Genetic improvement of willow for bioenergy and biofuels

Willows (Salix spp.) are a very diverse group of catkin-bearing trees and shrubs that are widely distributed across temperate regions of the globe. Some species respond well to being grown in short rotation coppice (SRC) cycles, which are much shorter than conventional forestry. Coppicing reinvigorates growth and the biomass rapidly accumulated can be used as a source of renewable carbon for bioenergy and biofuels. As SRC willows re-distribute nutrients during the perennial cycle they require only minimal nitrogen fertilizer for growth. This results in fuel chains with potentially high greenhouse gas reductions. To exploit their potential for renewable energy, willows need to be kept free of pests and diseases and yields need to be improved without significantly increasing the requirements for fertilizers and water. The biomass composition needs to be optimized for different end-uses. Yields also need to be sustainable on land less productive for food crops to reduce conflicts over land use. Advances in understanding the physiology and growth of willow, and in the identification of genes underlying key traits, are now at the stage where they can start to be used in breeding programs to help achieve these goals.     

Investment risk in bioenergy crops

Perennial, cellulosic bioenergy crops represent a risky investment. The potential for adoption of these crops depends not only on mean net returns, but also on the associated probability distributions and on the risk preferences of farmers. Using 6‐year observed crop yield data from highly productive and marginally productive sites in the southern Great Lakes region and assuming risk neutrality, we calculate expected breakeven biomass yields and prices compared to corn (Zea mays L.) as a benchmark. Next we develop Monte Carlo budget simulations based on stochastic crop prices and yields. The crop yield simulations decompose yield risk into three components: crop establishment survival, time to maturity, and mature yield variability. Results reveal that corn with harvest of grain and 38% of stover (as cellulosic bioenergy feedstock) is both the most profitable and the least risky investment option. It dominates all perennial systems considered across a wide range of farmer risk preferences. Although not currently attractive for profit‐oriented farmers who are risk neutral or risk averse, perennial bioenergy crops have a higher potential to successfully compete with corn under marginal crop production conditions.     

Management swing potential for bioenergy crops

Bioenergy crops are often classified (and subsequently regulated) according to species that have been evaluated as environmentally beneficial or detrimental, but in practice, management decisions rather than species per se can determine the overall environmental impact of a bioenergy production system. Here, we review the greenhouse gas balance and ‘management swing potential’ of seven different bioenergy cropping systems in temperate and tropical regions. Prior land use, harvesting techniques, harvest timing, and fertilization are among the key management considerations that can swing the greenhouse gas balance of bioenergy from positive to negative or the reverse. Although the management swing potential is substantial for many cropping systems, there are some species (e.g., soybean) that have such low bioenergy yield potentials that the environmental impact is unlikely to be reversed by management. High‐yielding bioenergy crops (e.g., corn, sugarcane, Miscanthus, and fast‐growing tree species), however, can be managed for environmental benefits or losses, suggesting that the bioenergy sector would be better informed by incorporating management‐based evaluations into classifications of bioenergy feedstocks.     

The battle of crops against drought: Genetic dissection and improvement

With ongoing global climate change,water scarcity-induced drought stress remains a major threat to agricultural productivity.Plants undergo a series of physiological and morphological changes to cope with drought stress,including stomatal closure to reduce transpiration and changes in root architecture to optimize water uptake.Combined phenotypic and multi-omics studies have recently identified a number of drought-related genetic resources in different crop species.The functional dissection of t...     

Energy and carbon accounting to compare bioenergy crops

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Highlights► Comparing biofuel crops is exceedingly difficult using conventional measurement methods. ► The PETRO approach quantitatively compares biological matter in terms of energy and carbon. ► Tracking carbon flux from air to liquid fuel compares all biofuel crop yields on a common basis. ► Reporting energy yields (GJ ha⁻¹ y⁻¹) and carbon flux (Mg_C ha⁻¹ y⁻¹) enables regional comparison.     

