Reactions between Cr(VI) and wood and its model compounds

Wood, macromolecular and simple model compounds, were reacted with CrO₃ or K₂CrO₄ aqueous solutions. Extracted lignin, guaiacol, vanillin, vanillyl alcohol and homovanillyl alcohol were chosen as model compounds for lignin, whilst cellulose, gum Ghatti, xylan, extracted hemicellulose from pine, methyl-β-D-glucopyranoside and methyl-β-cellobioside were used as models for wood polysaccharides. The kinetics of the reduction reactions of Cr(VI) were monitored using UV-Vis spectroscopy and the results obtained for several temperatures are discussed. In general terms, wood, lignin and lignin model compounds reduced Cr(VI) faster and to a greater extent than polysaccharides or simple sugar molecules. Moreover, lignin model compounds were reduced even faster than lignin. Simple sugars showed a reduction pattern similar to that of cellulose. Extracted hemicellulose revealed to be a poorer reductant while gum Ghatti was the strongest among the polysaccharides. As expected, CrO₃ aq. behaved as a more powerfull oxidant than K₂CrO₄ aq. for these substances. Even at 100 °C, sugars or polysaccharides did not seem to be oxidised by K₂CrO₄ aq. 0.01 M. These results suggest that, because of the differences in reactivity, lignin reacts preferentially when wood is treated with Cr(VI)-containing formulations, like those which are applied in wood preservation treatments.     

Evolution of CO2 during the fixation of chromium containing wood preservatives on wood

Summary A titration procedure was used to confirm carbon dioxide evolution from wood treated with solutions containing chromic acid and to quantify the effects of species (red pine vs soft maple), solution concentration and reaction temperature on the rate and amount of CO₂ evolved. Small blocks or chips were vacuum treated with either chromated copper arsenate (CCA) wood preservative or chromic acid solutions and the release of CO₂ monitored until the reaction was complete. Significant volumes of CO₂ were measured. This is attributed to the oxidation and subsequent decarboxylation of primary hydroxyl groups on wood constituents. The ratio of moles of CO₂ produced to moles of chromium added to the wood ranged from about 0.07 to 0.24 depending on the wood species, solution properties and fixation conditions. This accounted for from 9 to 32% of the total oxidation potential of the hexavalent chromium applied. The relative amounts of CO₂ produced were higher for maple than for red pine. The rate of CO₂ evolution was also higher in the maple samples, consistent with the higher rate of chromium reduction in soft maple compared to red pine. The amount of C0₂ produced was approximately proportional to the amount of hexavalent chromium in the CCA treating solution although the ratio of CO₂ produced to chromium added to the wood increased slightly with increasing solution concentration. The relative amounts of CO₂ produced increased with increasing fixation temperature over the 50–90 °C range in both species. The rate of CO₂ evolution was accelerated as the fixation temperature was increased. The rates and amounts of CO₂ produced were similar for CCA and Cr0₃ treatments containing the same concentration of chromic acid. Copper and arsenic components of the CCA solution did not appear to have any effect on the decarboxylation reaction.We gratefully acknowledge the financial support of the Natural Sciences and Engineering Research Council of Canada, Natural Resources Canada;, LPB Poles Inc., Masson Quebec, Timber Specialties Ltd., Campbellville Ontario and Guelph Utility Pole Co. Ltd., Guelph Ont. for this study.     

