Poplar genetic engineering: promoting desirable wood characteristics and pest resistance

Worldwide biomass demand for industrial applications, especially for production of biofuels, is increasing. Extended cultivation of fast growing trees such as poplars may contribute to satisfy the need for renewable resources. However, lignin, which constitutes about 20–30 % of woody biomass, renders poplar wood recalcitrant to saccharification. Genetic engineering of the enzymes of the lignification pathway has resulted in drastic decreases in lignin and greatly improved the carbohydrate yield for ethanol fermentation. While uncovering key enzymes for lignification facilitated rapid biotechnological progress, knowledge on field performance of low-lignin poplars is still lagging behind. The major biotic damage is caused by poplar rust fungi (Melampsora larici-populina), whose defense responses involve lignification and production of phenolic compounds. Therefore, manipulation of the phenylpropanoid pathway may be critical and should be tightly linked with new strategies for improved poplar rust tolerance. Emerging novel concepts for wood improvement are discussed.     

Biogenic vs. geologic carbon emissions and forest biomass energy production

In the current debate over the CO₂ emissions implications of switching from fossil fuel energy sources to include a substantial amount of woody biomass energy, many scientists and policy makers hold the view that emissions from the two sources should not be equated. Their rationale is that the combustion or decay of woody biomass is simply part of the global cycle of biogenic carbon and does not increase the amount of carbon in circulation. This view is frequently presented as justification to implement policies that encourage the substitution of fossil fuel energy sources with biomass. We present the opinion that this is an inappropriate conceptual basis to assess the atmospheric greenhouse gas (GHG) accounting of woody biomass energy generation. While there are many other environmental, social, and economic reasons to move to woody biomass energy, we argue that the inferred benefits of biogenic emissions over fossil fuel emissions should be reconsidered.     

Renewable Energy from Willow Biomass Crops: Life Cycle Energy,Environmental and Economic Performance

Short-rotation woody crops (SRWC) along with other woody biomass feedstocks will play a significant role in a more secure and sustainable energy future for the United States and around the world. In temperate regions, shrub willows are being developed as a SRWC because of their potential for high biomass production in short time periods, ease of vegetative propagation, broad genetic base, and ability to resprout after multiple harvests. Understanding and working with willow's biology is important for the agricultural and economic success of the system.

The energy, environmental, and economic performance of willow biomass production and conversion to electricity is evaluated using life cycle modeling methods. The net energy ratio (electricity generated/life cycle fossil fuel consumed) for willow ranges from 10 to 13 for direct firing and gasification processes. Reductions of 70 to 98 percent (compared to U.S. grid generated electricity) in greenhouse gas emissions as well as NO_x, SO₂, and particulate emissions are achieved.

Despite willow's multiple environmental and rural development benefits, its high cost of production has limited deployment. Costs will be lowered by significant improvements in yields and production efficiency and by valuing the system's environmental and rural development benefits. Policies like the Conservation Reserve Program (CRP), federal biomass tax credits and renewable portfolio standards will make willow cost competitive in the near term.

The avoided air pollution from the substitution of willow for conventional fossil fuel generated electricity has an estimated damage cost of $0.02 to $0.06 kWh^?1. The land intensity of about 4.9 × 10^?5 ha-yr/kWh is greater than other renewable energy sources. This may be considered the most significant limitation of willow, but unlike other biomass crops such as corn it can be cultivated on the millions of hectares of marginal agricultural lands, improving site conditions, soil quality and landscape diversity. A clear advantage of willow biomass compared to other renewables is that it is a stock resource whereas wind and PV are intermittent. With only 6 percent of the current U.S. energy consumption met by renewable sources the accelerated development of willow biomass and other renewable energy sources is critical to address concerns of energy security and environmental impacts associated with fossil fuels.     

