To clarify the reason for the higher CH 4 uptake rate in Japanese forest soils, twenty-seven sites were established for CH 4 flux measurement. The first order rate constant for CH 4 uptake was also determined using soil core incubation at 14 sites. The CH 4 uptake rate had a seasonal fluctuation, high in summer and low in winter, and the rate correlated with soil temperature at 17 sites. The annual CH 4 uptake rates ranged from 2.7 to 24.8 kg CH 4 ha -1 y -1 (the average of these rates was 9.7 or 10.9 kg CH 4 ha -1 y -1 , depending on method of calculation), which is somewhat higher than the uptake rates reported in previous literature. The averaged CH 4 uptake rate correlated closely with the CH 4 oxidation rate of the topsoil (0-5 cm) in the study sites. The CH 4 oxidation constant of the topsoil was explained by a multiple regression model using total pore volume of the soil, nitrate content, and C/N ratio (p \ 0.05, R 2 = 0.684). This result and comparison with literature data suggest that the high CH 4 uptake rate in Japanese forest soils depends on the high porosity probably due to volcanic ash parent materials. According to our review of the literature, the CH 4 uptake rate in temperate forests in Europe is significantly different from that in Asia and North America. A new global CH 4 uptake rate in temperate forests was estimated to be 5.4 Tg y -1 (1 SE is 1.1 Tg y -1 ) on a continental basis.

No abstract

-The CO 2 fluxes from the forest floor were measured using a closed chamber method at 26 sites from 26 • N Lat. to 44 • N Lat. in Japan. Seasonal fluctuation in CO 2 flux was found to correlate exponentially with seasonal fluctuation in soil temperature at each site. Estimate of annual carbon emission from the forest floor ranged from 3.1 to 10.6 Mg C ha −1 . The emission rate of soil-organic-carbon-derived CO 2 , obtained by incubation of intact soil samples, correlated closely with the carboxymethylcellulase (CMCase) activity in the soil. The sum of cool-water soluble polysaccharides, hot-water soluble polysaccharides, hemicellulose, and cellulose content in the soil was greater at the sites with low CMCase activity than that at the sites with high CMCase activity. Because the sites in cooler-climate sites had a high content of easily decomposable soil organic carbon and organic litter, the potential increase in CO 2 efflux from forest floor with increasing soil temperature would be greater in cooler-climate sites.cellulose / Japanese forest / soil organic carbon / soil respiration Résumé -Fort potentiel d'accroissement de flux de CO 2 issu de la surface du sol forestier en relation avec le réchauffement global dans les régions fraîches du Japon. Le flux de CO 2 issu du sol forestier a été mesuré dans 26 sites, allant du 26 • au 44 • de latitude Nord dans l'archipel japonais, en utilisant la méthode des chambres fermées. Il a pu être mis en évidence que la fluctuation saisonnière du flux de CO 2 était corrélée de façon exponentielle avec celle de la température du sol de chacun des sites étudiés. L'estimation annelle de l'émission de carbone venant du sol variait de 3,1 à 10,6 Mg C ha −1 . Le taux d'émission de CO 2 obtenu par incubation d'échantillons intacts de sol est corrélé positivement avec l'activité de la carboxyméthacellulase (CMCase), dans le sol. La somme totale des polysaccharides solubles dans l'eau froide, des polysaccharides solubles dans l'eau chaude, des hémicelluloses et de la cellulose contenus dans le sol était plus grande dans les sites caractérisés par une faible activité CMCase que dans les sites avec une forte activité CMCase. Du fait que les sites en climat frais ont un contenu élevé en carbone organique du sol facilement décomposable et une litière organique, le potentiel d'accroissement du flux de CO 2 avec l'accroissement de la température du sol devrait être plus grand dans les sites à climat frais.cellulose / forêt japonaise / carbone organique du sol / respiration du sol

Revealing the size-dependency of traits (physiological and morphological properties) not only provides insights into species life history strategies but also contributes to the accurate prediction of changes in tree-and forest-level growth and responses to environments. We investigated the size-dependency of 18 leaf, wood, and bark traits related to resource use strategies and wood quality, using twenty 23-year-old Falcataria falcata trees with variable sizes (14.6 53.0 cm and 9.4 21.9 m in diameter at breast height [DBH] and height, respectively) in Okinawa, Japan. The radial variation in the wood density from the pith was also investigated. No leaf traits were correlated with DBH and height, whereas several wood and bark traits changed significantly with size. Larger trees produced dense wood with high water content and thick inner and outer bark, possibly reflecting the greater mechanical loads at the stem and greater translocation of carbon from the larger canopy. The radial gradients in wood density were steeper for small-sized trees, suggesting that age partially controlled xylem formation. We also found that fast growth did not compromise stem stiffness. Our results reveal the size-dependency differ between leaf and stem traits, possibly reflecting their different functional requirements. The size-related changes in traits observed here will be utilized for model parameterizations to predict changes in growth, carbon stocks, responses to environments, and wood quality in F. falcata plantations during the stand development.

Castanopsis sieboldii (Makino) Hatus. is one of the most popular evergreen broad-leaved species, distributing from Okinawa Pref. to the area beyond Kanto region, Japan. However, there are limited estimations of transpiration amounts with sap flow measurements, thereby very few knowledge of its characteristics of water use. Here we evaluated transpiration amounts of three trees of C. sieboldii based on the thermal dissipation method for 12 months from October 2020 to September 2021 within Forestry and Forest Products Research Institute, Ibaraki Pref., Japan. The minimum and maximum of transpiration amounts were found in mid-winter (January 2021) and early summer (June-July) , respectively. The crown conductance, which indicates the degree of stomatal openness for whole leaves of a tree, was saturated when daytime mean of solar radiation was more than 200 W m −2 . The crown conductance showed a decreasing trend with increasing daytime mean vapor pressure deficit. The daily mean value of soil water content to the depth of 40 cm was about 0.3 to 0.5 during the observation period, resulting in its less effect on the conductance. The optimum value of daytime mean air temperature for the conductance was found for the range of 10-20°C. The three trees showed isohydric behaviors, revealed by the analysis for the response of the conductance to vapor pressure deficit. Therefore, these test trees would avoid hydraulic failure with maintaining steady midday leaf water potential by closing stomata under extremely drought conditions.