Sweet sorghum as a model system for bioenergy crops

Bioenergy is the reduction of carbon via photosynthesis. Currently, this energy is harvested as liquid fuel through fermentation. A major concern, however, is input cost, in particular use of excess water and nitrogen, derived from an energy-negative process, the Haber-Bosch method. Furthermore, the shortage of arable land creates competition between uses for food and fuel, resulting in increased living expenses. This review seeks to summarize recent knowledge in genetics, genomics, and gene expression of a rising model species for bioenergy applications, sorghum. Its diploid genome has been sequenced, it has favorable low-input cost traits, and genetic crosses between different cultivars can be used to study allelic variations of genes involved in stem sugar metabolism and incremental biomass.     

Climate cooling benefits of cellulosic bioenergy crops from elevated albedo

Changes in land surface albedo can alter ecosystem energy balance and potentially influence climate. We examined the albedo of six bioenergy cropping systems in southwest Michigan USA: monocultures of energy sorghum (Sorghum bicolor), switchgrass (Panicum virgatum L.), and giant miscanthus (Miscanthus × giganteus), and polycultures of native grasses, early successional vegetation, and restored prairie. Direct field measurements of surface albedo (α_s) from May 2018 through December 2020 at half-hourly intervals in each system quantified the magnitudes and seasonal differences in albedo (∆_α) and albedo-induced radiative forcing (RF_∆α). We used a nearby forest as a historical native cover type to estimate reference albedo and RF_∆α change upon original land use conversion, and a continuous no-till maize (Zea mays L.) system as a contemporary reference to estimate change upon conversion from annual row crops. Annually, α_s differed significantly (p < 0.05) among crops in the order: early successional (0.288 ± 0.012SE) >> miscanthus (0.271 ± 0.009) ≈ energy sorghum (0.270 ± 0.010) ≥ switchgrass (0.265 ± 0.009) ≈ restored prairie (0.264 ± 0.012) > native grasses (0.259 ± 0.010) > maize (0.247 ± 0.010). Reference forest had the lowest annual α_s (0.134 ± 0.003). Albedo differences among crops during the growing season were also statistically significant, with growing season α_s in perennial crops and energy sorghum on average ~20% higher (0.206 ± 0.003) than in no-till maize (0.184 ± 0.002). Average non-growing season (NGS) α_s (0.370 ± 0.020) was much higher than growing season α_s (0.203 ± 0.003) but these NGS differences were not significant. Overall, the original conversion of reference forest and maize landscapes to perennials provided a cooling effect on the local climate (RF_αMAIZE: −3.83 ± 1.00 W m⁻²; RF_αFOREST: −16.75 ± 3.01 W m⁻²). Significant differences among cropping systems suggest an additional management intervention for maximizing the positive climate benefit of bioenergy crops, with cellulosic crops on average ~9.1% more reflective than no-till maize, which itself was about twice as reflective as the reference forest.     

Genetic manipulation of lignocellulosic biomass for bioenergy

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Changes in soil carbon stocks under perennial and annual bioenergy crops

Bioenergy crops are expected to provide biomass to replace fossil resources and reduce greenhouse gas emissions. In this context, changes in soil organic carbon (SOC) stocks are of primary importance. The aim of this study was to measure changes in SOC stocks in bioenergy cropping systems comparing perennial (Miscanthus × giganteus and switchgrass), semi‐perennial (fescue and alfalfa), and annual (sorghum and triticale) crops, all established after arable crops. The soil was sampled at the start of the experiment and 5 or 6 years later. SOC stocks were calculated at equivalent soil mass, and δ¹³C measurements were used to calculate changes in new and old SOC stocks. Crop residues found in soil at the time of SOC measurements represented 3.5–7.2 t C ha^?1 under perennial crops vs. 0.1–0.6 t C ha^?1 for the other crops. During the 5‐year period, SOC concentrations under perennial crops increased in the surface layer (0–5 cm) and slightly declined in the lower layers. Changes in δ¹³C showed that C inputs were mainly located in the 0–18 cm layer. In contrast, SOC concentrations increased over time under semi‐perennial crops throughout the old ploughed layer (ca. 0–33 cm). SOC stocks in the old ploughed layer increased significantly over time under semi‐perennials with a mean increase of 0.93 ± 0.28 t C ha^?1 yr^?1, whereas no change occurred under perennial or annual crops. New SOC accumulation was higher for semi‐perennial than for perennial crops (1.50 vs. 0.58 t C ha^?1 yr^?1, respectively), indicating that the SOC change was due to a variation in C input rather than a change in mineralization rate. Nitrogen fertilization rate had no significant effect on SOC stocks. This study highlights the interest of comparing SOC changes over time for various cropping systems.     

