Dedicated Bioenergy Crops Research Articles

A regional assessment of land‐based carbon mitigation potentials: Bioenergy, BECCS, reforestation, and forest management

AbstractLand‐based solutions are indispensable features of most climate mitigation scenarios. Here we conduct a novel cross‐sectoral assessment of regional carbon mitigation potential by running an ecosystem model with an explicit representation of forest structure and climate impacts for Bavaria, Germany, as a case study. We drive the model with four high‐resolution climate projections (EURO‐CORDEX) for the representative concentration pathway RCP4.5 and present‐day land‐cover from three satellite‐derived datasets (CORINE, ESA‐CCI, MODIS) and identify total mitigation potential by not only accounting for carbon storage but also material and energy substitution effects. The model represents the current state in Bavaria adequately, with a simulated forest biomass 12.9 ± 0.4% lower than data from national forest inventories. Future land‐use changes according to two ambitious land‐use harmonization scenarios (SSP1xRCP2.6, SSP4xRCP3.4) achieve a mitigation of 206 and 247 Mt C (2015–2100 period) via reforestation and the cultivation and burning of dedicated bioenergy crops, partly combined with carbon capture and storage. Sensitivity simulations suggest that converting croplands or pastures to bioenergy plantations could deliver a carbon mitigation of 40.9 and 37.7 kg C/m2, respectively, by the year 2100 if used to replace carbon‐intensive energy systems and combined with CCS. However, under less optimistic assumptions (including no CCS), only 15.3 and 12.2 kg C/m2 are mitigated and reforestation might be the better option (20.0 and 16.8 kg C/m2). Mitigation potential in existing forests is limited (converting coniferous into mixed forests, nitrogen fertilization) or even negative (suspending wood harvest) due to decreased carbon storage in product pools and associated substitution effects. Our simulations provide guidelines to policy makers, farmers, foresters, and private forest owners for sustainable and climate‐benefitting ecosystem management in temperate regions. They also emphasize the importance of the CCS technology which is regarded critically by many people, making its implementation in the short or medium term currently doubtable.

Engineering of Bioenergy Crops: Dominant Genetic Approaches to Improve Polysaccharide Properties and Composition in Biomass

Large-scale, sustainable production of lignocellulosic bioenergy from biomass will depend on a variety of dedicated bioenergy crops. Despite their great genetic diversity, prospective bioenergy crops share many similarities in the polysaccharide composition of their cell walls, and the changes needed to optimize them for conversion are largely universal. Therefore, biomass modification strategies that do not depend on genetic background or require mutant varieties are extremely valuable. Due to their preferential fermentation and conversion by microorganisms downstream, the ideal bioenergy crop should contain a high proportion of C6-sugars in polysaccharides like cellulose, callose, galactan, and mixed-linkage glucans. In addition, the biomass should be reduced in inhibitors of fermentation like pentoses and acetate. Finally, the overall complexity of the plant cell wall should be modified to reduce its recalcitrance to enzymatic deconstruction in ways that do no compromise plant health or come at a yield penalty. This review will focus on progress in the use of a variety of genetically dominant strategies to reach these ideals. Due to the breadth and volume of research in the field of lignin bioengineering, this review will instead focus on approaches to improve polysaccharide component plant biomass. Carbohydrate content can be dramatically increased by transgenic overexpression of enzymes involved in cell wall polysaccharide biosynthesis. Additionally, the recalcitrance of the cell wall can be reduced via the overexpression of native or non-native carbohydrate active enzymes like glycosyl hydrolases or carbohydrate esterases. Some research in this area has focused on engineering plants that accumulate cell wall-degrading enzymes that are sequestered to organelles or only active at very high temperatures. The rationale being that, in order to avoid potential negative effects of cell wall modification during plant growth, the enzymes could be activated post-harvest, and post-maturation of the cell wall. A potentially significant limitation of this approach is that at harvest, the cell wall is heavily lignified, making the substrates for these enzymes inaccessible and their activity ineffective. Therefore, this review will only include research employing enzymes that are at least partially active under the ambient conditions of plant growth and cell wall development.

