4种木质纤维素预处理方法的比较

采用4种方法对玉米秸秆预处理,研究了不同预处理方法对酶水解性能和可发酵性糖得率的影响,分析了预处理物料主要成分,预水解液中糖组成、碳水化合物降解产物及木质素降解产物含量.100 g玉米秸秆经稀酸、稀酸磨浆、中性蒸汽爆破和稀酸蒸汽爆破预处理、洗涤后,物料中纤维素由37.17g分别降为33.96、33.54、32.63和32.88 g,木聚糖由22.84 g分别降为2.77、2.47、3.56和2.05 g,木质素由18.76 g分别降为17.63、17.42、16.90和17.25 g.稀酸蒸汽爆破预处理物料在底物质量浓度100 g/L、纤维素酶用量20 FPIU/g(以纤维素计,下同)、β-葡萄糖苷酶用量3 IU/g下酶水解48 h,纤维素水解得率为75.91％.玉米秸秆经稀酸蒸汽爆破预处理、纤维素酶水解后可发酵性糖得率为44.93％(以玉米秸秆为基准).     

几种纤维素酶制剂水解和吸附性能的研究

比较了商品纤维素酶和自产纤维素酶在蛋白组分及蛋白组分含量上存在的差异。商品纤维素酶水解稀酸预处理和蒸汽爆破预处理的玉米秸秆,其水解得率均低于自产纤维素酶。以蒸汽爆破的玉米秸秆为碳源制备纤维素酶,添加外源8 IU/g(以纤维素计)的β-葡萄糖苷酶,水解蒸汽爆破的玉米秸秆48 h,纤维素水解得率为90.08%;水解液中纤维二糖的质量浓度从17.06 g/L降低到1.12 g/L,相应葡萄糖质量浓度从21.09 g/L提高到44.01 g/L,可发酵性糖从55.28%提高到97.52%。微晶纤维素对商品酶和自产酶的吸附在30 m in达到平衡,且符合Langmu ir等温吸附方程;由Langmu ir常数分析得知两类酶均来自里氏木霉,且对微晶纤维素的亲和力相差不大。     

稀硫酸-氢氧化钙联合预处理玉米秸秆制乙醇

以玉米秸秆为原料,研究稀硫酸-氢氧化钙联合预处理秸秆制备燃料乙醇的方法。玉米秸秆经稀硫酸预处理、固液分离后得到的预水解液(主要含有木糖)进行戊糖发酵;而残渣采用氢氧化钙进一步预处理后,经酶水解得到的葡萄糖进行己糖发酵,从而实现戊糖和己糖分开发酵产乙醇。研究结果表明,玉米秸秆稀硫酸预处理最佳条件为:硫酸用量1.00%(以绝干玉米秸秆计),反应温度130℃,反应时间70 min,此时木聚糖水解得率为80.45%;采用树干毕赤酵母对玉米秸秆稀硫酸预水解液原液、浓缩液Ⅰ(浓度为原液的2倍)和浓缩液Ⅱ(浓度为原液的3.5倍)进行戊糖发酵,乙醇得率分别为82.52%、85.13%和73.64%。氢氧化钙进一步预处理玉米秸秆稀硫酸预处理渣的最佳条件为:氢氧化钙用量0.125 g/g(以绝干玉米秸秆计),反应温度90℃,时间24 h,此时纤维素酶水解得率为84.92%;采用酿酒酵母对两步预处理残渣的酶水解液原液、浓缩液Ⅲ和浓缩液Ⅳ(浓度为原液的2倍和3倍)进行己糖发酵,乙醇得率分别为92.22%、91.89%和85.54%。     

绿液预处理麦秆纤维素酶水解的研究

研究了绿液预处理对麦秆酶水解的影响.比较了不同绿液预处理条件下麦秆的浆得率、成分组成与纤维素酶解率,结果表明,预处理条件越剧烈,原料损失越大,而木质素脱除率越高,且在相同酶水解条件下,纤维素酶解率却越高,其中适宜的条件是预处理温度150℃,总碱量8％(Na2O计,对绝干原料)和硫化度40％,浆得率62.0％,葡聚糖、木聚糖和木质素质量分数50.0％、18.9％和16.2％,葡萄糖和木糖得率分别为74.2％和73.5％.考察了质量浓度和酶用量对绿液预处理麦秆酶水解的影响,优化了商品纤维素酶酶系结构和Tween-80的添加量,表明绿液预处理麦秆纤维素酶水解的适宜条件为质量浓度100 g/L,纤维素酶用量15 FPU/g(以纤维素计,下同),β-葡萄糖苷酶9 IU/g,木聚糖酶30 IU/g,Tween-800.05 g/g.在以上条件下,酶水解72 h,葡萄糖得率和木糖得率分别达到了82.5％和77.8％,是优化前的2.6和1.6倍.     