Long-term variability of root production in bioenergy crops from ingrowth core measurements

用内生长法测定的生物能源作物根生产的长期变化 对于土地用途转为种植生物燃料作物后的根系产量,还很少进行过长期的测定。为了评价此前的土地用途对地下生物量积累的影响,我们在“美国休耕保护项目”(Conservation Reserve Program, CPR)下生长了22年的草地(CRP草地)和使用期超过50年的农业用地(AGR农地)转为种植生物燃料作物玉米(Zea mays, Corn, C)、柳枝稷(Panicum virgatum, Switchgrass, Sw)和恢复性草原植被(Prairie, Pr)。我们将一块CPR草地维持为对照。我们的假设是土地利用历史和作物类型对根系密度有显著的影响;其中,原CRP草地上种植的多年生作物具有较高的根系生产力,而在原农业用地上种植的玉米的根系生产力最低。通过内生长土芯法对内生长根系生物量进行了原位测定,同时对地上净初级生产力(ANPP)进行了测量。包括气温、生长季长度和降水量在内的辅助测量则被用来考查它们对根系生产量的影响。根系生产力在未转变的CRP草地最高(1716 g m⁻² yr⁻¹),而在玉米田中最低(526 g m⁻² yr⁻¹)。由CRP草地和AGR农田转变而来的多年生作物种植地在第一年都具有较低的根系生物量和ANPP,但柳枝稷在2011年达到峰值,恢复后的草原植被也在一年后达到峰值。恢复后的草原生态系统稳定性较高(AGR-Pr: 4.3 ± 0.11; CRP-Pr: 4.1 ± 0.10),而仅种植单一作物的生态系统稳定性都较低。根系生产量与ANPP呈正相关性(R² = 0.40)。总体而言,对生物燃料作物大规模种植过程中的根系生物量积累应予以重视,因为这是固碳的一种主 要来源。     

Genetic improvement of the chemical composition of Scots pine (Pinus sylvestris L.) juvenile wood for bioenergy production

Chemical composition is one of the key characteristics that determines wood quality and in turn its suitability for different end products and applications. The inclusion of chemical compositional traits in forest tree improvement requires high‐throughput techniques capable of rapid, non‐destructive and cost‐efficient assessment of large‐scale breeding experiments. We tested whether Fourier‐transform infrared (FTIR) spectroscopy, coupled with partial least squares regression, could serve as an alternative to traditional wet chemistry protocols for the determination of the chemical composition of juvenile wood in Scots pine for tree improvement purposes. FTIR spectra were acquired for 1,245 trees selected in two Scots pine (Pinus sylvestris L.) full‐sib progeny tests located in northern Sweden. Predictive models were developed using 70 reference samples with known chemical composition (the proportion of lignin, carbohydrates [cellulose, hemicelluloses and their structural monosaccharides glucose, mannose, xylose, galactose, and arabinose] and extractives). Individual‐tree narrow‐sense heritabilities and additive genetic correlations were estimated for all chemical traits as well as for growth (height and stem diameter) and wood quality traits (density and stiffness). Genetic control of the chemical traits was mostly moderate. Of the major chemical components, highest heritabilities were observed for hemicelluloses (0.43–0.47), intermediate for lignin and extractives (0.30–0.39), and lowest for cellulose (0.20–0.25). Additive genetic correlations among chemical traits were, except for extractives, positive while those between chemical and wood quality traits were negative. In both groups (chemical and wood quality traits), correlations with extractives exhibited opposite signs. Correlations of chemical traits with growth traits were near zero. The best strategy for genetic improvement of Scots pine juvenile wood for bioenergy production is to decrease and stabilize the content of extractives among trees and then focus on increasing the cellulose:lignin ratio.     

