Physicochemical characteristics of soil were investigated to clarify the effects of desalinization and plantation on salinity soil. Three plantation sites, which were desalinized by irrigation and planted trees 2 to 6 years ago, and two control sites were set in the mouth region of the Huang He River, China. The percentages of the large pores (under pF1.8),total carbon, nitrogen and exchangeable calcium concentration in upper soil (0-30cm)were higher in the plantation sites than in the control sites. In lower soil (30-60cm), soil hardness and pH in the plantation sites were higher than the control sites, and the pH values were over 8.5. The soil in the control sites was categorized into saline-sodic soil because the electric conductivity of saturated water (ECe) was 30-70mS/cm and the exchangeable sodium percentage (ESP) was 20%. In the plantation sites, ECe and ESP were 4mS/cm and 4-8%, respectively. Therefore, sodium was leached by cultivation and irrigation in the upper soil of the plantation sites that had a high rate of percolation. However, the soil pH and hardness increased in the lower soil of the plantation sites. In the plantation sites, the desalinization effect by irrigation was kept for at least 2 to 6 years and soil chemical properties were ameliorated by the low C/N ratio litterfall supply.

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In order to clarify the relationship between mangrove vegetation and site environments, topographical and phytosociological surveys were carried out along the two belt transects at the mouth of Sumiyo and Yakukachi Rivers in Amami-ohshima Island. Additionally, we established three study plots to estimate above-ground and below-ground stored carbon. The results of the phytosociological procedures yielded three communities, i.e. Kandelia candel community and Bruguiera gymnorrhiza community in the mangrove forests, and Heritiera littoralis community in the back mangrove forests. In the K. candel community, typical under community was found along the fringe of river, and B. gymnorrhiza under community was found on the delta. In the B. gymnorrhiza community, typical under community was found on the delta, and Excoecaria agallocha under community was found on the mounds of mud lobster in tidal zone. Heritiera littoralis community was found on the mounds above tidal zone. It was found that the distribution of communities have close correspondence with landform units in micro scale. The distribution range along water level of K. candel was lower than that of B. gymnorrhiza. Above-ground stored carbon of the K. candel forests was estimated to be 23.5±11.7tC/ha, which is 10 to 20% of tropical mangrove forests. Below-ground one up to 70cm in depth was estimated to be 104.0±7.1tC/ha, which is 20 to 30% of Rhizophora forests. This shows that K. candel has greater carbon strage ability on the forest floor as well as other mangrove species.

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Effect of soil acidification on the growth of Abies firma and its ectomycorrhizal status were examined. Plots treated with simulated acid rain were set at a 21-year-old stand of A. firma in the University Forest in Chichibu, The University of Tokyo. Acid rain treatments with sulfuric acid of pH 2 were monthly conducted on each plot from May to October for 6 years since 1994. In treated plots, pH of surface soil decreased from 6.5 to below 5.0, and surface soil contained less exchangeable K, Ca, and Mg but more exchangeable Al and Mn than control. Physiological activities of A. firma, such as water potential, chlorophyll fluorescence and photosynthetic rate, were not apparently different among treatments even in the end of 6th year. Ectomycorrhizal status changed drastically after the treatment. In treated plots, Cenococcum geophilum become dominant species, and number of ectomycorrhizal types decreased. Degree of ectomycorrhizal formation also decreased in treated plots. It is suggested ectomycorrhizal fungi is more sensitive to soil acidification than their host tree, A. firma.

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We compared the fruiting bodies of higher fungi at two sites with and without understory management. We surveyed fruiting bodies and forest settings in two 10×10-m plots and compared the percentages of fresh ectomycorrhizal (ECM) formation of Quercus serrata at both sites. The moisture of the soil at the unmanaged site was higher and the A_0 layer was thicker. Eleven species of ECM fungi were observed at the managed site along with five species of litter-decomposing fungi and two species of wood-decomposing fungi. In contrast, the unmanaged site had fruiting bodies belonging to two species of ECM fungi, five litter-decomposing fungi and five wood-decomposing fungi. Litter- and wood-decomposing fungi occurred regionally at the managed site, while ECM fungi occurred in the root sphere of ECM tree species, particularly in areas with high-relative photosynthetically active radiation (rPAR) -an index of lightness. The percentage of fresh ECM of Q. serrata was 52% at the managed site compared to 26% at the unmanaged site. These results suggest that ECM formation with fruiting bodies occurs more frequently at high-rPAR and low-organic-matter sites, whereas fruiting bodies of litter- and wood-decomposing fungi occur more frequently at high-organic-matter and high-moisture sites.

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[in Japanese]

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