Reactions between Cr(VI) and wood and its model compounds

Hexavalent chromium solutions at two pH levels (about 1.3 and 7.8) were reacted with wood, gum ghatti, lignin, cellulose and simple model compounds representing wood chemical structures (guaiacol, vanillin, vanillyl alcohol, homovanillyl alcohol, methyl-(β-D-glucoside, and methyl-β-cellobioside). Reaction products were isolated and characterised by elemental analysis, magnetic susceptibility, and Fourier-transform infrared spectroscopy (FTIR). Data suggest that all the chromium present in the reaction products is in its trivalent oxidation state. After reduction reactions, wood and macromolecular substances generally fixed a relatively low level of chromium, which contrasts with the high level in the products isolated from the reaction with the model compounds. It appears that the reaction of the simple model compounds with Cr(VI) did not produce complex adducts of Cr(III) but inorganic substances, of the hydrated chromium oxide type. Therefore, under the experimental conditions applied, simple model compounds do not seem to behave chemically as wood or as the macromolecular substances investigated. Hence, their significance as model compounds must be object of further assessment. An exception is the product from the reaction of vanillyl alcohol and K₂CrO₄ aq. This contains a relatively small amount of chromium and its FTIR spectrum presents rather well defined bands indicating reaction of the phenolic hydroxyl and secondary alcohol groups. This system must be worthy of further investigation as a model for lignin.     

Replication of wood into biomorphous nanocrystalline Y<Subscript>2</Subscript>O<Subscript>3</Subscript>:Eu<Superscript>3+</Superscript> phosphor materials

Biomorphous Eu³⁺-doped Y₂O₃ was fabricated by replication of wood templates using vacuum-assisted infiltration of a water-based sol–gel mixture and subsequent calcination at 750°C. The precursor sols were prepared from (Y_0.95Eu_0.05)₂O₃ dissolved in 10 vol% nitric acid and adding citric acid as the chelating agent. X-ray powder diffraction analyses and Rietveld refinements confirmed that the calcined samples were solely composed of bixbyite Y₂O₃:Eu³⁺ phase with a mean crystallite size of 16 nm. Scanning electron micrographs and cathodoluminescence imaging showed that the cellular preform anatomy was retained and that the original wood cell walls were completely transformed into phosphor struts with pore sizes ranging from 5 to 20 μm. The optical properties of the biomorphous phosphor materials were analyzed by photoluminescence spectroscopy and assigned to the characteristic Eu³⁺ (4f⁶ → 4f⁶) electric dipole or magnetic dipole transitions. From fluorescence lifetime measurements, the mean lifetime was calculated as 1.62 ms.     

Impacts of initial stand density and thinning regimes on energy wood production and management-related CO<Subscript>2</Subscript> emissions in boreal ecosystems

An ecosystem model (Sima) was utilised to investigate the impact of forest management (by changing both the initial stand density and basal area thinning thresholds from current recommendations) on energy wood production (at energy wood thinning and final felling) and management-related carbon dioxide (CO₂) emissions for the energy wood production in Finnish boreal conditions (62°39′ N, 29°37′ E). The simultaneous effects of energy wood, timber and C stocks in the forest ecosystem (live and dead biomass) were also assessed. The analyses were carried out at stand level during a rotation period of 80 years for Scots pine (Pinus sylvestris L.) and Norway spruce (Picea abies L. Karst.) growing in different fertility sites. Generally, the results showed that decreased basal area thinning thresholds, compared with current thinning, reduced energy wood (logging residues) and timber production, as well as carbon stocks in the forest ecosystem. Conversely, increased thinning thresholds increased energy wood production (ca. 1–27%) at both energy wood thinning and final felling and reduced CO₂ emissions (ca. 2–6%) related to the production chain (e.g. management operations), depending on the thinning threshold levels, initial stand density, species and site. Increased thinning thresholds also enhanced timber production and carbon stocks in the forest ecosystem. Additionally, increased initial stand density enhanced energy wood production for energy wood thinning for both species, but this reduced energy wood production at final felling for Scots pine and Norway spruce. This study concluded that increases in both initial stand density and thinning thresholds, compared with the current level, could be useful in energy wood, timber and carbon stocks enhancement, as well as reducing management-related CO₂ emissions for energy wood production. Only 2.4–3.3% of input of the produced energy (energy wood) was required during the whole production chain, depending on the management regime, species and sites. However, a comprehensive substitution analysis of wood-based energy, in respect to environmental benefits, would also require the inclusion of CO₂ emissions related to ecosystem processes (e.g. decomposition).     