Candidate perennial bioenergy grasses have a higher albedo than annual row crops

The production of perennial cellulosic feedstocks for bioenergy presents the potential to diversify regional economies and the national energy supply, while also serving as climate ‘regulators’ due to a number of biogeochemical and biogeophysical differences relative to row crops. Numerous observational and model‐based approaches have investigated biogeochemical trade‐offs, such as increased carbon sequestration and increased water use, associated with growing cellulosic feedstocks. A less understood aspect is the biogeophysical changes associated with the difference in albedo (α), which could alter the local energy balance and cause local to regional cooling several times larger than that associated with offsetting carbon. Here, we established paired fields of Miscanthus × giganteus (miscanthus) and Panicum virgatum (switchgrass), two of the leading perennial cellulosic feedstock candidates, and traditional annual row crops in the highly productive ‘Corn‐belt’. Our results show that miscanthus did and switchgrass did not have an overall higher α than current row crops, but a strong seasonal pattern existed. Both perennials had consistently higher growing season α than row crops and winter α did not differ. The lack of observed differences in winter α, however, masked an interaction between snow cover and species differences, with the perennial species, compared with the row crops, having a higher α when snow was absent and a much lower α when snow was present. Overall, these changes resulted in an average net reduction in annual absorbed energy of about 5 W m^?2 for switchgrass and about 8 W m^?2 for miscanthus relative to annual crops. Therefore, the conversion from annual row to perennial crops alters the radiative balance of the surface via changes in α and could lead to regional cooling.     

Consensus,uncertainties and challenges for perennial bioenergy crops and land use

Perennial bioenergy crops have significant potential to reduce greenhouse gas (GHG) emissions and contribute to climate change mitigation by substituting for fossil fuels; yet delivering significant GHG savings will require substantial land‐use change, globally. Over the last decade, research has delivered improved understanding of the environmental benefits and risks of this transition to perennial bioenergy crops, addressing concerns that the impacts of land conversion to perennial bioenergy crops could result in increased rather than decreased GHG emissions. For policymakers to assess the most cost‐effective and sustainable options for deployment and climate change mitigation, synthesis of these studies is needed to support evidence‐based decision making. In 2015, a workshop was convened with researchers, policymakers and industry/business representatives from the UK, EU and internationally. Outcomes from global research on bioenergy land‐use change were compared to identify areas of consensus, key uncertainties, and research priorities. Here, we discuss the strength of evidence for and against six consensus statements summarising the effects of land‐use change to perennial bioenergy crops on the cycling of carbon, nitrogen and water, in the context of the whole life‐cycle of bioenergy production. Our analysis suggests that the direct impacts of dedicated perennial bioenergy crops on soil carbon and nitrous oxide are increasingly well understood and are often consistent with significant life cycle GHG mitigation from bioenergy relative to conventional energy sources. We conclude that the GHG balance of perennial bioenergy crop cultivation will often be favourable, with maximum GHG savings achieved where crops are grown on soils with low carbon stocks and conservative nutrient application, accruing additional environmental benefits such as improved water quality. The analysis reported here demonstrates there is a mature and increasingly comprehensive evidence base on the environmental benefits and risks of bioenergy cultivation which can support the development of a sustainable bioenergy industry.     

