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To determine the change in nutrient absorption capacity with stand development, we aimed to clarify the changes in fine root characteristics with stand development and stand characteristics...

Estimation of carbon sequestration in the forest sector should take into consideration changes in carbon stock in all carbon pools, including above-ground and below-ground biomass, litter, deadwood and soil. In this review, we discuss current knowledge of carbon stocks in litter, deadwood and soil in Japan’s forest sector. According to data from published reports and nationwide surveys, the carbon stock in forest litter is less than that indicated in the Intergovernmental Panel on Climate Change (IPCC) guidelines for temperate and cool temperate forests; for example, coniferous species showed 4.4 Mg C ha−1 for Cryptomeria japonica and 3.1 Mg C ha−1 for Chamaecyparis obtusa, and broad-leaved species ranged from 3.5 Mg C ha−1 for Castanopsis spp. to 7.3 Mg C ha−1 for Fagus spp. For deadwood carbon stock, coniferous plantations with a record of non-commercial thinning showed 17.1 Mg C ha−1 and semi-natural broad-leaved forests showed 5.3 Mg C ha−1 on average, although only limited data were availabl...

Soil CO2 production seasonality at a number of depths was investigated in a temperate forest in Japan and in a tropical montane forest in Thailand. The CO2 production rates were evaluated by examining differences in the estimated soil CO2 flux at adjacent depths. The temperate forest had clear temperature seasonality and only slight rainfall seasonality, whereas the tropical montane forest showed clear rainfall seasonality and only slight temperature seasonality. In the temperate forest, the pattern of seasonal variation in soil respiration was similar at all depths, except the deepest (0.65 m–), and respiration was greater in summer and less in winter. The contribution of the shallowest depth (around 0.1 m) was more than 50% of total soil-surface CO2 flux all year round, and the annual mean contribution was about 75%. CO2 production mostly appeared to increase with temperature in shallower layers. In contrast, in the tropical forest, soil CO2 production seasonality appeared to differ with depth. The CO2 production rate in the shallowest layer was high during the rainy season and low during the dry season. Soil CO2 production at greater depths (0.4 and 0.5 m–) showed the opposite seasonality to that in the shallower layer (around 0.1 m). As a result, the contribution from the shallow depth was greatest in the tropical forest during the rainy season (more than 90%), whereas it decreased during the dry season (about 50%). CO2 production appeared to be controlled by soil water at all depths, and the different ranges of water saturation seemed to cause the difference in seasonality at each depth. Our results suggest the importance of considering the vertical distribution of soil processes, particularly in areas where soil water is a dominant controller of soil respiration.

Soil CO2 levels reflect CO2 production and transport in soil and provide valuable information about soil CO2 dynamics. However, extracting information from soil CO2 profiles is often difficult because of the complexity of these profiles. In this study, we constructed a simple numerical model that simulated soil CO2 dynamics and performed sensitivity analyses for CO2 production rates, soil water content and temperature, and gas diffusivity at the soil surface to clarify the relationships among these parameters. Increased soil surface CO2 flux did not always coincide with higher soil CO2 concentrations; increased CO2 production at shallow depths had little effect on soil CO2 concentrations, while the opposite may be true for high levels of soil water content. Higher soil CO2 concentration did not always coincide with greater soil surface CO2 flux; under high soil water conditions, soil surface CO2 flux sometimes decreased despite increased soil CO2 concentration. Increases in soil water content did not always enhance both soil surface CO2 flux and soil CO2 concentration. Under high soil water conditions, increases in soil water content could lower soil surface CO2 flux and increase soil CO2 concentration. Increases in soil temperature resulted in greater soil surface CO2 flux and higher soil CO2 concentration in our simulation (extremely high temperatures were not assumed in this study). Gas diffusivity in very shallow layers did affect, albeit weakly, soil CO2 concentration. The findings of this study may help direct future observations and aid in the interpretation of their results.

Q10 is the most important index of soil respiration, and is essential for accurate prediction of soil carbon response to global warming. The response of soil carbon storage is an issue on global and regional scales. In this study, published Q10 values of soil respiration in Japanese forests were examined (n = 44). The Q10 values ranged from 1.30 to 3.45, and the mean value was 2.18 (SD = 0.61, median = 2.02). These results were slightly lower than those of global compilations. The number of studies of Q10 values is still lacking, especially with regard to those in managed forests, those in northeast Japan, and those using modern measurement techniques such as infrared gas analysis. For accurate prediction of soil carbon dynamics and storage in Japanese forests, more such studies are required.