稀酸预处理玉米秸秆共发酵产乙醇抑制物的来源探究

针对己糖(葡萄糖)、戊糖(木糖)共发酵产纤维素乙醇抑制物控制的关键性瓶颈,分别以玉米秸秆及玉米秸秆中非木质素的4类组分纤维素、半纤维素、热水提取物和乙醇提取物为原料,并以0.75%稀硫酸和180℃预处理40 min得到5种稀酸预处理液。以60 g/L葡萄糖和30 g/L木糖为碳源,分别添加上述稀酸预处理液,比较了5种预处理液对休哈塔假丝酵母(Candida shehatae)共发酵产乙醇的影响,并探究主要抑制物来源。结果表明:133 g/L全玉米秸秆稀酸预处理的降解物会完全抑制C.shehatae糖代谢和共发酵。在玉米秸秆稀酸预处理过程中,4类非木质素组分降解物均会导致乙醇得率下降,其中100 g/L纤维素降解物完全抑制木糖的发酵,半纤维素降解物同时抑制葡萄糖和木糖的发酵,甚至对酵母产生致死毒性,热水提取物和乙醇提取物降解物延滞糖利用和酵母生长。玉米秸秆共发酵产乙醇抑制物主要来自于纤维素和半纤维素在稀酸预处理中的降解反应,主要为甲酸、乙酸、乙酰丙酸、5-羟甲基糠醛和糠醛,同时还存在着其他降解产物的毒性或协同毒性。     

稀酸预处理改善玉米秸秆酶水解性能的机制探讨

为了探讨在稀酸预处理提高玉米秸秆在纤维素酶酶解阶段提高纤维素转化率的机制,利用一系列的检测方法:FT-IR、XRD、SEM和比表面积分析仪分析了预处理前后玉米秸秆在形态学和物理化学性质方面的变化.在经过稀酸预处理后的玉米秸秆在纤维素酶酶解阶段其纤维素转化率有较大的提高,经过170℃,60 min,固液比1∶15(g∶mL),1.00 g/mL酸质量浓度的条件预处理后,从31.88％提高到95.74％.XRD结果显示预处理后玉米秸秆的结晶度有所增加,从原料的37.8％增加到58.7％,但是当预处理强度增加到一定程度后,结晶度没有较大的变化,基本维持在58％.玉米秸秆的表面结构在稀酸预处理后,原来的光滑表面变得粗糙、多孔,这样的表面有利于纤维素酶与玉米秸秆的接触,预处理后玉米秸秆的比表面积有很大程度的增加,经过170℃,60 min,固液比1∶15,1.00g/mL酸质量浓度的条件预处理后,玉米秸秆的比表面积从0.329 m2/g增加到2.878 m2/g,这都有利于改善纤维素酶对纤维素的作用,增加纤维素转化率.     

木质素基表面活性剂对玉米秸秆纤维素酶水解的促进作用

木质素是影响木质纤维原料酶水解的关键因素。本研究通过聚乙氧基接枝修饰制备木质素基表面活性剂,并探究其对预处理玉米秸秆纤维素酶水解的影响机制。结果表明,木质素基表面活性剂对蒸汽爆破预处理玉米秸秆酶水解有显著的促进作用。木质素基表面活性剂的最适添加量为0025 0 g/g(以纤维素计)。在最适添加量下,碱木质素基表面活性剂及醇溶木质素基表面活性剂使得蒸汽爆破预处理玉米秸秆72 h酶水解得率分别提高了275%和281%。与此同时,72 h酶水解液中外切葡聚糖酶酶活力分别提高了493%和410%;β-葡萄糖苷酶酶活力分别提高了196%和137%。说明木质素基表面活性剂可减少纤维素酶的无效吸附,从而起到对酶水解的促进作用。     