Changes in N-transforming archaea and bacteria in soil during the establishment of bioenergy crops

Widespread adaptation of biomass production for bioenergy may influence important biogeochemical functions in the landscape, which are mainly carried out by soil microbes. Here we explore the impact of four potential bioenergy feedstock crops (maize, switchgrass, Miscanthus X giganteus, and mixed tallgrass prairie) on nitrogen cycling microorganisms in the soil by monitoring the changes in the quantity (real-time PCR) and diversity (barcoded pyrosequencing) of key functional genes (nifH, bacterial/archaeal amoA and nosZ) and 16S rRNA genes over two years after bioenergy crop establishment. The quantities of these N-cycling genes were relatively stable in all four crops, except maize (the only fertilized crop), in which the population size of AOB doubled in less than 3 months. The nitrification rate was significantly correlated with the quantity of ammonia-oxidizing archaea (AOA) not bacteria (AOB), indicating that archaea were the major ammonia oxidizers. Deep sequencing revealed high diversity of nifH, archaeal amoA, bacterial amoA, nosZ and 16S rRNA genes, with 229, 309, 330, 331 and 8989 OTUs observed, respectively. Rarefaction analysis revealed the diversity of archaeal amoA in maize markedly decreased in the second year. Ordination analysis of T-RFLP and pyrosequencing results showed that the N-transforming microbial community structures in the soil under these crops gradually differentiated. Thus far, our two-year study has shown that specific N-transforming microbial communities develop in the soil in response to planting different bioenergy crops, and each functional group responded in a different way. Our results also suggest that cultivation of maize with N-fertilization increases the abundance of AOB and denitrifiers, reduces the diversity of AOA, and results in significant changes in the structure of denitrification community.     

农村废弃生物质资源开发获重要突破

能源危机是当今世界面临的严峻挑战之一[1].化石能源是地球亿万年间积累起来的光合产物,是不可再生的资源.大量化石能源开挖后,沉睡了数亿年的"碳库"最终又要变成"碳源",这使人类本来任务艰巨的碳减排 "雪上加霜"[2,3].为逃脱化石能源怪圈,全球能源与环境科学家们,把精力转移到用太阳能、风能、生物质能等清洁能源代替化石能源上来,取得了重要进展.但新能源开发仍存在着成本高,经济效益差的不足[4～6].作为全球最大的发展中国家,中国科学家正努力寻找能高效利用农村生物质资源的新方法.研究成果一旦获得推广,可大大缓解能源紧缺状况,对全球碳减排意义重大 [7,8].     

An integrated biogeochemical and economic analysis of bioenergy crops in the Midwestern United States

This study integrates a biophysical model with a county‐specific economic analysis of breakeven prices of bioenergy crop production to assess the biophysical and economic potential of biofuel production in the Midwestern United States. The bioenergy crops considered in this study include a genotype of Miscanthus, Miscanthus×giganteus, and the Cave‐in‐Rock breed of switchgrass (Panicum virgatum). The estimated average peak biomass yield for miscanthus in the Midwestern states ranges between 7 and 48 metric tons dry matter per hectare per year ( t DM ha^?1 yr^?1), while that for switchgrass is between 10 and 16 t DM ha^?1 yr^?1. With the exception of Minnesota and Wisconsin, where miscanthus yields are likely to be low due to cold soil temperatures, the yield of miscanthus is on average more than two times higher than yield of switchgrass. We find that the breakeven price, which includes the cost of producing the crop and the opportunity cost of land, of producing miscanthus ranges from $53 t^?1 DM in Missouri to $153 t^?1 DM in Minnesota in the low‐cost scenario. Corresponding costs for switchgrass are $88 t^?1 DM in Missouri to $144 t^?1 DM in Minnesota. In the high‐cost scenario, the lowest cost for miscanthus is $85 t^?1 DM and for switchgrass is $118 t^?1 DM, both in Missouri. These two scenarios differ in their assumptions about ease of establishing the perennial crops, nutrient requirements and harvesting costs and losses. The differences in the breakeven prices across states and across crops are mainly driven by bioenergy and row crop yields per hectare. Our results suggest that while high yields per unit of land of bioenergy crops are critical for the competitiveness of bioenergy feedstocks, the yields of the row crops they seek to displace are also an important consideration. Even high yielding crops, such as miscanthus, are likely to be economically attractive only in some locations in the Midwest given the high yields of corn and soybean in the region.     

