木聚糖酶水解制取低聚木糖的研究

比较了木聚糖酶和纤维素酶水解木聚糖制备低聚木糖的效果，并在10L酶解罐中研究了搅拌速率和酶解时间等因素对木聚糖酶水解的影响。优化了酶解工艺条件，当木聚糖质量浓度为30g/L，木聚糖酶体积用量为1%，搅拌速率180r/min时，酶解2h低聚糖得率可达35.2%。总糖得率为41.9%。产品酶解液中25.9%固形物是聚合度2-5的低聚木糖。     

低聚木糖生产废渣纤维素酶诱导和水解特性的研究

研究了生产低聚木糖(XOS)所得的废渣对里氏木霉纤维素酶合成的诱导作用和纤维素酶水解特性.废渣对里氏木霉合成纤维素酶的诱导作用较差,而纤维素酶水解性能优异.里氏木霉以含纤维素15 g/L的废渣为碳源合成纤维素酶,滤纸酶活为0.48 FPIU/mL,酶产率为6.67 FPIU/(L·h),酶得率为每克纤维素32.00 FPIU,而在相同条件下以玉米芯为碳源时滤纸酶活为3.20 FPIU/mL、酶产率19.00 FPIU/(L·h)和酶得率每克纤维素213.33 FPIU.质量浓度为20 g/L的废渣在酶用量为每克纤维素10 FPIU条件下水解24 h,水解得率达92.8 %;底物废渣质量浓度为100 g/L时,48 h纤维素酶水解得率达到80.6 %.     

蒸汽爆破预处理对红柳木质组分及酶解性能的影响

以红柳为材料研究蒸汽爆破预处理强度系数lgR对木质组分和纤维素酶水解性能的影响。结果表明:蒸汽爆破处理对红柳中纤维素和木质素含量的影响并不显著,但是它可以有效破坏红柳的天然物理结构,并且导致大部分半纤维素(木聚糖)产生自水解反应生成单糖和低聚糖溶出,同时产生乙酸、甲酸和糠醛等小分子降解产物。基于纤维素回收率和纤维素酶水解得率分析,在蒸汽爆破强度系数达到4.239时(爆破温度210℃和保温时间10min)对红柳的预处理效果最佳,汽爆物料中纤维素的含量可达到52.4%,残余木聚糖含量仅为2.01%,并生成0.76%甲酸和3.17%乙酸。采用每克纤维素20.0FPIU的纤维素酶用量水解5%(w/w)该汽爆红柳物料48h,纤维素酶水解得率可达到86.6%(未处理的原料仅为15.5%)。这表明无化学品添加的蒸汽爆破是适于红柳糖化及生物炼制的一种有效的预处理方法。     

葡甘露低聚糖的酶法制备及其对肠道微生物的增殖作用

为提高酶法制备葡甘露低聚糖得率,并阐明其对肠道微生物增殖的作用,研究了不同碳源诱导物对甘露聚糖酶酶系组成以及葡甘露聚糖酶解过程中工艺参数对葡甘露低聚糖得率的影响,研究了葡甘露低聚糖对典型肠道微生物的增殖作用及其代谢产物。结果表明,微晶纤维素是里氏木霉合成甘露聚糖酶的最佳碳源诱导物,里氏木霉以10 g/L微晶纤维素为诱导物产酶,β-甘露聚糖酶活力为3.902 U/mL,β-甘露糖苷酶活力为0.019 U/mL,两者酶活比为205.4∶1.0。15 g/L葡甘露聚糖在甘露聚糖酶用量10 U/g、50℃、pH 4.8条件下水解8 h,葡甘露低聚糖得率可达73.70%,酶对葡甘露低聚糖的选择性为85.60%。以3 g/L葡甘露低聚糖为碳源的肠道微生物进行体外培养,结果显示长双歧杆菌等14种有益菌能有效利用葡甘露低聚糖进行增殖和代谢,产生短链脂肪酸,而平肠球菌等3种潜在致病菌几乎不能利用葡甘露低聚糖;长双歧杆菌(Bifidobaterium longum ATCC15697)和嗜酸乳杆菌(Lactobacillus acidophilus B-4495)的增殖效果最好,分别增殖了27.0和19.5倍,生成的短链脂肪酸(乙酸、丙酸、丁酸和乳酸)浓度分别为(78.5±3.5)和(42.6±2.6) mmol/L。     