低浓度乙酸预处理玉米芯的工艺研究

以脱除木质素,降解半纤维素为木糖,提高纤维素酶解得率为目的,研究了低浓度乙酸预处理玉米芯的效果,考察了乙酸质量分数、预处理温度和时间对预处理的影响。研究结果表明:质量分数5%乙酸预处理玉米芯可以脱除大部分的半纤维素和少部分木质素,预处理后的玉米芯具有较好的水解效果。低浓度乙酸预处理玉米芯最优条件为:预处理温度160℃,保温时间60 min,乙酸质量分数5%,固液比1∶8(g∶mL)。在此条件下,玉米芯固体渣回收率为53.75%,固体渣中纤维素保留率93.17%,半纤维素脱除率87.36%,木质素脱除率25.04%,预处理液中木糖质量浓度15.56 g/L。预处理后的玉米芯固体经72 h酶解,酶解得率为92.69%。     

亚硫酸氢盐预处理对玉米秸秆酶水解的影响

研究了亚硫酸氢钠对玉米秸秆进行预处理的条件,主要考察了亚硫酸氢钠用量、预处理温度和pH值对玉米秸秆酶水解效率的影响。结果表明:在温度180℃、保温30min时,随着亚硫酸氢钠用量的增加,木质素和半纤维素的溶出量增大,从而促进玉米秸秆预处理后底物的酶水解,当亚硫酸氢钠用量为7%时,酶水解转化率和葡萄糖得率分别为69.40%和62.44%;预处理温度越高,酶水解效率越高,温度190℃、保温30min时底物酶水解转化率达到了81.04%,葡萄糖得率71.91%;预处理pH值升高,酶水解效率相应增大,pH值在4.2～4.7之间时,酶解效率增加明显。     

蒸汽预处理玉米秸秆酶水解速率下降的因素分析

为评价导致纤维素酶水解速率下降的因素,以底物质量浓度为50 g/L葡聚糖及酶用量为20 FPIU/g滤纸酶活和10 IU/g β-葡萄糖苷酶活的蒸汽预处理玉米秸秆酶水解为研究对象,探讨了影响酶水解速率的潜在因素,包括物料反应性能、纤维素酶非特异性吸附、酶失活及终产物抑制。结果表明：酶用量40 FPIU/g条件下酶水解6 h及12 h后,蒸汽预处理玉米秸秆的物料反应性能分别下降了16.0%及23.7%,然而,在酶用量为20 FPIU/g时,物料反应性能的下降对酶水解速率的影响极其有限;酶解木质素的添加使得1 h酶解上清液中酶蛋白浓度降低了20.8%,但初始酶水解速率并未显著降低,即木质素对纤维素酶的非特异性吸附对酶水解速率影响不大;两段酶水解中纤维素酶的更新使得7h酶水解速率由一段酶水解中的1.30 g/(L·h)提高至1.83 g/(L·h);两段酶水解中终产物的去除则使得7 h酶水解速率提高至4.76 g/(L·h),是一段酶水解中7 h酶水解速率的3.66倍。综合而言,酶失活及终产物抑制对酶水解速率影响较大,其中终产物抑制是导致蒸汽预处理玉米秸秆酶水解速率降低的关键因素。     

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.     

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。     

Risk Perception Among Non-industrial Private Forest Owners

Based on an enquiry, risk perception among non-industrial private forest owners is described in relation to climate change and forestry hazards. Of the respondents, 11% took action to remedy the effects of climate change. Out of a given set, hazards were ranked according to each respondent's experience of recent substantial financial loss to the estate and in relation to his or her willingness to make investments aimed at risk reduction. For each hazard, the respondent assessed the risk in four classes ranging from very high to negligible risk. Six hazards were considered most problematic in all three aspects: browsing damage, falling timber prices, damage by wind, spruce bark beetle, root rot and pine weevil. A majority of the respondents claimed to take action to reduce the risk associated with at least one hazard, while 35% did not know whether they did. Excluding climate change, the need for decision support was the largest in relation to damage by wind owing to a combination of perceived high risk and a high level of ignorance in relation to whether risk-reducing measures were taken.     