Optimal Locations for Methanol and CHP Production in Eastern Finland

Finland considers energy production from woody biomass as an efficient energy planning strategy to increase the domestic renewable energy production in order to substitute fossil fuel consumption and reduce greenhouse gas emissions. Consequently, a number of developmental activities are implemented in the country, and one of them is the installation of second generation liquid biofuel demonstration plants. In this study, two gasification-based biomass conversion technologies, methanol and combined heat and power (CHP) production, are assessed for commercialization. Spatial information on forest resources, sawmill residues, existing biomass-based industries, energy demand regions, possible plant locations, and a transport network of Eastern Finland is fed into a geographically explicit Mixed Integer Programming model to minimize the costs of the entire supply chain which includes the biomass supply, biomass and biofuel transportation, biomass conversion, energy distribution, and emissions. The model generates a solution by determining the optimal number, locations, and technology mix of bioenergy production plants. Scenarios were created with a focus on biomass and energy demand, plant characteristics, and cost variations. The model results state that the biomass supply and high energy demand are found to have a profound influence on the potential bioenergy production plant locations. The results show that methanol can be produced in Eastern Finland under current market conditions at an average cost of 0.22??/l with heat sales (0.34??/l without heat sales). The introduction of energy policy tools, like cost for carbon, showed a significant influence on the choice of technology and CO₂ emission reductions. The results revealed that the methanol technology was preferred over the CHP technology at higher carbon dioxide cost (>145??/t_CO2). The results indicate that two methanol plants (360?MW_biomass) are needed to be built to meet the transport fuel demand of Eastern Finland.     

Enzymatic hydrolysis of biomass from wood

Current research and development in cellulosic ethanol production has been focused mainly on agricultural residues and dedicated energy crops such as corn stover and switchgrass; however, woody biomass remains a very important feedstock for ethanol production. The precise composition of hemicellulose in the wood is strongly dependent on the plant species, therefore different types of enzymes are needed based on hemicellulose complexity and type of pretreatment. In general, hardwood species have much lower recalcitrance to enzymes than softwood. For hardwood, xylanases, beta‐xylosidases and xyloglucanases are the main hemicellulases involved in degradation of the hemicellulose backbone, while for softwood the effect of mannanases and beta‐mannosidases is more relevant. Furthermore, there are different key accessory enzymes involved in removing the hemicellulosic fraction and increasing accessibility of cellulases to the cellulose fibres improving the hydrolysis process. A diversity of enzymatic cocktails has been tested using from low to high densities of biomass (2–20% total solids) and a broad range of results has been obtained. The performance of recently developed commercial cocktails on hardwoods and softwoods will enable a further step for the commercialization of fuel ethanol from wood.     

Pretreatment of woody biomass for biofuel production: energy efficiency, technologies, and recalcitrance

This mini review discusses several key technical issues associated with cellulosic ethanol production from woody biomass: energy consumption for woody biomass pretreatment, pretreatment energy efficiency, woody biomass pretreatment technologies, and quantification of woody biomass recalcitrance. Both total sugar yield and pretreatment energy efficiency, defined as the total sugar recovery divided by total energy consumption for pretreatment, should be used to evaluate the performance of a pretreatment process. A post-chemical pretreatment wood size-reduction approach was proposed to significantly reduce energy consumption. The review also emphasizes using a low liquid-to-wood ratio (L/W) to reduce thermal energy consumption for any thermochemical/physical pretreatment in addition to reducing pretreatment temperature.     

Challenges of the utilization of wood polymers: how can they be overcome?

Diminishing fossil fuel resources as well as growing environmental and energy security concerns, in parallel with growing demands on raw materials and energy, have intensified global efforts to utilize wood biopolymers as a renewable resource to produce biofuels and biomaterials. Wood is one of the most abundant biopolymer composites on earth that can be converted into biofuels as well as used as a platform to produce bio-based materials. The major biopolymers in wood are cellulose, hemicelluloses, and lignin which account for >90% of dry weight. These polymers are generally associated with each other in wood cell walls resulting in an intricate and dynamic cell wall structure. This mini-review provides an overview of major wood biopolymers, their structure, and recent developments in their utilization to develop biofuels. Advances in genetic modifications to overcome the recalcitrance of woody biomass for biofuels are discussed and point to a promising future.     