Soil carbon increased by twice the amount of biochar carbon applied after 6 years: Field evidence of negative priming

AbstractApplying biochar to agricultural soils has been proposed as a means of sequestering carbon (C) while simultaneously enhancing soil health and agricultural sustainability. However, our understanding of the long‐term effects of biochar and annual versus perennial cropping systems and their interactions on soil properties under field conditions is limited. We quantified changes in soil C concentration and stocks, and other soil properties 6 years after biochar applications to corn (Zea mays L.) and dedicated bioenergy crops on a Midwestern US soil. Treatments were as follows: no‐till continuous corn, Liberty switchgrass (Panicum virgatum L.), and low‐diversity prairie grasses, 45% big bluestem (Andropogon gerardii), 45% Indiangrass (Sorghastrum nutans), and 10% sideoats grama (Bouteloua curtipendula), as main plots, and wood biochar (9.3 Mg/ha with 63% total C) and no biochar applications as subplots. Biochar‐amended plots accumulated more C (14.07 Mg soil C/ha vs. 2.25 Mg soil C/ha) than non‐biochar‐amended plots in the 0–30 cm soil depth but other soil properties were not significantly affected by the biochar amendments. The total increase in C stocks in the biochar‐amended plots was nearly twice (14.07 Mg soil C/ha) the amount of C added with biochar 6 years earlier (7.25 Mg biochar C/ha), suggesting a negative priming effect of biochar on formation and/or mineralization of native soil organic C. Dedicated bioenergy crops increased soil C concentration by 79% and improved both aggregation and plant available water in the 0–5 cm soil depth. Biochar did not interact with the cropping systems. Overall, biochar has the potential to increase soil C stocks both directly and through negative priming, but, in this study, it had limited effects on other soil properties after 6 years.

Biomass yield, chemical composition and theoretical ethanol yield for different genotypes of energy sorghum cultivated on marginal land in China

Energy sorghum [Sorghum bicolor (L). Moench] is potentially of great significance for bioethanol production because of its high biomass and wide adaptability. In this study, a field experiment was conducted on a semiarid marginal land in Inner Mongolia (39°10′N, 109°53′E), China, to assess the effects of genotypes with similar growth duration and biomass yield levels on chemical composition and theoretical ethanol yield (TEY) in both leaves and stems of four genotypes each of sweet and biomass sorghum in 2013 and 2014. Among all varieties, no significant variation was observed in the biomass yield of leaf (1.81–2.55 Mg ha−1) and stem (3.73–4.87 Mg ha−1), which was relatively low due to the marginal land with low temperature conditions. By contrast, considerable variation was detected in soluble sugars, ash and hexose contents of leaves and stems among the sweet sorghum varieties over two years. Compared with the sweet type, biomass sorghum varieties exhibited significantly lower soluble sugars content but higher cellulose, hemicellulose, and lignin contents in both leaf and stem tissues, resulting in significantly lower hexose and higher pentose contents. Moreover, stems exhibited significantly higher total content of hexose and pentose (725.4 g kg−1) than leaves (642.3 g kg−1) across all varieties, leading to significantly higher TEY of stems than that of leaves. Despite the slightly higher TEY of sweet sorghum, biomass sorghum varieties exhibited particularly stable chemical components and TEY across both experimental years, resulting in greater potential for industrial bioethanol production in this study. Overall, varietal selection was effective in improving the biomass feedstock quality of energy sorghum for biochemical conversion. The findings of this study will help to facilitate industrial bioethanol production from dedicated bioenergy crops.

Joint linkage and association mapping of complex traits in shrub willow (Salix purpurea L.).

Increasing energy demands and the necessity to reduce greenhouse gas emissions are key motivating factors driving the development of lignocellulosic crops as an alternative to non-renewable energy sources. The effects of global climate change will require a better understanding of the genetic basis of complex adaptive traits to breed more resilient bioenergy feedstocks, like willow (Salix spp.). Shrub willow is a sustainable and dedicated bioenergy crop, bred to be fast-growing and high-yielding on marginal land without competing with food crops. In a rapidly changing climate, genomic advances will be vital for the sustained improvement of willow and other non-model bioenergy crops. Here, joint genetic mapping was used to exploit genetic variation garnered from both recent and historical recombination events in S. purpurea. A panel of North American naturalized S. purpurea accessions and full-sib F2S. purpurea population were genotyped and phenotyped for a suite of morphological, physiological, pest and disease resistance, and wood chemical composition traits, collected from multi-environment and multi-year replicated field trials. Controlling for population stratification and kinship in the association panel and spatial variation in the F2, a comprehensive mixed model analysis was used to dissect the complex genetic architecture and plasticity of these important traits. Individually, genome-wide association (GWAS) models differed in terms of power, but the combined approach, which corrects for yearly and environmental co-factors across datasets, improved the overall detection and resolution of associated loci. Although there were few significant GWAS hits located within support intervals of QTL for corresponding traits in the F2, many large-effect QTL were identified, as well as QTL hotspots. This study provides the first comparison of linkage analysis and linkage disequilibrium mapping approaches in Salix, and highlights the complementarity and limits of these two methods for elucidating the genetic architecture of complex bioenergy-related traits of a woody perennial breeding programme.