Food and bioenergy: reviewing the potential of dual‐purpose wheat crops

Within the bioenergy debate, the ‘food vs. fuel’ controversy quickly replaced enthusiasm for biofuels derived from first‐generation feedstocks. Second‐generation biofuels offer an opportunity to produce fuels from dedicated energy crops, waste materials or coproducts such as cereal straw. Wheat represents one of the most widely grown arable crops around the world, with wheat straw, a potential source of biofuel feedstock. Wheat straw currently has limited economic value; hence, wheat cultivars have been bred for increased grain yield; however, with the development of second‐generation biofuel production, utilization of straw biomass provides the potential for ‘food and fuel’. Reviewing the evidence for the development of dual‐purpose wheat cultivars optimized for food grain and straw biomass production, we present a holistic assessment of a potential ideotype for a dual‐purpose cultivar (DPC). An ideal DPC would be characterized by high grain and straw yields, high straw digestibility (i.e. biofuel yield potential) and good lodging resistance. Considerable variation in these traits exists among current wheat cultivars, facilitating the selection of improved individual traits; however, increasing straw yield and digestibility could potentially have negative trade‐off impacts on grain yield and lodging resistance, reducing the feasibility of a single ideotype. Adoption of alternative management practices could potentially increase straw yield and digestibility, albeit these practices are also associated with potential trade‐offs among cultivar traits. Benefits from using DPCs include reduced logistics costs along the biofuel feedstock supply chain, but practical barriers to differential pricing for straw digestibility traits are likely to reduce the financial incentive to farmers for growing higher ‘biofuel‐quality’ straw cultivars. Further research is required to explore the relationships among the ideotype traits to quantify potential DPC benefits; this will help to determine whether stakeholders along the bioenergy feedstock supply chain will invest in the development of DPCs that provide food and fuel potential.     

Integrated genomic selection for rapid improvement of crops

An increase in the rate of crop improvement is essential for achieving sustained food production and other needs of ever-increasing population. Genomic selection (GS) is a potential breeding tool that has been successfully employed in animal breeding and is being incorporated into plant breeding. GS promises accelerated breeding cycles through a rapid selection of superior genotypes. Numerous empirical and simulation studies on GS and realized impacts on improvement in the crop yields are recently being reported. For a holistic understanding of the technology, we briefly discuss the concept of genetic gain, GS methodology, its current status, advantages of GS over other breeding methods, prediction models, and the factors controlling prediction accuracy in GS. Also, integration of speed breeding and other novel technologies viz. high throughput genotyping and phenotyping technologies for enhancing the efficiency and pace of GS, followed by its prospective applications in varietal development programs is reviewed.     

Genetic improvement of pyrethrum

Summary Pyrethrum (Chrysanthemum cinerariefolium), an important paramedicinal plant is a potential source of pyrethrins, which have a long history of safe uses against mosquito larvae — a carrier of malarial parasite. It was introduced in India from Kenya in 1931. Considerable genetic diversity has been generated over the years. Repeated clonal selection could lead to isolation of a number of divergent clones representing selective divergence. Planned hybridization among some of the chosen clones could further enlarge the spectrum of variation as measured by multivariate analyses (D²-statistic and canonical analysis). The resulting hybrids manifested a variable degree of heterosis which was found to be, by and large, positively associated with the degree of divergence between the two constituent parents of a hybrid. However, the choice of the potential hybrid clone(s) for commercial exploitation was most viable when parents for hybridization were short-listed on the basis of parental divergence coupled essentially with per se performance for specific traits. The latter criterion assumes greater significance since low x low or medium x low parental hybrids also tended to register high heterosis for both the pyrethrins content and yield. Four hybrids: 234xL, 8xL, 326×395 and 319xL were identified to be the most promising for clonal selection.CIMAP publication no. 9189