The Holocene vegetation history in south Sakhalin, east Asia, was reconstructed by means of pollen analysis and ^<14>C measurement for sediments obtained from four moors. Mixed forest composed mainly of Picea jezoensis and/or Picea glehnii, Abies sachalinensis, Betula and Alnus coexisting with Larix gmelinli, Pinus pumila, Quercus and Ulmus developed betwcen 〜4,600 yrBP and 300〜400 yrBP. The forest was characterised by the presence of L.gmelinii, which is the main component of the east Siberian conifer forest, and cool temperate trees such as Quercus and Ulmus. L. gmelinii increased in the moor at about 2,000 yrBP together with development of the highmoor. Quercus and Ulmus decreased markedly after 300-400 yrBP, and boreal forest of Picea, Abies, Larix, Pinus and Betula then flourished. An increase of coniferous trees occurred at 2,000 yrBP and 300-400 yrBP, and this was also recognized in the eastern part and the mountains of Hokkaido. This increase of conifers could have happened under cold climatic conditions. Tsuga pollen appeared between 3,000 and 3,800 yrBP in the moor along the Sea of Okhotsk. In Hokkaido, Tsuga pollen was also dated between 4,000 and 5,000 yrBP from the north and central coastal plain. Based on meteorological data from the northern limit of Tsuga diversifolia, Tsuga could become established along the Sea of Okhotsk coast of southern Sakhalin.
Transportation of phytoliths from major plants growing in the coastal zone were discussed based on the relationship between concentration in the surface sediments and the distance from the mother plant in several regions including Onneto, the estuary of the Mukawa River, Rokkasyo, the estuary of the Oirase River, Aiofutajima, and the estuary of the Obitsu River. The distribution of phytolith density for Phragmites type, Carex type and Calamagrostis type phytoliths indicated that they occurred at a high rate in the habitat of the mother plants. The densities of Leymus type and Imperata type phytoliths were higher inside rather than outside the growing area of the mother plants. Phytolith density in the sediments in relation to the coverage rate or the distance from the growth site suggested that the efficiency of transportation decreased in the order of "Phragmites type", "Carex type ・Ischaemum type ・Calamagrostis type" and "Leymus type・Imperata type" phytoliths.
Shoot morphology and growth characteristics of two morphologically similar submerged plants, Ranunculus nipponicus var. submersus and R. nipponicus var. okayamensis, were compared to clarify their morphological and ecological differences. Under both field and experimentally equalized conditions, these two plants were clearly distinguishable from each other on the basis of leaf and peduncle size by separating the reproductive and vegetative shoots, and also by leaf color during winter. Both plants showed continuous shoot growth in thc field, and seasonal change was higher for R. nipponicus var. okayamensis than for R. nipponicus var. submersus, possibly because of fluctuations of water temperature in the field. While the flowering of R. nipponicus var. submersus occurred all year round with a peak during June and July, that of R. nipponicus var. okayamensis was seen only during May and November. As to the effect of temperature on shoot growth, both plants showed thermophobic traits, and no significant difference. The elongation rate of R. nipponicus var. okayamensis was higher than that of R. nipponicus var. submersus in both of the water sampled from the Hongu River and the Utsumiya Rive, which are the natural habitats of R. nipponicus var. submersus and R. nipponicus var. okayamensis, respectively. The present results provide support for the suggestion that these two plants may be varieties rather than ecotypes.
Aiming to clarify the mechanism and prediction of CO2 exchange between a plant community and the atmosphere, a multilayer model of CO2 exchange having a feedback function is proposed. This model can calculate not only the profile of CO2 flux within and above a canopy, but also the profile of meteorological elements such as solar radiation, long-wave radiation, air temperature, specific humidity, wind velocity and CO2 concentration. The profiles are calculated using information on the canopy structure, leaf characteristics, and meteorological elements observed over the plant community. In order to validate the reproducibility of CO2 flux over the plant community by this model, we observed CO2, latent heat and sensible heat flux over aplanted forest, albedo and the profile of relative wind velocity, downward diffuse solar radiation and CO2 concentration within the canopy. By applying this model, we found that it could successfully reproduce not only CO2 flux, but also latent heat and sensible heat flux, over the canopy and reproduce the profile of these meteorological elements. Moreover, numerical experiments on CO2 flux were carried out using this model to investigate the influence of the characteristics of canopy structure on CO2 flux. As a result, we found the followings: (1) When the values of LAI arc 6 and 8, the fluctuations of CO2 fluxes over a canopy are more sensitive to the meteorological elements over the canopy than when the values are 1 and 3. (2) CO2 absorption by a community is not always greater during high solar elevation, as the average value of leaf inclination is greater. (3) Among the three canopies studied in the numerical experiments, one whose distribution of leaf area density is almost even absorbs CO2 gas the most.
The origins of H+ in forest ecosystem have hardly been discussed in Japan, although it is obvious that soil acidification includes not only anthropogenic processes such as acid deposition but also natural formation in the soil (pedogenesis). The concept of a H+ budget was used in a study of acid deposition in Sweden to evaluate the relative importance of H+ sources. The H+ budget can integrate most ionic nutrients, but mainly biogeochemical processes consisting of H+ production and consumption. To identify H+ sources and sinks, published data on nutrient cycling were reanalyzed in terms of H+ budget. Usually H+ production and consumption processes are heterogeneous in time and space; biochemical processes are active at the surface soil horizon, while at the deeper soil horizon geochemical processes like weathering predominate. For forest ecosystems, it is desirable to calculate the H+ budget for a watershed unit and the sepecific soil horizon. A distinct difference in H+ budget was found between Japan and European countries. In European forests, soil acidification is caused by external H+ input (acid deposition, especially SO2 and NH4+), whereas in Japanese forests, it is caused mainly by internal H+ production (cation uptake and nitrification in the surface soil horizon).