Mitigation of nitrous oxide (N2O) emission from swine wastewater treatment in an aerobic bioreactor packed with carbon fibers

Mitigation of nitrous oxide (N₂O) emission from swine wastewater treatment was demonstrated in an aerobic bioreactor packed with carbon fibers (CF reactor). The CF reactor had a demonstrated advantage in mitigating N₂O emission and avoiding NOx (NO₃ + NO₂) accumulation. The N₂O emission factor was 0.0003 g N₂O‐N/gTN‐load in the CF bioreactor compared to 0.03 gN₂O‐N/gTN‐load in an activated sludge reactor (AS reactor). N₂O and CH₄ emissions from the CF reactor were 42 g‐CO₂ eq/m³/day, while those from the AS reactor were 725 g‐CO₂ eq/m³/day. The dissolved inorganic nitrogen (DIN) in the CF reactor removed an average of 156 mg/L of the NH₄‐N, and accumulated an average of 14 mg/L of the NO₃‐N. In contrast, the DIN in the AS reactor removed an average 144 mg/L of the NH₄‐N and accumulated an average 183 mg/L of the NO₃‐N. NO₂‐N was almost undetectable in both reactors.     

Influences of anthropogenic disturbances on the dynamics of white birch (Betula platyphylla) forests at the southern boundary of the Mongolian forest-steppe

We investigated the effects of disturbances on the dynamics of white birch-dominated forests at the southern boundary of the Mongolian forest-steppe. Dendroecological techniques were used to assess regeneration patterns and recent mortality trends in three stands with no evidence of recent anthropogenic disturbance (undisturbed) and four stands with evidence of cutting or fire (disturbed). In the undisturbed stands, only one distinct stem establishment was observed in the period between 1910 and 1950, and no establishment has been observed since then. In the disturbed stands, however, high establishment mainly by sprouting was observed in the period between 1960 and 1980. Percentages of standing dead stems were higher in the undisturbed stands than in the disturbed stands. Mean ages at death in the undisturbed stands were ≥70 years old. The high mortality was likely induced by the death of smaller stems due to light competition, whereas the mortality of larger stems was likely the result of tree senescence. In summary, the undisturbed stands seem to be in danger of decline due to a lack of regeneration during the last half of the previous century and recent high mortality rates of older stems, while the disturbed stands may be maintained for the next several decades by the younger cohort established between 1960 and 1980. White birch-dominated forests at the southern boundary of Mongolian forest-steppe have probably relied on relatively short disturbance intervals in the past because of the disturbance-dependent regeneration trait and relatively short longevity of Betula species.     

Long-term growth analyses of Japanese cedar trees in a plantation: neighborhood competition and persistence of initial growth deviations

The individual growth of tree diameter at breast height (dbh) is analyzed in an even-aged plantation of Cryptomeria japonica from stand age of 45 to 94 years, to examine how the growth of individual trees has been affected by the changes in spacing resulting from thinning operations. At any age, a significant proportion (0.37–0.46) of the variation in dbh growth during a 5–11-year period was explained by dbh at the beginning of the period, probably due to greater leaf mass of larger trees. Next, either one-sided or two-sided competition was added to the model, by calculating the basal area (BA) of neighboring trees around each tree within a given radius or BA for trees having larger dbh than the focal tree within the radius. After preliminary analyses, a radius of 8 m was selected as the critical range for tree competition. Although both types of competition explained a significant proportion (0.09–0.43) of growth variation, one-sided competition was not significant at ages greater than 54 years. Based on the model at 45 years of age, the initial deviation of growth rate for each tree from the predicted rate was calculated and added to the models as a third variable. This raised the coefficient of determination up to 0.50–0.74. These findings have practical significance for forest plantation management, particularly for controlling the growth of standing trees via thinning, to produce high-quality timber in the future.     

Nitrogen-fixing activity in decomposing litter of three tree species at a watershed in eastern Japan

Nitrogen fixation during litter decomposition was studied for 34 months using litterbags containing newly fallen litter of coniferous species Cryptomeria japonica and Pinus densiflora and that of deciduous species Quercus serrata. Litterbags were set in contact with the forest floor in a deciduous broad-leaved forest near the top of a slope and in a C. japonica stand at the middle of the slope at a watershed in eastern Japan. Nitrogen-fixing activity, estimated by acetylene reduction after 16 and 19 months of incubation, was 62.65–3.86 nmoles C₂H₄ h⁻¹ g⁻¹ DW in Cryptomeria litter, but only 1.07–0.09 in Pinus and 0.72–0.04 in Quercus. The rate of N increase in decomposing litter was highest in Cryptomeria. Fungal biomass in decomposing litter, estimated by ergosterol content, increased during the initial 16 months of incubation in Cryptomeria and Quercus, and during the initial 19 months of incubation in Pinus. The litter decomposition rate was highest in Cryptomeria among the three species, due to increased N content and fungal biomass in Cryptomeria litter. Thus, N increase in decomposing Cryptomeria litter affects the subsequent N dynamics and decomposition pattern.     