Nutrient contents and efficiencies of beech and spruce saplings as influenced by competition and O<Subscript>3</Subscript>/CO<Subscript>2</Subscript> regime

Saplings of Fagus sylvatica and Picea abies were grown under conditions of intra and interspecific competition in a 2-year phytotron study under combinations of ambient and elevated ozone (+O₃ which is 2 × O₃, but <150 nl l⁻¹) as well as carbon dioxide concentrations (+CO₂ which is amb. CO₂ + 300 μl CO₂ l⁻¹) in a full factorial design. Saplings were analysed for various mineral nutrients in different plant organs as well as biomass production and crown development. The study was based on the assumption that nutritional parameters important for growth and competitiveness are affected by stress defence under limiting nutrient supply. The hypotheses tested were (1) that nutrient uptake-related parameters (a) as well as efficiencies in nutrient use for above-ground competition (b) of beech rather than spruce are impaired by the exposure to elevated O₃ concentrations, (2) that the efficiency in nutrient uptake of spruce is enhanced by elevated CO₂ concentrations in mixed culture, and (3) that the ability to occupy above-ground space at low nutrient cost is co-determinant for the competitive success in mixed culture. Clear nitrogen deficiencies were indicated for both species during the 2-year phytotron study, although foliar nitrogen-biomass relationships were not so close for spruce than for beech. O₃ stress did not impair nutrient uptake-related parameters of beech; thus hypothesis (1a). was not supported. A negative effect of elevated O₃ (under amb. CO₂) on the N and P based efficiencies in above-ground space occupation (i.e. lower crown volume per unit of N or P invested in stems, limbs and foliage) of beech supported hypothesis (1b). It appeared that ozone stress triggered a nutrient demand for stress defence and tolerance at the expense of above-ground competition (trade-off). Crown volume of beech under O₃ stress was stabilized in monoculture by increased nutrient uptake. In general, the +CO₂-treatment was able to counteract the impacts of 2 × O₃. Elevated CO₂ caused lower N and S concentrations in current-year foliage of both tree species, slightly higher macronutrient amounts in the root biomass of spruce, but did not increase the efficiencies in nutrient uptake of spruce in mixed culture. Therefore hypothesis (2) was not supported. At the end of the experiment spruce turned out to be the stronger competitor in mixed culture as displayed by its higher total shoot biomass and crown volume. The amounts of macronutrients in the above-ground biomass of spruce individuals in mixed culture distinctly exceeded those of beech, which had been strongly reduced by interspecific competition. The superior competitiveness of spruce was related to higher N and P-based efficiencies in above-ground space occupation as suggested in hypothesis (3). This article belongs to the special issue “Growth and defence of Norway spruce and European beech in pure and mixed stands”.     

New piezoelectric moduli of wood: <Emphasis Type="Italic">d</Emphasis><Subscript>31</Subscript> and <Emphasis Type="Italic">d</Emphasis><Subscript>32</Subscript>

This article reports the piezoelectric moduli of wood d ₃₁, d ₃₂, and d ₃₆. The piezoelectric moduli of wood d ₃₁ and d ₃₂ have not been previously reported, although there has been much research on the d ₁₄ and d ₂₅ moduli of wood. The moduli d ₃₁, d ₃₂, and d ₃₆ were measured carefully because their absolute values were considerably smaller than those of d ₁₄ and d ₂₅. For Softwoods, d ₃₆ values were mostly negative, whereas the values for hardwoods had either positive or negative values. The other moduli, d ₃₁ and d ₃₂, were a mixture of positive and negative values in softwoods and hardwoods. The existence of d ₃₁ and d ₃₂ suggests the presence of an electrical polarity of the cellulose crystal in the fiber direction of the wood. The polarities of d ₃₁ and d ₃₂ became clear from wood in the outer part of the trunk, where the crystallinity of cellulose is large and the alignment of the crystals becomes parallel to the fiber direction.     