Natural Regeneration in Clear-cuts: Effects of Scarification,Slash Removal and Clear-cut Age

The effects of soil scarification (mounding), slash removal and clear-cut age on the natural regeneration in clear-cuts was evaluated using data from four sites in southern Sweden. The treatments were carried out during a good seed and establishment year for birch ( Betula pubescens Ehrh. and B. pendula Roth). Scarification had the strongest positive effect on the density of naturally regenerated seedlings, especially in birch, but also in pine ( Pinus sylvestris L.) and spruce [ Picea abies (L.) Karst]. Slash removal had a positive effect on birch density. No statistically significant effect of clear-cut age was found. In addition, no statistically significant interactions between clear-cut age and scarification or slash removal were found. The ingrowth of field vegetation was the fastest in areas that were not scarified, less rapid in areas scarified on old clear-cuts, and the slowest after scarification in fresh clear-cuts. In conclusion, it may be possible to control the density of birch during a good establishment year for birch. If birch is desired, the best combination of treatments is to remove the slash and scarify; otherwise, these treatments should be avoided.     

Interactions in decomposition and N mineralization between tropical legume residue components

In situ produced plant residues contain a mixture of different plant components of varying quality. To assess synergistic or antagonistic interactions occurring during the decomposition and mineralization of such mixtures, individual plant parts (stems, leaves, leaf litter and roots) or the mixture of stems, leaves and leaf litter of the agroforestry species pigeonpea (Cajanus cajan) or of crop residues of peanut (Arachis hypogaea) or of the weed hairy indigo (Indigofera hirsuta) were incubated in pots for 19 weeks. Periodically, remaining plant residues were sieved out (>2 mm), weighed and N content as well as soil mineral N determined. Above- and below-ground residues of peanut decomposed fastest and showed the largest N release in agreement with their high N concentration and low-acid detergent fibre (ADF) : N ratio. Hairy indigo was hypothesized to be of lower quality than pigeonpea because of its high-polyphenol content. However, it decomposed faster than pigeonpea, largely because of the higher N and lower lignin concentration of its components. Ranking of individual plant components for N mineralization resulted in the following pattern, leaves > leaf litter > roots > stems. In mixtures of the different plant components a similar species order in decomposition was obtained, e.g. peanut > hairy indigo > pigeonpea. The amount of N released from the mixture was dominated by stem material that comprised 46–61% of the mixture. The interactions in mixtures were relatively small for peanut (generally high-quality components) as well as for pigeonpea (low proportion of high-quality components, i.e. N rich leaf material). However, a positive interaction occurred during later stages of N mineralization in the mixture of hairy indigo as it had a significant proportion of N rich components and absence of highly reactive polyphenols. Thus, for plants with low to intermediate chemical quality attributes, manipulating plant composition (e.g. by varying harvest age, affecting stem and leaf proportions) will be important to obtain significant interactions during decomposition when its components are mixed.     

Pasture production and tree growth in a young pine plantation fertilized with inorganic fertilizers and milk sewage in northwestern Spain

The use of organic waste materials such as milk sewage as an organic fertilizer could have the dual advantages of organic-waste disposal and reduced dependence on inorganic fertilizers. The effects of fertilization with (1) conventional mineral fertilization, (2) milk sewage sludge at 40 kg N ha⁻¹ target rate and (3) no fertilization on pasture production and tree growth were examined in an experiment consisting of two pasture mixtures under a one-year-old Pinus radiata plantation with a density of 2500 trees ha⁻¹. The two pasture mixtures were: (1) Dactylis glomerata L. var. saborto (25 kg ha⁻¹) + Trifolium repens L. group Ladino (4 kg ha⁻¹) + Trifolium pratense L. var. Marino (1 kg ha⁻¹); (2) Lolium perenne L. var. Tove (25 kg ha⁻¹) + Trifolium repens L. group Ladino (4 kg ha⁻¹) + Trifolium pratense L. var. Marino (1 kg ha⁻¹). The experiment began in the spring of 1995 using a randomized block design with three replicates in Castro Riberas de Lea (Lugo, Galicia, north-western Spain). Plot size was 12 × 8 m², with a 1 m buffer strip between plots. Two-year data showed that fertilization with either material had a positive effect on pasture production, with no significant difference between the two fertilization treatments. Tree growth in the milk sewage sludge plot was significantly higher than in the control plots. Inorganic fertilization increased pasture production, but affected tree growth negatively. The results show that milk sewage sludge could be used as a fertilizer in silvo-pastoral systems. This revised version was published online in June 2006 with corrections to the Cover Date.