Soil temperature is one of the most important factors governing biological activity in the soil. This study was conducted to investigate how forest clear-cutting changes soil temperature. Soil temperatures at 0.5, 1.0, 2.0, and 3.0 m depths were measured in two neighboring forest watersheds (35°12″N, 140°06″E) in Chiba Prefecture, Japan, from 1994 to 2000. One watershed was clear-cut 5 years after the observations began. After clear-cutting, the annual mean soil temperature at 0.5, 1.0, 2.0, and 3.0 m depths rose by about 2.2, 2.0, 1.7, and 1.4°C, respectively. The maximum respective soil temperatures rose by about 3.2, 3.0, 2.2, and 1.8°C. The minimum soil temperature rose slightly (≪1°C). The range of temperatures increased by 3.0, 2.4, 1.6, and 1.4°C, respectively. In our study, forest clear-cutting raised maximum and average soil temperatures but hardly changed minimum soil temperature. This is probably because solar radiation dominated in the summer season and increased soil temperature; on the other hand, net long-wave radiation, and releases of latent and sensible heat from the soil surface, were predominant in the cool season.

Soil respiration and soil carbon dioxide (CO2) concentration were investigated in a tropical monsoon forest in northern Thailand, from 1998 to 2000. Soil respiration was relatively high during the rainy season and low during the dry season, although interannual fluctuations were large. Soil moisture was widely different between the dry and wet seasons, while soil temperature changed little throughout the year. As a result, the rate of soil respiration is determined predominantly by soil moisture, not by soil temperature. The roughly estimated annual soil respiration rate was 2560 g C m−2 year−1. The soil CO2 concentration also increased in the rainy season and decreased in the dry season, and showed clearer seasonality than soil respiration did.

The real-time gas mass filter system consisting of a mass filter and a capillary sampling tube was developed for the analysis of products during electron beam (EB) irradiation of trichloroethylene (TCE)-air mixture. Interesting trace substances in gases are analyzed by this gas mass filter system in real time. The gases at atmospheric pressure are introduced to the mass filter under vacuum through a capillary tube without packing. The system was calibrated with three different standard mono-gases which contain known concentrations of sulfur dioxide, benzene and chlorobenzene for each. And its detectable limits for each gas were in the range of 0.7-1 ppmv. Products of irradiated TCE-air mixture were analyzed with the system in real time. The concentrations of dichloroacetyl chloride and carbonyl chloride (COCl 2 ) increased by low dose irradiation when TCE was decomposed. These products decreased by higher dose irradiation and were identified as primary products. Trichloroethylene and these primary products were oxidized into CO 2 , Cl 2 , and HCl at 15 kGy. Carbonyl chloride was dissolved in NaOHaq for natural-oxidation into CO 3 2- and Cl - . The doses for the complete oxidation of TCE and the products were decreased from 15 to 7 kGy by the combination of the irradiation and the dissolution of the irradiated gas. The decomposition mechanism of TCE, especially formation of COCl 2 , was clarified from the change of the products as a function of dose.

15P-water flow from the roots to the top in tomato (Lycopersicon esculentum Mill.) and rice (Oryza sativa L.) plants was visualized with time using a positron-emitting tracer imaging system (PETIS). The 15O-water flow was switched on by light and completely stopped in the dark. The flow rate in the stem of tomato and the shoot of rice at a light intensity of 500 μmol·m−2·s−1 was 1.9 and 0.4 cm min−1, respectively.

A new apparatus that determines the gas diffusion coefficient in soil after establishing steady state gas conditions was developed. The CO2 concentration is kept constant above and below the soil sample to establish the steady state conditions. The sample column is 60 cm long with an inner diameter of 20 cm. The gas diffusion coefficients of sandy soil were measured at 10 cm intervals using this apparatus while controlling the soil water content. The ratios of gas diffusion coefficients in soil and air,Ds/D0, with different soil water conditions were determined.

By considering trade-offs and complementarity between carbon removal from the atmosphere by forests and emission reduction by wood use, we developed a forest-sector carbon integrated model for Japan. We discuss mitigation measures for Japan based on model projections. The integrated model included the forest model and the wood use model. Based on three scenarios (baseline, moderate increase, and rapid increase) of harvesting and wood use, the integrated model projected mitigation effects including carbon removal by forests and emission reduction through the wider use of wood, until 2050. Results indicate that forests will not become a source of net carbon emissions under the three scenarios considered. The baseline scenario is most effective for mitigating climate change, for most periods. However, the sum total of carbon removal in forests and carbon emission reductions by wood use under the rapid increase scenario exceeded the one of the moderate increase scenario after 2043. This was because of strong mitigation activities: promoting replanting, using new high-yield varieties, and wood use. The results also indicated that increases in emission reduction due to greater wood use compensated for 67.9 % of the decrease of carbon removal in 2050, for the rapid increase scenario. The results show that carbon removal in forests is most important in the short term because of the relative youth of the planted forests in Japan, and that mitigation effects by material and energy substitution may become greater over the longer term.