Relationship between degradation of wood and production of H2O2-producing or one-electron oxidases by brown-rot fungi

Summary The one-electron oxidation activity of brown-rot fungi was determined by measuring ethylene production from KTBA. Ethylene production was related to degradation of lignin, cellulose, and wood itself. Extracellular protein that catalyzed oxidation of KTBA was isolated from wood-containing cultures. This protein required H₂O₂ for KTBA oxidation. It was also found to oxidize NADH, producing H₂O₂ via in the presence of O₂. The protein showed little phenol-oxidase activity under conditions giving high activity against KTBA. The results indicate that partially reduced oxygen may play a role in the initial degradation of the cellulose and lignin in wood in cultures of brown-rot fungi.     

Micropore structure of wood: Change in micropore structure accompanied by delignification

In our preceding study, we clarified that liquids having similar molecular sizes to ethanol were mainly adsorbed onto lignin among the major constituents of wood. This suggests that most micropores or adsorption sites loosely hydrogen-bonded to each other, which are accessible to these liquids, exist in lignin. In the present study, to examine micropores in wood and lignin, micropore distribution was measured by CO₂ gas adsorption at ice-water temperature (273 K). Dry samples prepared by gradual delignification from wood meal were used as adsorbents. The pore-size distributions were determined by analyzing adsorption isotherms using the Horvath-Kawazoe method. It was found that the number of micropores decreased with the decrease in residual lignin, and micropores were hardly found in cellulose and hemicellulose. It is considered that most micropores smaller than 0.6 nm in wood exist in lignin.     

Difference in cutting age for highest profit by methods for calculating CO<Subscript>2</Subscript> emission trading and the price of CO<Subscript>2</Subscript>

 The amounts of CO₂ that are absorbed and emitted by forest in a model stand area were determined using two calculation methods, namely the flow approach and the stock approach for emission trading, to understand the relationships between the cutting age for the highest profit rate (CAHPR; optimum tree ages to be cut so as to maximize the profit) and (1) the prices of CO₂ and (2) the balance between CO₂ emission and absorption. The resultant CAHPR differed between these two CO₂ accounting methods, which give different tree ages for maximum log volume yield. A rise in CO₂ price caused the CAHPR to approach the tree age of maximum log volume in the flow approach method, and to deviate from the tree age of maximum log volume in the stock approach method. Even at the same CO₂ price, the CAHPR differed between the CO₂ accounting methods. At low CO₂ prices, the CAHPR did not affect situations where the difference of average profit is large by cutting age. On the other hand, the CAHPR was greatly affected at low CO₂ prices when the mean log volume growth changed with tree age. These trends were found to be universal. Received: September 18, 2001 / Accepted: October 25, 2002 Acknowledgments This study is one of the fifth science study subsidy projects of the Japan Forest Technology Association. Correspondence to:K. Sakata     

Soil CO<Subscript>2</Subscript>, CH<Subscript>4</Subscript> and N<Subscript>2</Subscript>O emissions from production fields with planted and remnant hedgerows in the Fraser River Delta of British Columbia

Planting hedgerows on farm field edges can help mitigate greenhouse gas (GHG) emissions from agricultural landscapes by sequestering carbon (C) in woody biomass and in soil. Sequestration rates however, must be assessed in terms of their overall global warming potential (GWP) which must also consider GHG emissions. The objectives of this study were to (1) compare carbon dioxide (CO₂), methane (CH₄) and nitrous oxide (N₂O) emissions from two types of hedgerows and adjacent annual agricultural production fields, and 2) better understand how climate, soil properties and plant species configurations affect hedgerow GHG emissions. At eight study sites in the lower Fraser River delta of British Columbia, we measured emissions from soil in both planted (P-Hedgerow) and remnant hedgerows (R-Hedgerow), as well as in adjacent annual crop production fields over 1 year using a closed-static chamber method. CO₂ emissions were 59 % higher in P-Hedgerow than R-Hedgerow, yet there were no significant differences of relative emissions of CH₄ and N₂O. The environmental variables that explained the variation in emissions differed for the three GHGs. CO₂ emissions were significantly correlated with soil temperature. CH₄ and N₂O and emissions were marginally significantly correlated with soil organic carbon (SOC) and soil water-filled pore space (WFPS), respectively. Emissions were not significantly correlated with hedgerow plant species diversity. While hedgerows sequester carbon in their woody biomass, we demonstrated that it is critical to measure hedgerow emissions to accurately ascertain their overall GHG mitigation potential. Our results show that there are no CO₂e emission differences between the management options that plant new diverse hedgerows or conserve existing hedgerows.     