Water-based woody biorefinery

The conversion of biomass into chemicals and energy is essential in order to sustain our present way of life. Fossil fuels are currently the predominant energy source, but fossil deposits are limited and not renewable. Biomass is a reliable potential source of materials, chemicals and energy that can be replenished to keep pace with our needs. A biorefinery is a concept for the collection of processes used to convert biomass into materials, chemicals and energy. The biorefinery is a “catch and release” method for using carbon that is beneficial to both the environment and the economy. In this study, we discuss three elements of a wood-based biorefinery, as proposed by the SUNY College of Environmental Science and Forestry (ESF): hot-water extraction, hydrolysis, and membrane separation/concentration. Hemicelluloses are the most easily separable main component of woody biomass and thus form the bulk of the extracts obtained by hot-water extraction of woody biomass. Hot-water extraction is an important step in the processes of woody biomass and product generation, replacing alternative costly pre-treatment methods. The hydrolysis of hemicelluloses produces 5-carbon sugars (mainly xylose), 6-carbon sugars (mainly glucose and mannose), and acetic acid. The use of nano-filtration membranes is an efficient technology that can be employed to fractionate hot-water extracts and wood hydrolysate. The residual solid mass after hot-water extraction has a higher energy content and contains fewer easily degradable components. This allows for more efficient subsequent processing to convert cellulose and lignin into conventional products.     

A sustainable woody biomass biorefinery

Woody biomass is renewable only if sustainable production is imposed. An optimum and sustainable biomass stand production rate is found to be one with the incremental growth rate at harvest equal to the average overall growth rate. Utilization of woody biomass leads to a sustainable economy. Woody biomass is comprised of at least four components: extractives, hemicellulose, lignin and cellulose. While extractives and hemicellulose are least resistant to chemical and thermal degradation, cellulose is most resistant to chemical, thermal, and biological attack. The difference or heterogeneity in reactivity leads to the recalcitrance of woody biomass at conversion. A selection of processes is presented together as a biorefinery based on incremental sequential deconstruction, fractionation/conversion of woody biomass to achieve efficient separation of major components. A preference is given to a biorefinery absent of pretreatment and detoxification process that produce waste byproducts. While numerous biorefinery approaches are known, a focused review on the integrated studies of water-based biorefinery processes is presented. Hot-water extraction is the first process step to extract value from woody biomass while improving the quality of the remaining solid material. This first step removes extractives and hemicellulose fractions from woody biomass. While extractives and hemicellulose are largely removed in the extraction liquor, cellulose and lignin largely remain in the residual woody structure. Xylo-oligomers, aromatics and acetic acid in the hardwood extract are the major components having the greatest potential value for development. Higher temperature and longer residence time lead to higher mass removal. While high temperature (>200°C) can lead to nearly total dissolution, the amount of sugars present in the extraction liquor decreases rapidly with temperature. Dilute acid hydrolysis of concentrated wood extracts renders the wood extract with monomeric sugars. At higher acid concentration and higher temperature the hydrolysis produced more xylose monomers in a comparatively shorter period of reaction time. Xylose is the most abundant monomeric sugar in the hydrolysate. The other comparatively small amounts of monomeric sugars include arabinose, glucose, rhamnose, mannose and galactose. Acetic acid, formic acid, furfural, HMF and other byproducts are inevitably generated during the acid hydrolysis process. Short reaction time is preferred for the hydrolysis of hot-water wood extracts. Acid hydrolysis presents a perfect opportunity for the removal or separation of aromatic materials from the wood extract/hydrolysate. The hot-water wood extract hydrolysate, after solid-removal, can be purified by Nano-membrane filtration to yield a fermentable sugar stream. Fermentation products such as ethanol can be produced from the sugar stream without a detoxification step.     

Energy production from biomass (Part 2): Conversion technologies

The use of biomass to provide energy has been fundamental to the development of civilisation. In recent times pressures on the global environment have led to calls for an increased use of renewable energy sources, in lieu of fossil fuels. Biomass is one potential source of renewable energy and the conversion of plant material into a suitable form of energy, usually electricity or as a fuel for an internal combustion engine, can be achieved using a number of different routes, each with specific pros and cons. A brief review of the main conversion processes is presented, with specific regard to the production of a fuel suitable for spark ignition gas engines.     