选择性控制酶水解玉米芯木聚糖制备低聚木糖

对采用选择性控制木聚糖酶水解条件制备低聚木糖进行了研究,并同时探讨了以两种木聚糖形式--干粉和湿浆为原料造成的酶解结果差异及其原因.结果表明,目前较适宜的低聚木糖制备工艺为以木聚糖湿浆为底物,底物质量浓度20～40g/L,酶用量1%(体积分数,下同),pH值4.8,温度50℃,酶解时间4 h.造成干粉与湿浆酶解制备低聚糖结果差异的原因,可能是由于这两种底物自身结构特性的差异导致了底物可及度,以及酶与底物吸附作用的不同.结果显示当以干粉为底物,酶用量10%,酶解时间12 h,低聚木糖得率最高可达40%(质量分数)左右,而以湿浆为底物,达到同样低聚糖得率的酶用量和酶解时间分别仅需1%和4 h.     

杨木加工剩余物化学水解制备糠醛的研究

以杨木单板旋切木芯和原木制材锯屑为原料,以液体质子酸为催化剂,采用常压低温酸催化水解法制备糠醛.考察了不同催化剂和助催化剂种类及用量等因素对糠醛得率的影响.实验结果表明,较适宜的水解工艺条件是:加料为200 g时、水解反应温度为140～160℃、反应时间为6 h、浓度为8%的硫酸用量为600 ml、氯化钠为140 g、氯化铁10 g,两种原料的糠醛得率分别为4.51%和5.24%.     

亚硫酸盐蔗渣浆的纤维素酶水解及其机理研究

研究了影响纤维素酶水解亚硫酸盐蔗渣浆的一些影响因素,采用离子色谱、X射线衍射(XRD)、傅里叶红外光谱(FT-IR)和原子力显微镜(AFM)对水解液成分、纤维素超分子结构及纤维形态的变化进行了分析。结果表明,在最适条件下,未漂浆和漂白浆的水解得率分别为74.89%和70.67%,漂白浆的水解得率低于未漂浆。水解产生的纤维二糖的质量浓度随反应进行逐渐降低,其中未漂浆的纤维二糖质量浓度由6 h时的7.95 g/L降到了72 h时的2.44 g/L,漂白浆的纤维二糖质量浓度由6 h时的6.59 g/L降到了72 h时的3.11 g/L。酶解使纤维素结晶度升高,但没有改变晶型。     

酸催化的蒸汽爆破预处理强度对麦草酶水解影响的研究

以蒸汽爆破法对0.5 %的稀硫酸浸渍的麦草进行预处理,研究了不同处理强度对麦草浆得率、半纤维素回收率、纤维素回收率、纤维素酶水解得率产生的影响.实验结果表明,在蒸汽爆破预处理过程中,麦草纤维组分发生分离.随着处理强度的提高,粗浆得率降低,细浆得率上升,纤维素的降解程度和半纤维素的去除程度提高,酶水解得率相应提高.在处理强度为4.14的预处理条件下,半纤维素的水解程度最大,而细浆得率和纤维素的酶解得率最高,分别为62.0 %和73.4 %;最佳的处理强度为3.55,此条件下,汽爆麦草原料细浆中的葡萄糖得率和滤出液中总糖的得率最高,分别为20.0 %和13.0%.     

高温高压制备微晶纤维素新工艺

高温高压制备微晶纤维素工艺与传统的制备工艺的反应机理相近,随着处理液pH值、时间、温度、压力等反应相关因素的调整,其反应进程发生重大变化,并且产生与传统工艺截然不同的结果。实验结果表明,制备过程因素影响关系为:酸浓度<处理时间<水解温度;从得率对比情况看,高温高压制备微晶纤维素的工艺水解反应时间过长,则纤维素反应物明显减少,其得率明显偏低,合理控制处理时间是保证有效得率的重要环节。从不同工艺条件下微晶纤维素得率角度,高温高压制备微晶纤维素的最佳工艺为:盐酸浓度取2.5%、处理时间为180 min、水解温度为130℃;但以表面膨胀体积为参照系时,高温高压制备微晶纤维素的最佳工艺为:此时盐酸浓度应取1.0%、处理时间为120 min、水解温度为150℃。     