Reaction wood anatomy and lignin distribution in <Emphasis Type="Italic">Gnetum gnemon</Emphasis> branches

This study investigated the anatomical and chemical characteristics of the reaction wood of a gymnpsperm species, Gnetum gnemon, and discussed on contributing factor for the type of reaction wood in this species. Cell morphology, microfibril angle (MFA) of the S₂ layer and lignin distribution in secondary walls of tracheary elements, and lignin content were examined on three branches. Observations included no G-layer formation, significant decreases in vessel frequency, and altered MFA, and visible-light absorbance after lignin colour reactions in tracheid and fiber tracheid walls on the upper side in almost all samples. These results suggest that reaction wood in G. gnemon was similar to that in ‘tension-wood-like-reaction wood’ in angiosperms. On the other hand, reaction wood showed decrease in the lignin concentration in the fiber tracheid walls compared to the tracheid walls. In addition, the lignin in the tracheid and fiber tracheid walls was originally rich in syringyl units, suggesting that changes in the anatomical and chemical characteristics of secondary xylem due to reaction wood formation might relate to the ratio of the syringyl to guaiacyl units in lignin in the cell walls which function for mechanical support.     

Crop residue effect on crop performance,soil N<Subscript>2</Subscript>O and CO<Subscript>2</Subscript> emissions in alley cropping systems in subtropical China

Land management practices that simultaneously improve soil properties are crucial to high crop production and minimize detrimental impact on the environment. We examined the effects of crop residues on crop performance, the fluxes of soil N₂O and CO₂ under wheat-maize (WM) and/or faba bean-maize (FM) rotations in Amorpha fruticosa (A) and Vetiveria zizanioides (V) intercropping systems on a loamy clay soil, in subtropical China. Crop performance, soil N₂O and CO₂ as well as some potential factors such as soil water content, soil carbon, soil nitrogen, microbial biomass and N mineralization were recorded during 2006 maize crop cultivation. Soil N₂O and CO₂ fluxes are determined using a closed-based chamber. Maize yield was greater after faba bean than after wheat may be due to differences in supply of N from residues. The presence of hedgerow significantly improved maize grain yields. N₂O emissions from soils with maize were considerably greater after faba bean (345 g N₂O–N ha⁻¹) than after wheat (289 g N₂O–N ha⁻¹). However, the cumulated N₂O emissions did not differ significantly between WM and FM. The difference in N₂O emissions between WM and FM was mostly due to the amounts of crop residues. Hedgerow alley cropping tended to emit more N₂O than WM and FM, in particular A. fruticosa intercropping systems. Over the entire 118 days of measurement, the N₂O fluxes represented 534 g N₂O–N ha⁻¹ (AWM) and 512 g N₂O–N ha⁻¹ (AFM) under A. fruticosa species, 403 g N₂O–N ha⁻¹ (VWM) and 423 g N₂O–N ha⁻¹ (VFM) under Vetiver grass. We observed significantly higher CO₂ emission in AFM (5,335 kg CO₂–C ha⁻¹) from June to October, whereas no significant difference was observed among WM (3,480 kg CO₂–C ha⁻¹), FM (3,302 kg CO₂–C ha⁻¹), AWM (3,877 kg CO₂–C ha⁻¹), VWM (3,124 kg CO₂–C ha⁻¹) and VFM (3,309 kg CO₂–C ha⁻¹), indicating the importance of A. fruticosa along with faba bean residue on CO₂ fluxes. As a result, crop residues and land conversion from agricultural to agroforestry can, in turn, influence microbial biomass, N mineralization, soil C and N content, which can further alter the magnitude of crop growth, soil N₂O and CO₂ emissions in the present environmental conditions.     