Energy production from biomass (Part 1): Overview of biomass

The use of renewable energy sources is becoming increasingly necessary, if we are to achieve the changes required to address the impacts of global warming. Biomass is the most common form of renewable energy, widely used in the third world but until recently, less so in the Western world. Latterly much attention has been focused on identifying suitable biomass species, which can provide high-energy outputs, to replace conventional fossil fuel energy sources. The type of biomass required is largely determined by the energy conversion process and the form in which the energy is required. In the first of three papers, the background to biomass production (in a European climate) and plant properties is examined. In the second paper, energy conversion technologies are reviewed, with emphasis on the production of a gaseous fuel to supplement the gas derived from the landfilling of organic wastes (landfill gas) and used in gas engines to generate electricity. The potential of a restored landfill site to act as a biomass source, providing fuel to supplement landfill gas-fuelled power stations, is examined, together with a comparison of the economics of power production from purpose-grown biomass versus waste-biomass. The third paper considers particular gasification technologies and their potential for biomass gasification.     

Net change in carbon emissions with increased wood energy use in the United States

Use of wood biomass for energy results in carbon (C) emissions at the time of burning and alters C stocks on the land because of harvest, regrowth, and changes in land use or management. This study evaluates the potential effects of expanded woody biomass energy use (for heat and power) on net C emissions over time. A scenario with increased wood energy use is compared with a dynamic business-as-usual scenario where wood energy use is driven by its historical relationship with gross domestic product. At the national level, we projected that up to 78% of increased cumulative C emissions from increased wood burning and up to 80% of increased cumulative radiative forcing would be offset over 50 years by change in forest area loss, biomass regrowth on land, C storage in harvested wood products, and C in logging slash left in forests. For example, forest area is projected to decline in both scenarios, but 3.5 million hectares more are retained in the high wood energy-use case. Projected C offsets over a 50 year period differed substantially by US region (16% in the North, 50% in the West, and 95% in the South) not only because of differences in forest regrowth and induced investment in retaining and planting forest, but also because of shifts in competitive advantage among regions in producing various wood products. If wood systems displace coal systems that have 75% of the C emissions of wood energy systems per unit energy, then the nationwide net C emissions offset would be reduced to 71–74%. If displacing natural gas systems that have 40% of the level of wood bioenergy emissions per unit energy, the nationwide net C emissions offset would be 46–52%.     

中国如何突破生物柴油产业的原料瓶颈

因应我国日益严峻的能源资源、能源环境和能源安全形势,国家大力倡导发展可再生能源。生物柴油是最重要的液体可再生燃料之一,在能源性质方面可以完全替代化石柴油,而且还具有安全环保等其它优良特性。当前利用动植物油脂生产生物柴油,原料成本偏高,而且稳定、充足的油脂原料供应体系尚未形成。我国是油脂资源短缺国家,近年来植物油进口量逐年增加。同时,我国耕地资源匮乏,粮食供应形势不容乐观,扩大油料作物种植的潜力非常有限。但是,我国宜林地丰富,农林废弃生物质资源量巨大。综合以上因素,我国应重点发展木本油料植物规模化种植和推广,加快微生物油脂发酵技术创新和产业化进程;同时,利用植物遗传育种技术提高油料作物产量以及选择性发展不与粮争地的油料作物。依靠各方面的进步,发展创新的油脂生产技术,保障我国生物柴油产业和油脂化工行业健康发展。     

Dead wood biomass and turnover time,measured by radiocarbon,along a subalpine elevation gradient