Structural unit of xylans from sugi (<Emphasis Type="Italic">Cryptomeria japonica</Emphasis>) and hinoki (<Emphasis Type="Italic">Chamaecyparis obtusa</Emphasis>)

Arabinoglucuronoxylans (AGXs) isolated from the holocellulose of sugi (Cryptomeria japonica) and hinoki (Chamaecyparis obtusa) contained one 4-O-methyl-d-glucopyranosyluronic acid (4-O-Me-d-GlcAp) residue per 6.2 d-xylopyranose (d-Xylp) residues and one 4-O-Me-d-GlcAp residue per 3.8 d-Xylp residues. These AGXs were subjected to partial acid hydrolysis. Analyses by size exclusion chromatography and electrospray-ionization mass spectroscopy of the neutral sugar fractions in the hydrolysates showed the presence of xylooligosaccharides having a degree of polymerization of 2-8 in addition to d-Xyl, suggesting that the AGXs from sugi and hinoki contained unsubstituted chains consisting of at least eight d-Xyl residues. The acidic sugars in the hydrolysates were separated into two series of aldouronic acids composed of 4-O-Me-d-GlcAp and d-Xylp by ion-exchange chromatography. The first series included aldouronic acids from aldobiouronic acid (4-O-Me-d-GlcAp-Xyl) to aldopentaouronic acids (4-O-Me-d-GlcAp-Xyl₄). The second series were aldouronic acids composed of two 4-O-Me-d-GlcAp residues and 2-4 d-Xyl residues. In these acidic sugars, the uronic acid side chains were located on two contiguous d-Xyl residues. These facts indicated that AGXs from sugi and hinoki had a structural unit containing two 4-O-Me-d-GlcAp residues on two contiguous d-Xyl residues as well as AGXs from spruce and larch.     

Differences of tensile strength distributions between mechanically high-grade and low-grade Japanese larch lumber III: effect of knot restriction on the strength of lumber

It is well known that the presence of knots in structural lumber is one of the most important strengthreducing factors. For practical purposes, visual grading including knot restriction is an effective method for nondestructive evaluation of strength. Edge knot restriction for not only visually graded lumbers but also mechanically graded lumbers is specified in the Japanese agricultural standards for glued laminated lumber. We conducted experimental studies on differences of tensile strength distributions between mechanically high-grade and low-grade Japanese larch (Larix kaempferi, carriere) lumbers daily used for manufacturing glued laminated timbers in Nagano, Japan. We then examined the additional visual grading of mechanically graded lumbers for nondestructive evaluation. We visually graded the prepared mechanically graded lumber by focusing on the knots' area ratio of grouped knots. We confirmed that the higher visual grade related to the stronger tensile strength, similar to our present knowledge; but the effects of knot restriction were reduced when the length of the lumber increased in view of nonparametric 5th percentiles of tensile strength. The differences in the strength/elasticity ratio between mechanically high-grade and low-grade lumber were negligible. It was clear that the length effect on the ratio in visually graded high-grade lumber was smaller than that of visually graded low-grade lumber. It was thus concluded that knot restriction should have little effect on the tensile strength of mechanically graded lumber.     

Changes in aboveground and belowground properties during secondary natural succession of a cool-temperate forest in Japan

Forest development in temperate regions is considered to be a global carbon sink. Many studies have examined forest development after harvesting or fire from aboveground (e.g., biomass) or belowground (e.g., soil nutrient) perspectives. However, few studies have explored forest development from both perspectives simultaneously in cool-temperate forests in Japan. In this study, we examined changes over 105 years in both aboveground and belowground components during secondary natural succession. The aboveground biomass increased for 50 years and reached a plateau in a 105-year-old stand. The N mineralization rate increased during succession for 50 years, but showed a decline in the 105-year-old stand due to the decrease in the nitrification rate in late succession. The percent nitrification (i.e., relative contribution of nitrification to N mineralization) decreased significantly with increasing forest stand age. The N mineralization rates had significant relationships with N concentrations of the dominant tree foliage and litter fall and with the amount of litter fall N. Meanwhile, other belowground properties (i.e., soil pH, phenol concentration, soil microbial respiration, and litter mass loss) did not show any significant relationship with forest stand age. This may be because the soil at the study sites was heterogeneous and consisted of Cambisols and Andosols, the latter of which originally has high organic matter content, and thus may have buffered the effect of the aboveground development. These results indicate that belowground N dynamics are more closely associated with aboveground development than other belowground properties in these forests.     

Chemical changes in steam-pressed kenaf core binderless particleboard

The effects of chemical changes in kenaf core binderless particleboards on the bonding performance and thickness swelling of boards were investigated by chemical and spectroscopic analyses. Mild steam-injection treatments (0.6–1.0MPa) caused significant degradation of hemicelluloses, lignin, and cellulose. Conventional hot pressing caused a lower degree of degradation of the chemical components. The hot-pressed kenaf core board without any binders showed poor bonding performance. Thus, it was found that partial degradation of the three major chemical components of the kenaf core by mild steam-injection treatment increased the bonding performance and dimensional stability of the binderless boards, and gave better quality binderless boards than those made by hot-pressing treatments.Part of this report was presented at the 4th International Wood Science Symposium, Serpong, Indonesia, September 2002; and at the 53rd Annual Meeting of The Japan Wood Research Society, Fukuoka, March 2003