Branch CO<Subscript>2</Subscript> efflux in vertical profile of Norway spruce tree

Branch CO₂ efflux of Norway spruce tree [Picea abies (L.) Karst.] was measured in ten branches at five different whorls during the growing season 2004 (from June till October) in campaigns of 3–4 times per month at the Beskydy Mts., the Czech Republic. Branch CO₂ efflux was measured using a portable infrared gas analyzer (LI-6250, LI-COR, Inc., USA), operating as a closed system. Branch woody-tissue temperature was measured continuously in 10-min intervals for each sample position during the whole experiment period. On the basis of relation between CO₂ efflux rate and woody-tissue temperature, a value of Q₁₀ and of normalized CO₂ efflux rate (E₁₀–CO₂ efflux rate at 10°C) was calculated for each sampled position. Estimated Q₁₀ values ranged from 2.12 to 2.89, and E₁₀ ranged from 0.41 to 1.19 μmolCO₂m⁻²s⁻¹. Differences in branch CO₂ efflux were found between orientations, east-side branches presented higher efflux rate than west-side branches. The highest branch CO₂ efflux rate values were measured in August and the lowest in October, which corresponds with woody-tissue temperature and growth processes during these periods. Branch CO₂ efflux was significantly and positively correlated with branch position within canopy and woody-tissue temperature. Branches from the upper whorls showed higher CO₂ efflux activity and seasonal dynamics than branches from the lower whorls.     

Effects of elevated atmospheric CO<Subscript>2</Subscript> on two southern forest diseases

Research into the effects of rising atmospheric carbon dioxide (CO₂) on plant diseases remains limited despite the economic importance of this subject. Loblolly pine (Pinus taeda) seedlings were exposed to ambient and twice ambient levels of atmospheric CO₂ prior to inoculation with the fusiform rust fungus (the obligate pathogen Cronartium quercuum f.sp. fusiforme, CQF) or the pitch canker fungus (the facultative pathogen Fusarium circinatum, FC). Additionally, northern red oak seedlings (Quercus rubra; an alternate host of CQF) were exposed to ambient or elevated levels of atmospheric CO₂ prior to inoculation with CQF. In all cases, disease incidence (percent of plants infected) and disease severity (proportion of each plant affected) were determined; with the oak seedlings, the latent period (time to sporulation) was also monitored. In general, disease incidence was decreased by exposure to elevated CO₂. This exposure also increased the latent period for CQF on oak seedlings. In no instance did exposure to elevated CO₂ affect disease severity. This research demonstrated that plants may benefit from exposure to the increasing concentration of CO₂ in the atmosphere through decreases in fungal disease incidence.     

Evaluation of NO<Subscript>2</Subscript> sorption of cedar wood (<Emphasis Type="Italic">Cryptomeria Japonica</Emphasis>) with difference of the specimen size and contact condition between NO<Subscript>2</Subscript> gas and specimen using new test system

We developed a new system for measuring the NO₂ sorption ability of Japanese cedar (Cryptomeria japonica) wood by referring to Japanese Industrial Standard for JIS R 1701-1 (Test method for air purification performance of photocatalytic materials, Japanese Standard Association, Tokyo, 2004). Aeration experiments were conducted using plated specimen, particle specimen, discoid specimen and wood powder with consideration of aeration condition and surface area which can contact with NO₂ gas. In the plated specimen, the NO₂ sorption ability was greatly affected by the thickness of longitudinal direction, and high NO₂ sorption ability of the transverse section was observed within a thickness range from the surface to ca. 3 mm. The average NO₂ sorption volume for discoid specimen for 5 h was approx. five times larger than that those for the plated and particle specimens, which the thickness of longitudinal direction was 1.5 mm. This means that the NO₂ sorption effect was especially high under the condition where the NO₂ gas passed through tracheid. Also, it was suggested that the interface area between NO₂ gas and specimen influenced to the NO₂ sorption ability. Furthermore, it was confirmed that the NO₂ sorption volume in discoid specimen and the grain size below 0.25–0.50 mm of wood powder reached the greatest.     

