanying the decomposition of organic matter.

Field Note: Arabis gemmifera is a Hyperaccumulator of Cd and Zn

Hyperaccumulators are essential for phytoremediation of heavy metals. In Europe and North America, many studies have been conducted to find more effective plants for phytoremediation of various pollutants. In Japan, this field of research has just recently come more into focus. A type of fern in Japan, Athyrium yokoscense, is well known as a hyperaccumulator of Cd and Zn. However, it is not suitable for phytoremediation because it is a summer green and grows slowly. Therefore, in order to find hyperaccumulators other than from A. yokoscense, we surveyed plants growing at polluted sites in Japan. We found that the Brassicae Arabis gemmifera is a hyperaccumulator of Cd and Zn, with phytoextraction capacities almost equal to Thlaspi caerulescens.

Growth of ternary InxGa1−xAs bulk crystals with a uniform composition through supply of GaAs

Ternary In0.14Ga0.86As bulk crystals with a uniform composition were found to be grown at a constant temperature by continuously supplying the depleted solute elements of Ga and As to the growth melt. The pseudo-binary InAs-GaAs melts were used as the growth melts. Compositionally graded 〈111B〉 InxGa1−xAs (0.05 ≤ x ≤ 0.08) crystals were used as seed crystals. The liquid encapsulated Czochralski (LEC) technique with a method of supplying GaAs source material was used to grow the ternary bulk crystals. Polycrystalline GaAs was used as a source material. A 4 mm thick and uniform In0.14Ga0.86As single crystal was obtained.

Methane flux and regulatory variables in soils of three equal-aged Japanese cypress (Chamaecyparis obtusa) forests in central Japan

To compare factors that control methane flux in forest soils, we studied three equal-aged Japanese cypress (Chamaecyparis obtusa) forests in Chubu district, central Japan. The three sites are located at different altitudes: 630 m (SET), 1010 m (INB), and 1350 m (OSK). Methane was absorbed at every site. The highest uptake rate was observed in the middle-altitude soil (INB, 5.89 mg CH4 m−2 d−1), which was the only site where methane uptake rate was correlated with air and soil surface temperatures. Methane flux in the field was not correlated with water content, inorganic N content, or water-soluble organic carbon. C/N ratio was correlated with methane flux (r=0.64,p<0.001). The results suggest that some organic inhibitors might be produced through decomposition of organic matter. There was a negative correlation between methane uptake rate and water-soluble Al (r=−0.63,p<0.001). Inhibition of methane consumption by 1 and 5 mM Al solutions was observed in laboratory incubation. This result suggests that water-soluble Al may be a factor controlling methane uptake. Multiple regression with a backward-elimination procedure identified three variables that were significantly associated with methane flux in the field (p<0.05): air temperature, C/N ratio, and the concentration of water-soluble Al.

Effects of aluminum stress on photosynthesis of Quercus glauca Thumb

In order to investigate the effects on photosynthesis of the aluminum (Al) and concentration and the calcium/aluminum (Ca/Al) ratio in the root environment of Quercus glauca Thumb, three-year-old seedlings were exposed to various nutrient solutions containing Al at two concentration levels (5 and 10 mM) with three Ca/Al ratios (5.0, 1.0 and 0.16). Exposure to the nutrient solution, in which the Al concentration was 10 mM (Ca/Al=0.16), limited photosynthesis and caused a decrease in stomatal conductance. The 5 mM Al treatments did not affect photosynthesis, even when the Ca/Al ratio was 0.16. The results of chlorophyll fluorescence and chlorophyll content, which showed no significant differences among the treatments, indicated that the Al treatments had no effect on photochemical processes. This means that the observed photosynthesis limitation would be due to stomatal closure and a decrease in the carbon dioxide fixation process. All Al-treated seedlings had increased leaf Al contents, decreased leaf phosphorus (P) contents and decreased water absorption ability in the roots. These results indicate that the Al treatments also affected nutrient availability, and function of the roots. However, since the effect on photosynthesis was observed only with the 10 mM treatment, this suggests that the effect of Al on root function is not directly related to the decrease in photosynthesis.

LEC growth of InGaAs bulk crystal fed with a GaAs source

Abstract In x Ga 1− x As ( x = 0.055 ± 0.004) bulk single crystals were grown by LEC while being fed with a GaAs source. To control the diameter and composition, a new crucible consisting of two melt reservoirs was used. The InGaAs crystal was grown in one melt reservoir and the source material was immersed in another reservoir. We confirmed that a homogeneous crystal with larger diameter than that of the seed can be obtained by growing at a constant temperature while dissolving sufficient GaAs source in the melt solution.