Symbolic meanings, landowner support, and dedicated bioenergy crops in the rural northeastern United States

Recent research on social acceptance of large-scale renewable energy systems development has turned from an earlier focus on social opposition, such as Not In My Backyard (NIMBY) stances, toward assessing the ‘symbolic fit’ between meanings for place and proposed technology development that people near development sites hold. This quantitative study extends the symbolic fit hypothesis by testing how varied combinations of meanings for place and technology influence Northeast U.S. rural landowners’ support for dedicated bioenergy crop production in their communities. Drawing on a survey of 907 landowners who have ten or more acres of land suitable for perennial bioenergy crops, we tested ten combinations of symbolic meanings regarding bioenergy crop technologies and land as place. We found that when combined with either protectionist or utilitarian meanings for one’s land, viewing bioenergy crop production as an innovative way to address environmental challenges increased the likelihood of support for local development of bioenergy crops. Similarly, different symbolic meanings regarding one’s land combined with seeing little community benefit from bioenergy crops reduced the likelihood of support. Given the important role of private landowners in many regions of Western nations considering bioenergy development, the symbolic meanings held by landowners merit attention. By recognizing the complex, conjunctural sources of meanings that inform landowners’ propensities to support new renewable energy project development, new and emerging energy projects can incorporate more polyvalent views into design and implementation and approach public engagement opportunities accordingly.

Fungal Community Structural and Microbial Functional Pattern Changes After Soil Amendments by Oilseed Meals of Jatropha curcas and Camelina sativa: A Microcosm Study.

The meals after oil extraction from many oilseed crops have nutrition and biofumigation potential for land application. Oilseed meal (SM) from the dedicated bioenergy crop Jatropha curcas were implicated to contain compounds that have antibacterial properties on some soil pathogens. However, little is known about its effect on non-targeted soil microbial community, especially on fungi. SM from Camelina sativa contains moderate level of glucosinolates (GLS) and was under studied. To investigate soil fungal community responses to jatropha and camelina SMs, we conducted a lab based microcosm study, amending soil with 1% SMs of jatropha, camelina, flax, and biomass of wheat straw. Fungal community abundance and structure were analyzed based on the ITS region using qPCR and tag-pyrosequencing. Microbial functional changes were examined by community level physiological profile (CLPP) using Biolog assay. Both SMs from jatropha and camelina showed biofumigant properties and inhibited fungal proliferation. Jatropha SM significantly altered soil fungal community structures with lower fungal biodiversity and higher Chaetomium composition. Camelina SM amended soil promoted Fusarium proliferation. CLPP indicated sequential hierarchy for C metabolism in the oilseed-amended microcosms was generally complex C > phosphate-associated C > carboxylic acids > carbohydrates > amines > amino acids. No significant difference in CLPP was detected due to the type of SM treatment. Our data indicate that both SMs of jatropha and camelina have biofumigant properties and can differentially impact soil microbial communities, and the changes were relatively persistent over time. Microbial functional patterns on the other side were not impacted by SM type. Our study revealed biofumigant and nutritional influence of SMs from dedicated biofuel plants on soil microbial community. This information will help properly using jatropha and camelina SMs for pathogen control while minimizing their negative impacts on non-target microorganisms. However, further studies in the field are demanded to investigate their influences in real practice.

Dedicated Bioenergy Crops and Water Erosion.

Information on the water quality impact of perennial warm-season grasses (WSGs) when grown in marginal lands as dedicated energy crops is limited. We studied how WSGs affected runoff, sediment, and nutrient losses and related near-surface soil properties to those of no-till corn ( L.) on an eroded soil in southwestern Iowa and a center pivot corner in east-central Nebraska. The experiment at the eroded soil was established in 2012, and treatments included 'Liberty' switchgrass ( L.) and no-till continuous corn. The experiment at the pivot corner was established in 2013 with 'Liberty' switchgrass, 'Shawnee' switchgrass, low-diversity grass mixture, and corn. We simulated rainfall at 63.5 ± 2.8 mm h for 1 h to portray 5-yr return periods and measured water erosion in spring 2017. Time to runoff start and runoff depth did not differ between WSGs and corn. On the eroded soil, sediment and nutrient losses did not differ between treatments. At the pivot corner, sediment (0.71 vs. 0.15 Mg ha) and PO-P (0.037 vs. 0.006 kg ha) losses were five times higher in corn than in WSGs. Near-surface soil properties did not differ on the eroded soil, but at the pivot corner, wet aggregate stability was four times higher and residue cover was 34% higher in WSGs than in corn. Water-stable aggregates were negatively correlated with NO-N and PO-P losses. Overall, WSGs can improve water quality in marginally productive croplands, but their effectiveness appears to be site specific.