酶法糖化玉米芯发酵生产乙醇的研究

研究了玉米芯的酶法水解及酶解液的乙醇发酵。采用里氏木霉ZU-02纤维素酶水解酸预处理后的玉米芯为原料,适宜的酶用量为20 FPIU(以每克底物计,下同),48 h后酶解得率为67.5%;添加黑曲霉ZU-07所产纤维二糖酶可有效解除纤维二糖累积引起的反馈抑制作用,当纤维二糖酶用量为6.5 CB IU时,48 h后酶解得率提高到83.9%。采用分批补料酶解工艺,使底物质量浓度提高到200 g/L,酶解60 h后还原糖质量浓度达到116.3 g/L,酶解得率为80.1%。利用一株耐高温酿酒酵母HTR-11在38℃下对酶解液进行乙醇发酵,质量浓度95.3 g/L的葡萄糖在18 h内发酵生成质量浓度为45.7 g/L的乙醇,其得率达到理论值的94%。     

Browsing Damage on Pine (Pinus sylvestris and P. contorta) by a migrating moose (Alces alces) Population in Winter: Relation to Habitat Composition and Road Barriers

In Scandinavia, moose (Alces alces L.) sometimes cause severe browsing damage to economically-important pine. Moose-vehicle accidents have spurred construction of fences along roads, and these may interfere with moose migration between summer and winter ranges, or the road alone may be a barrier. If this happens and moose build up along roads, landowners may suffer economically. Therefore, this study investigated whether roads, fences or other factors influence the use of young pine stands by moose. Eighty stands along roads in northern Sweden were evaluated in which individually-browsed branches were counted on 9972 pines. Moose browsing was not significantly related to birch (Betula pendula Roth, B. pubescens Ehrh.) density, nor did it differ between pines (Pinus contorta Douglas or P. sylvestris L.). However, increased pine density, site productivity and proximity to a highway were associated with increased browsing. Further large-scale studies are needed to understand moose habitat selection and the effects of roads.     

Effects of Root Freezing on the Physiology and Growth of Picea glauca,Picea mariana and Pinus banksiana Seedlings Under Different Soil Moisture Regimes

The root systems of 2-yr-old Picea glauca, Picea mariana and Pinus banksiana seedlings were submitted to various frost temperatures during an artificial frost to induce different levels of root damage. Frost-damaged and control seedlings were placed in a greenhouse under high and low soil moisture regimes. Seedling growth and physiology were evaluated periodically. Seedling survival was reduced when root damage reached levels of 60-80%. Root systems of all three species showed partial to total recovery by the end of the experiment. In general, root freezing damage caused reductions in seedling growth, with these reductions becoming less significant over time. Root damage had little to no effect on black spruce and jack pine seedling physiology, while white spruce CO 2 uptake decreased with increasing root damage. Shoot nitrogen content of all three species decreased slightly with increasing root damage.     

Decomposition and nutrient loss from prunings of different contour hedgerow species in tea plantations in the sloping highlands of Sri Lanka

