Mitsuhisa Baba

Calcium accumulation alleviates soil acidification in Japanese cedar (Cryptomeria japonica) stands

Abstract Larger amounts of exchangeable calcium (Ca2+) accumulated in the surface soil in an older Japanese cedar (Cryptomeria japonica) stand, compared with the younger stand. We estimated the Ca2+ accumulation rate and examined the difference in the amounts of exchangeable Ca2+ based on the Ca2+ fluxes. Samples of soil percolated water were taken using stainless tension-free lysimeters at different depths (under 0 horizon, 10,40, and 80 cm). Mobilization of base cations was controlled by total acid production. Proton load associated with N transformation was an important factor for the mobilization of base cations, especially for bivalent cations. Base cations tended to be mobilized in the 0 horizon and immobilized in soil horizons. The amount of Ca2+ supplied from the 0 horizon exceeded the amount recorded at the depth of 0–10 cm in the older Japanese cedar stand, resulting in the immobilization of 120 mmolc m−2 yr−1 of Ca2+ from October 2000 to September 2001. The amount of immobilized Ca2+ in the soil horizons in each period depended on the mobilized amounts in the 0 horizon. Lower amount of supplied Ca2+ in the 0 horizon and mobilization at the depth of 0–10 cm in the younger stand contributed to the difference in the amount of exchangeable Ca2+. Mobilization of base cations in the 0 horizon alleviated the loss of base cations in soil under Japanese cedar stands and contributed to the suppression of soil acidification.

Nitrogen Retention in Japanese Cedar Stands in Northern Honshu, with High Nitrogen Deposition

High nitrogen, especially ammonium, input has been observed in Shichinohe, Aomori Prefecture, northeastern Japan. A monitoring study on precipitation, throughfall, and stream water has been carried out to estimate the stage of nitrogen saturation since 19%. Fifty-two to 70 % of nitrogen input in throughfall was retained in forest ecosystems. Nitrate concentration in stream water tended to decrease throughout the study. There was no symptom of nitrogen saturation at Japanese cedar stands in Shichinohe, although high nitrogen input in open bulk has been observed. Ammonium (NH4+) was retained in the canopy. The ratio of NH4+ input in throughfall to that by open bulk was 0.40–0.47. Total inorganic nitrogen input under the canopy amounted 0.68–0.72 kmolc ha-1 yr-1 (9.6–10.0 kg N ha-1 yr-1). Our results suggests that atmospheric nitrogen input has benefitted the tree growth.

Changes in the quality of chromophoric dissolved organic matter leached from senescent leaf litter during the early decomposition.

Chromophoric dissolved organic matter (CDOM) leached from leaf litter is a major source of humus in mineral soil of forest ecosystems. While their functions and refractoriness depend on the physicochemical structure, there is little information on the quality of CDOM, especially for that leached in the very early stages of litter decomposition when a large amount of dissolved organic matter (DOM) is leached. This study aimed to better understand the variations/changes in the composition of CDOM leached from senescent leaf litter from two tree species during the early stage of decomposition. Leaf litter from a conifer tree (Japanese cedar, D. Don) and a deciduous broad-leaved tree (Konara oak, Thunb.) were incubated in columns using simulated rainfall events periodically for a total of 300 d at 20°C. The quality of CDOM was investigated based on the fluorescence properties by using a combination of excitation-emission matrix fluorescence (EEM) and parallel factor analysis (PARAFAC). In addition, the phenolic composition of DOM was investigated at a molecular level by thermally assisted hydrolysis and methylation-gas chromatography-mass spectrometry (THM-GC-MS) in the presence of tetramethylammonium hydroxide (TMAH). The EEM was statistically decomposed into eight fluorescence components (two tannin/peptide-like peaks, one protein-like peak, and five humic-like peaks). A significant contribution of tannin/peptide-like peaks was observed at the beginning of incubation, but these peaks decreased quickly and humic-like peaks increased within 1 mo of incubation. The composition of humic-like peaks was different between tree species and changed over the incubation period. Since tannin-derived phenolic compounds were detected in the DOM collected after 254 d of incubation on THM-GC-MS, it was suggested that tannins partially changed its structure, forming various humic-like peaks during the early decomposition.

Soil Solution Chemistry in Japanese Cedar Stands in Northern Honshu, with High Nitrogen Deposition

High nitrogen, especially ammonium, input has been observed in Shichinohe, Aomori Prefecture, northeastern Japan. The monitoring study on soil and soil solution has been carried out to determine soil acidification status since 1996. Soils and soil solutions in Minamitonai and Haginosawa are not strongly acidic. Fluctuations in nitrate concentrations coincided with sodium (Na+) or calcium (Ca2+). Produced protons due to nitrification were exchanged with Ca2+ or neutralized by weathering process. Exchangeable Ca2+ accumulated in surface layers, particular in the older Japanese cedar (Cryptomeria japonica) stand (42 years old). Exchangeable Ca2+ affected soil solution chemistry and the Ca2+ concentration was significantly higher in the older Japanese cedar stand than that in the younger stand (22 years old). Base cations, especially Ca2+, accumulation prevented soil (solution) acidification in Shichinohe site.

Determination of Iodide, Iodate and Total Iodine in Natural Water Samples by HPLC with Amperometric and Spectrophotometric Detection, and Off-line UV Irradiation

We developed a rapid, simple method for the iodine speciation analysis of water and applied it to natural water samples. Simultaneous determinations of I(-) and IO3(-) were achieved with an HPLC system with amperometric detection for I(-) and spectrophotometric detection after a postcolumn reaction for IO3(-). We determined the I(-) and IO3(-) concentrations in 20-μL water samples within 10 min. Total I concentrations in water samples were determined after the decomposition of organics by off-line UV irradiation for 30 min, followed by reduction to I(-). The analytical conditions were optimized by using test solutions rich in organic matter extracted from soils. We tested the new method with samples of groundwater, spring water, precipitation, soil percolate, stream water, and seawater as well as solutions extracted from soil. The method worked well, although the concentrations of some I species were below detection. This method is suitable for routine speciation analysis, which is important for studies of I behavior in the environment.