Dead wood biomass can be a substantial fraction of stored carbon in forest ecosystems, and coarse woody debris (CWD) decay rates may be sensitive to climate warming. We used an elevation gradient in Colorado Rocky Mountain subalpine forest to examine climate and species effects on dead wood biomass, and on CWD decay rate. Using a new radiocarbon approach, we determined that the turnover time of lodgepole pine CWD (340±130 years) was roughly half as long in a site with 2.5–3°C warmer air temperature, as that of pine (630±400 years) or Engelmann spruce CWD (800±960 and 650±410 years) in cooler sites. Across all sites and both species, CWD age ranged from 2 to 600 years, and turnover time was 580±180 years. Total standing and fallen dead wood biomass ranged from 4.7±0.2 to 54±1 Mg ha^–1, and from 2.8 to 60% of aboveground live tree biomass. Dead wood biomass increased 75 kg ha^–1 per meter gain in elevation and decreased 13 Mg ha^–1 for every degree C increase in mean air temperature. Differences in biomass and decay rates along the elevation gradient suggest that climate warming will lead to a loss of dead wood carbon from subalpine forest.Electronic Supplementary Material Supplementary material is available for this article at     

Biotechnology in the wood industry

Wood is a natural, biodegradable and renewable raw material, used in construction and as a feedstock in the paper and wood product industries and in fuel production. Traditionally, biotechnology found little attention in the wood product industries, apart from in paper manufacture. Now, due to growing environmental concern and increasing scientific knowledge, legal restrictions to conventional processes have altered the situation. Biotechnological approaches in the area of wood protection aim at enhancing the treatability of wood with preservatives and replacing chemicals with biological control agents. The substitution of conventional chemical glues in the manufacturing of board materials is achieved through the application of fungal cultures and isolated fungal enzymes. Moreover, biotechnology plays an important role in the waste remediation of preservative-treated waste wood.     

能量效率与可更新能源

一可更新能源可减少甚至消除我们对化石能和核能的依赖,其中很多虽然已为人类使用数百年,但因为石能的普遍使用,一直都为起人类的注意。人类已发明了新技术利用这些可更新能源。其利用不赖于一定的技术是既定的事实,目前有成功建立这样的能源工业还是十分昂贵的。如果人类生产经济和市场允许的话,这些新的技术经进一步改进和简化后,就可以降低成本,并且应用起来也很可靠。相对于开发应用核能,水能和化石能数以百万计的投资耗费来讲,用于可更新资源的资金可谓微乎其微。虽然传统能源和替代能源各具优点,但保护能源往往还是解决能源短缺最便宜,最容易的途径。     

能量效率与可更新能源

一些可更新能源可减少甚至消除我们对化石能和核能的依赖,其中很多虽然已为人类使用数百年,但因为化石能的普遍使用,一直都为起人类的注意。人类已发明了新技术来利用这些可更新能源。其利用有赖于一定的技术是既定的事实,目前有成功建立这样的能源工业还是十分昂贵的。如果人类生产经济和市场允许的话,这些新技术经进一步改进和简化后,就可以降低成本,并且应用起来也很可靠。相对于开发应用核能,水能和化石能数以百万计的投资耗费来讲,用于可更新资源的资金可谓微乎其微。虽然传统能源和替代能源各具优点,但保护能源往往还是解决能源短缺最便宜,最容易的途径。     

Tree structure,regeneration and woody biomass removal in a sub-tropical forest of Mamlay watershed in the Sikkim Himalaya

This paper reports on the tree structure, tree dimension relationships and woody biomass production and removal of a sub-tropical natural forest in the Mamlay watershed of the Sikkim Himalaya. The forest provides fuel, fodder and timber to four villages. Only 11 tree species were found growing in the tree stratum despite the high diversity in the stand (32 tree species). The forest shows good regeneration potential with 5474 seedlings/ha and 1776 saplings/ha, but the population structure revealed a marked paucity of trees of higher diameter classes due to removal of trees of lower diameters. Standing wood biomass of 362 Mg/ha is mainly shared by 4 dominating species in the stand. The boles are removed mainly for timber and fuel purposes and about 22 Mg/ha wood biomass was removed in between 1987–1991. Net Primary productivity of woody biomass of the forest is recorded to be 18 Mg/ha/year. 3.85 Mg/ha of annual woody biomass production was removed in the form of tree boles apart from lopping of branches.