Contour hedgerows of multipurpose tree species in the sloping tea lands of Sri Lanka are expected to reduce soil erosion and also add significant amounts of plant nutrients to the soil via periodic prunings. The objective of this experiment was to characterize the biomass decomposition pattern and quantify the amount of nutrients added through prunings of six tree species (Calliandra calothyrsus, Senna spectabilis, Euphatorium innulifolium, Flemingia congesta, Gliricidia sepium and Tithonia diversifolia) currently being used in hedgerows associated with tea. Withered leaf and stem prunings (50 g) were enclosed in 2-mm litter bags, placed at 5-cm depth and retrieved after one, three, six, nine and 12 weeks. Loss of initial dry weight, N, P and K was measured. Single exponential decay function adequately described both dry weight and nutrient loss. Tree species differed significantly in their rate of breakdown with decomposition constants (k) varying from 0.0299 to 0.2006 week⁻¹ for leaves and from 0.0225 to 0.0633 week⁻¹ for stems. Gliricidia showed the highest k for leaves with the rest in the following descending order: Senna > Tithonia ≥ Euphatorium > Calliandra > Flemingia. A similar pattern was observed for loss of all nutrients with Calliandra and Flemingia always having lower k values than the rest. Although N immobilization was not observed, immobilization of P and K was observed during the first week of incubation in some species, particularly in stem prunings. Annual biomass of prunings differed significantly between tree species in the following descending order: Calliandra > Senna > Flemingia > Tithonia > Gliricidia > Euphatorium. Calliandra added the greatest amount of nutrients annually to the soil with Euphatorium adding the least. Calliandra prunings provided the annual total K requirement and 49% of the N requirement of mature tea. However, none of the species provided more than 5% of the P requirement. It is concluded that among the tree species tested, Calliandra and Flemingia are the most suitable for contour hedgerows in tea plantations of this agroclimatic region because of their higher soil nutrient enrichment capacity and slower decomposition rates which would minimize leaching losses. This revised version was published online in June 2006 with corrections to the Cover Date.     

Effects of Seed Weight and Seed Type on Early Seedling Growth of Pinus sylvestris under Harsh and Optimal Conditions

The effects of seed weight and seed type on seedling growth of Pinus sylvestris (L.) were studied by seeding individually weighed orchard and stand seed in different mixtures under harsh (direct seeding in field) and optimal (seeding in nursery) conditions. In the nursery experiment an increase in the seed weight from 3 to 7 mg increased the seedling height by 10-27% and total weight by 27-113%, and decreased the height/diameter ratio by 5-6% after 2 yrs. With elimination of seed weight effects, orchard seedlings were 2% taller than stand seedlings in year 2. Without elimination of seed weight effects, orchard seedlings were 7-13% taller. In the field experiment an increase in the seed weight from 3 to 7 mg increased seedling height by 18-65%, stem volume by 81-274% and the number of top-buds by 23-34% in year 5. After elimination of seed weight effects, orchard seedlings were 7-13% taller than stand seedlings and without elimination of seed weight effects 20-21% taller after 5 yrs. Even after elimination of both seed weight and genetic effects orchard seedlings were 3-9% larger than stand seedlings in the field experiment. In conclusion, the influence of seed weight and seed type on growth traits and slenderness is highly significant and the influence seems to be greater in harsh conditions.     

Modelling of adequate pretwist for obtaining straight timber

Abstract

Wood in general and wooden studs in particular are often distorted owing to uneven shrinkage during the drying process in the sawmill. Twist is often the most detrimental of all types of distortion, and it is caused by spiral grain in combination with variations in moisture content. For sawmills, the objective is to produce dried, straight boards, and one method of dealing with boards with excessive spiral grain is to sort them out and then dry them in a pretwisted position to obtain straight boards after drying. A model using the finite element (FE) method for the simulation of drying twist distortions was first calibrated against laboratory experiments in which boards were dried with and without restraints and pretwists. After the calibration, the FE results were compared with industrial test results for boards that were dried without restraints or with restraints with zero pretwist, i.e. straight restraints. The FE model used an elastic–ideally plastic material model to obtain permanent deformations. The calibration was to set the yield stresses so that there was a good match between FE results and results from the laboratory experiments. The comparison between the industrial test results and the FE results showed that the FE model is capable of realistic simulations of drying boards with and without restraints and presumably also pretwists.     

Potential to harness superior nutritional qualities of exotic baobabs if local adaptation can be conferred through grafting