Effects of long-term elevated CO<Subscript>2</Subscript> on N<Subscript>2</Subscript>-fixing,denitrifying and nitrifying enzyme activities in forest soils under <Emphasis Type="Italic">Pinus sylvestriformis</Emphasis> in Changbai Mountain

A study was conducted to determine the effects of elevated CO₂ on soil N process at Changbai Mountain in Jilin Province, northeastern China (42°24′N, 128°06′E, and 738 m elevation). A randomized complete block design of ambient and elevated CO₂ was established in an open-top chamber facility in the spring of 1999. Changpai Scotch pine (Pinus sylvestris var. sylvestriformis seeds were sowed in May, 1999 and CO₂ fumigation treatments began after seeds germination. In each year, the exposure started at the end of April and stopped at the end of October. Soil samples were collected in June and August 2006 and in June 2007, and soil nitrifying, denitrifying and N₂-fixing enzyme activities were measured. Results show that soil nitrifying enzyme activities (NEA) in the 5–10 cm soil layer were significantly increased at elevated CO₂ by 30.3% in June 2006, by 30.9% in August 2006 and by 11.3% in June 2007. Soil denitrifying enzyme activities (DEA) were significantly decreased by elevated CO₂ treatment in June 2006 (P < 0.012) and August 2006 (P < 0.005) samplings in our study; no significant difference was detected in June 2007, and no significant changes in N₂-fixing enzyme activity were found. This study suggests that elevated CO₂ can alter soil nitrifying enzyme and denitrifying enzyme activities. Foundation project: This research was supported by the National Natural Science Foundation of China (No. 90411020) and Major State Basic Research Development Program of China (973 Program) (2002CB412502).     

Structural characteristics of cell walls of kenaf (<Emphasis Type="Italic">Hibiscus cannabinus </Emphasis>L.) and fixation of carbon dioxide

 Kenaf (Hibiscus cannabinus) plants are widely known for their contribution to the global and regional environment because of their ability to fix CO₂. On the other hand, some scientists have doubts about CO₂ fixation by kenaf and have misgivings about the effect of kenaf on the ecosystem. We have characterized the structural characteristics of cell walls of bast fibers, cores, roots, and leaves of kenaf during the maturation of plants and investigated the rate of photosynthesis. During maturation of the kenaf plant the cellulose (bast fiber 52–59%, core 44–46%) and lignin (bast fiber 9.3–13.2%, core 18.3–23.2%) contents increased significantly. The aromatic composition of the lignin of bast fiber was significantly different from that of the core lignin and of other plants. The lignin of bast fiber appears similar to pure syringyl lignin. Fixation of CO₂ by kenaf plants and their contribution to the global environment are discussed. A significatly high rate of photosynthesis of kenaf plants was observed compared to that of woody plants in Japan, but the amount of CO₂ fixation depends on the characteristics of the plantation. If the kenaf was planted in high density, about twice as much CO₂ was fixed as was fixed by trees in a tropical rain forest. Received: April 22, 2002 / Accepted: July 24, 2002 Acknowledgments This project was supported by the Science and Technology Agency (STA) fellowship of the Japan International Science and Technology Exchange Center (JISTEC), which has been successfully applied by Dr. Shuji Hosoya, Forestry and Forest Products Research Institute. We thank Dr. Toshio Sumizono and Mr. Masao Sakurai, Forestry and Forest Products Research Institute, for their kind help in determining the rate of photosynthesis and cultivating the kenaf plants, respectively. We also express our appreciation to Dr. Quang Hung Le, College of Agriculture and Forestry, Ho Chi Minh City, Vietnam for offering information about the cultivation of kenaf at Thu Duc District, Ho Chi Minh City.     