Growth of ternary In0.14Ga0.86As bulk crystal with uniform composition at constant temperature through GaAs supply

In using the liquid encapsulated Czochralski (LEC) technique, ternary In0.14Ga0.86As bulk crystals with uniform composition were grown at a constant temperature by successively supplying GaAs of the depleted solute component to the growth melt. The LEC technique with a supplying mechanism of GaAs source material was used to grow the ternary bulk crystal. A 4 mm long single bulk In0.14Ga0.86As crystal was obtained. Compositionally graded InxGa1-xAs (0.05<x<0.08) crystals were used as seed crystals. The seed crystals were prepared by using conventional LEC growth in which both the cooling rate and the pulling speed were optimized.

Reduction of dislocations in InGaAs layer on GaAs using epitaxial lateral overgrowth

Using liquid phase epitaxy (LPE), we grew an InxGa1−xAs layer (x ≤ 0.04) on a (111)B GaAs substrate using epitaxial lateral overgrowth (ELO), and studied the effects of ELO on reducing dislocations in mismatched heteroepitaxy. From observing etch pits corresponding to dislocations in the ELO layer, we found that ELO was effective in reducing the etch pit density (EPD) on mismatched heteroepitaxial layers. The largest reduction was obtained for a seed oriented in the 〈110〉 direction. We considered the reason for the EPD dependence on the direction of the seed to be as follows. Most of the etch pits in the ELO layers are caused by the propagation of misfit dislocations generated in the layer grown on the seed. For a seed in the 〈110〉 direction, along which misfit dislocations propagate, a large amount of strain energy was released by the dislocations propagating along the seed orientation. This causes the dislocations in the ELO layer to be suppressed.

Changes in chemical characteristics of surface soils in hinoki cypress (Chamaecyparis obtusa) forests induced by the invasion of exotic Moso bamboo (Phyllostachys pubescens) in central Japan

Invasion of contiguous forests by a giant bamboo (Moso bamboo, Phyllostachys pubescens) has the potential to induce changes in the chemical characteristics of soils due to the high growth rate of this species. We evaluated the impact of bamboo invasion into hinoki cypress (Chamaecyparis obtusa) forests on soil properties under varying conditions of shoot density at three study sites (Kanpachi, Seto, and Noguchi) in central Japan. We established three successive quadrats along bamboo invasion (allotted to a bamboo stand, a mixed stand of bamboo and hinoki, and a hinoki stand) at every site. Then, we measured the density and basal area of bamboo and hinoki shoots. Surface soil was sampled from each quadrat to analyze pH, water content, and exchangeable cation contents. The values of soil pH were significantly higher in the mixed stands than the hinoki stands at all sites, showing positive correlations with exchangeable Ca contents in the soil. Exchangeable K and Mg contents in the soil of the mixed stand showed significant differences compared with the hinoki stand only in Seto, but these values in the mixed stand were similar to those in the bamboo stand. This characteristic is consistent with the invasion degree determined from the density ratio of living bamboo culms to living hinoki trunks: Seto > Kanpachi > Noguchi. We conclude that increases in the soil pH due to bamboo invasion into hinoki forests resulted in distinct and sensitive changes in the soil chemistry.

Upward mobilization of 137Cs in surface soils of Chamaecyparis obtusa Sieb. et Zucc. (hinoki) plantation in Japan

The use of 137Cs has recently been adopted to estimate erosion in hinoki plantations in Japan. However, there have been several reports of the upward mobilization of 137Cs in forest humus layers. In this study, the vertical distribution of 137Cs within the soil profile was measured in a hinoki plantation. In order to confirm the upward migration of 137Cs from mineral soil to fresh surface litter and to identify mechanisms of the transfer, changes in 137Cs specific activity in the contents of litterbags were examined in a hinoki plantation. A controlled laboratory experiment was also conducted to assess the effect of microbial activity on the upward migration of 137Cs. As a result, the higher 137Cs activities in the surface organic layer of a hinoki plantation than in fresh litter and the increasing 137Cs total content of litterbags with time demonstrated the upward mobilization of 137Cs from mineral soil to the surface organic layer. Physical movement of soil particles by raindrop splash was considered an important process in 137Cs upward migration. The results of our laboratory experiment indicate an influence from soil microbial activity on the upward mobilization of 137Cs. Thus, upward migration of 137Cs and constant litter removal by runoff may induce 137Cs loss from steep forested catchments and underestimation of the 137Cs inventory leading to the overestimation of soil redistribution rates.