Baobab leaves form an important part of the local diet in Sahel countries and elsewhere in Africa. Existing leaf nutritional data and agroforestry performance information are based solely on Adansonia digitata L., the baobab of continental Africa. The introduction potential of Adansonia species from the center of diversity in Madagascar and from Australia remains untapped. To assess this potential, the mineral contents and B₁ and B₂ vitamin levels of dried baobab leaves were determined for five-year old trees of A. digitata, A. gibbosa (A. Cunn.) Guymer ex D. Baum, A. rubrostipa Jum. & H. Perrier (syn. A. fony Baill.), A. perrieri Capuron and A. za Baill. grown in an introduction trial in Mali. Nutritional data were evaluated against survival and vigor to identify promising germplasm. Leaf vitamin and crude protein contents were highest in the Madagascar species, especially A. rubrostipa (B₁ 88 mg 100 g⁻¹, B₂ 187 mg 100 g⁻¹, protein 20.7% dry weight). However, the local species far outperformed the introductions in survival, tree height, basal diameter and resistance to termites. We suggest grafting as a way of harnessing the vigor of well-adapted local baobab varieties to the superior nutritional profiles of A. rubrostipa and others. Cross-species grafting tests in Adansonia were successful, thus creating new agroforestry possibilities with different scion/rootstock combinations.     

Growth of Phlebiopsis gigantea in wood of seven conifer species

Heterobasidion parviporum and Heterobasidion annosum are widely distributed root‐rot fungi that infect conifers throughout Europe. Infection of conifer stumps by spores of these pathogens can be controlled by treating fresh stumps with a competing non‐pathogenic fungus, Phlebiopsis gigantea. In this study, growth of three Latvian strains of P. gigantea and the biological control agent ‘Rotstop’ strain was evaluated in stem pieces of Norway spruce, Scots pine, lodgepole pine, Douglas‐fir, Weymouth pine, Siberian larch and Sitka spruce. The growth rates of one H. parviporum and one H. annosum isolate were also measured in the same stem pieces. The growth rate of P. gigantea varied greatly in wood of different conifer species. It was higher in the three pine species, lower in Norway spruce and lowest in Sitka spruce and Siberian larch, and in Douglas‐fir, this fungus did not grow. The largest area of wood occupied by P. gigantea was in lodgepole pine. Growth of Latvian isolates of P. gigantea in the wood of Pinus and Picea species was comparable to that of the Rotstop isolate. Consequently, stump treatment with local P. gigantea isolates should be recommended. However, our results suggest that Douglas‐fir stump treatment against Heterobasidion by P. gigantea may be ineffective and other stump treatment methods should be considered.     

Stand Structure in Pine,Spruce and Deciduous Forests: A Comparison Between Finnish and Russian Karelia

This study investigated the stand structure in pine, spruce and deciduous forests in the border district of Finland and Russia. A total of 46 mature forest stands was selected as pairs, the members of each pair being as similar as possible with respect to their forest site type, age, moisture and topography. The stands were then compared between the two countries by means of basal areas and number of stems. The proportions of dominating tree species were 2-12% lower, and correspondingly the proportions of secondary tree species higher, in Russian forests. The density of the forest stock was also higher in each forest type in Russia. The forests in the two countries differed most radically in terms of the abundance of dead trees. The amount was two to four times higher in Russian deciduous and spruce forests, and in pine forests the difference was 10-fold. The stand structures indicated that Russian coniferous stands, in particular, were more heterogeneous than intensively managed pine and spruce stands in Finland.     

Growth and Terminal Bud Formation in Picea abies Seedlings Grown with Alternating Diurnal Temperature and Different Light Qualities

The root collar diameter and the height:diameter ratio are of particular importance in container-grown seedlings where a high density in the containers may produce spindly seedlings. Temperature regimes and light quality are known to affect plant growth. The aim of this study was to identify responses in Picea abies (L.) Karst. seedlings grown with light providing different red:far-red ratios and under temperature regimes with alternating day (DT) and night temperature (NT) from negative (DT < NT) to positive (DT > NT) difference (DIF) between DT and NT. Experiments were conducted in controlled environment chambers and in a daylight phytotron. Only limited thermoperiodic responses appeared in P . abies seedlings with respect to seedling height and dry weight accumulation. The formation of terminal buds, however, was clearly delayed in seedlings grown at negative DIF. The results indicate a requirement for day extension light that is high in far-red, to prevent terminal bud formation under natural short-day conditions. An extended study should be conducted to clarify the minimum level of light intensity and the optimal light quality needed to prevent terminal bud formation under natural short-day conditions.     

CAD与建筑设计的关系

本文分析了CAD在设计中引起的正面和负面影响,并进行了系统的阐述,从而使设计者在应用中能够保持客观的态度。