Soil CO<Subscript>2</Subscript> emissions in agricultural watersheds with agroforestry and grass contour buffer strips

The potential for agricultural soils to act as a sink and sequester carbon (C) or a source and emit carbon dioxide (CO₂) is largely dependent upon the agricultural management system. The establishment of permanent vegetation, such as trees and grass contour buffer strips, may cause accumulation of above- and below-ground C over time, thereby acting as a sink for tropospheric CO₂. However, the effects of contour grass strips and grass-tree strips (agroforestry) on soil CO₂ emissions have not been extensively studied in row-crop watersheds in the temperate regions. The objective of this study was to determine the effects of agroforestry and grass contour buffer strips and landscape position on soil surface efflux rate of CO₂ in three adjacent agricultural watersheds with claypan soils in northeast Missouri. The three watersheds were in a corn-soybean rotation, and contained (1) cropped only (CR), (2) cropped with grass contour strips (GR), or (3) cropped with tree-grass contour strips (AF) management systems. Soil surface CO₂ efflux was measured throughout the 2004 growing season at the upper (UBS), middle (MBS), and lower (LBS) backslope landscape positions within the three watersheds. The cumulative soil CO₂ production was lowest in the CR (0.9 kg CO₂-C m⁻²) compared to the AF (1.5 kg CO₂-C m⁻²) and GR watersheds (1.5 kg CO₂-C m⁻²). The lower backslope position (1.6 kg CO₂-C m⁻²) across all three watersheds produced 32 and 40% greater cumulative soil CO₂ than the upper and middle backslope positions, respectively. A 72-day incubation study determined the effects of 40, 60, 80, and 100% soil water-filled pore space (WFPS) and N rate (0 and 1.39 g KNO₃ kg soil⁻¹) on soil CO₂ efflux from bulk soil collected under each management system. The cumulative CO₂ production was highest in the grass soil (1,279 mg CO₂-C kg soil⁻¹) compared to the agroforestry (661 mg CO₂-C kg soil⁻¹) and cropped (483 mg CO₂-C kg soil⁻¹) soils regardless of WFPS and N rate. The highest cumulative CO₂ production for the grass soil (1,279 mg CO₂-C kg soil⁻¹) occurred at 80% WFPS, and was approximately 2 to 2.6 times greater than the agroforestry and cropped soils at 80% WFPS. The results of this study indicate that conservation management practices, such as grass and grass-tree contour buffer strips, and landscape position affect soil surface CO₂ production and accumulation of soil organic C that may influence soil C sequestration.     

Curing and degradation processes of cement-bonded particleboard by supercritical CO<Subscript>2</Subscript> treatment

This study examined the effects of supercritical CO₂ treatment on the curing and degradation of cementbonded particleboard (CBP). Significant correlations were found between the supercritical CO₂ treatment and mechanical properties during both curing and degradation processes. Internal bond (IB) strength, modulus of rupture (MOR), and modulus of elasticity (MOE) values of CBP achieved their maximums by supercritical CO₂ treatment in 30 min. These conditions indicated that supercritical CO₂ treatment accelerates the curing process rapidly and enhances the mechanical properties of the CBP. However, these values decreased in treatment from 60 min to 10 days and had a negative effect on board performance, indicating that supercritical CO₂ treatment over a longer time span leads to degradation of the CBP. Furthermore, X-ray diffractometry (XRD), thermal gravimetry (TG-DTG), and scanning electron microscopy (SEM) observation clarified that the mechanisms of degradation are directly affected by the mineralogical composition of the system, in par ticular, by the calcium carbonate content as caused by carbonation.