Contribution of sugarcane crop wild relatives in the creation of improved varieties in Mauritius

AbstractSignificant genetic diversity for sucrose and fibre percentages exists in the species that served as the foundation of present day sugarcane cultivars. However, information is lacking worldwide on the recent contributions of sugarcane crop wild relatives (mainly Saccharum, Erianthus and Miscanthus wild species) in developing new varieties. There is renewed interest in using those relatives for creating new varieties to use as a dedicated bioenergy crop with higher fibre. This study focuses on past data analysis of sugarcane breeding in Mauritius with the objective to assess the efficiency in exploiting sugarcane wild relatives since 1970s to date. Pedigree analyses helped retrace the parentages of elite inter-specific hybrids reaching the final stages of selection. The studies confirmed the high prevalence of a few ‘wonder canes’ (successful hybrids with wild canes produced in the beginning of last century) among the ancestors of Mauritian varieties. Among the wild relatives, eight Saccharum spontaneum, two S. robustum, and one Erianthus clones were involved in generating elite genotypes worth evaluating at the advanced variety trial stages. A few early generation hybrids were released in the past for industrial exploitation, the latest one being M 1002/02 in 2016, with sugar as the primary output. Recent studies on the biomass potential and fibre yield of inter-specific hybrids are giving promising results, which expands the horizon in the use of sugarcane wild relatives for the generation of novel type of sugarcane varieties for multiple end-uses.

Stem, Leaf, and Panicle Yield and Nutrient Content of Biomass and Sweet Sorghum

Core Ideas Sorghum is a potential dedicated bioenergy crop both from biomass and sugar yields. Increasing rates of N fertilizer affected biomass yield and nutrient removal for sorghum cultivar ES5200 by partitioning resources primarily toward the stem component. For sorghum M81‐E, the seed head component accounted for a greater proportion of biomass, compared with sorghum ES5200, and biomass yield and nutrients were more evenly distributed among the three components. Returning the leaf and seed head components back to the field to enhance soil fertility has the potential to provide at least 45, 7, and, 26 kg ha−1 of N, P, and K, respectively. Information on biomass yield and nutrient content among leaf, stem, and head components can aid on sorghum [Sorghum bicolor (L.) Moench] cultivar selection and harvest management practices to optimize the quality of the harvested feedstock and residue management. The objectives of this study were to characterize and to determine the effect of five N fertilization rates (0, 67, 134, 201, and 268 kg ha−1) on biomass yield and N, P, and K content of the stem, leaf, and panicle components of two dedicated bioenergy sorghum cultivars. Biomass sorghum Blade ES5200 and sweet sorghum M81‐E were grown in 2014 and 2015 in North Carolina. For ES5200, total biomass yield was 14.4 Mg ha−1 with 74, 25, and 2% accounted by the stem, leaf, and panicle, respectively. For M81‐E, total biomass yield was 11.5 Mg ha−1 with 62, 24, and 15% accounted by the stem, leaf, and panicle, respectively. Nutrient content by the leaf + panicle components combined were about 45, 7, and 26 kg ha−1 for N, P, and K, respectively, for both cultivars; however, for ES5200, the leaf + panicle components combined accounted for 46, 37, and 16% of total N, P, and K content, respectively, whereas for M81‐E they accounted for 62, 74, and 24% of total N, P, and K content, respectively. Addition of N fertilizer resulted in greater shifts in the stem component responses but to different extents for each cultivar.

Susceptibility and yield response to sugarcane borer (Lepidoptera: Crambidae) infestation among sugarcanes and sorghums with potential for bioethanol production

The U.S. Gulf Coast has ideal conditions, including abundant rainfall and a long growing season, for production of dedicated bioenergy crops. Interest in producing bioethanol from high-biomass graminaceous crops including energycanes (Saccharum spp.) and energy sorghums (Sorghum spp. hybrids) in the region has increased. However, insect pests including the sugarcane borer, Diatraea saccharalis (F.) (Lepidoptera: Crambidae), will likely adversely affect bioenergy crops. The impact of D. saccharalis infestations on yields of conventional and bioenergy sugarcanes and sorghums was investigated in three separate field studies conducted from 2012 to 2013. These studies compared D. saccharalis injury and crop yield parameters among insecticide-protected and unprotected plots of sugarcanes, energycanes, high biomass sorghums, and sweet sorghum. In unprotected plots, D. saccharalis injury ranged from 2.9 (resistant sugarcane) to 13.6% bored internodes (susceptible sugarcane). A resistant energycane cultivar was among the least injured (3.5% bored internodes) and demonstrated the greatest potential for bioethanol production with an average of >17,000 L/ha. Linear regressions revealed negative relationships between percentage of bored internodes and ethanol yield in all cultivars. At one location, D. saccharalis injury resulted in a 13% reduction in bioethanol production across all years and cultivars. These studies indicate D. saccharalis has potential to substantially reduce yields in bioenergy crops and pest management programs will be needed to maximize ethanol production.

Functional Diversity of Diterpene Synthases in the Biofuel Crop Switchgrass.

Diterpenoids constitute a diverse class of metabolites with critical functions in plant development, defense, and ecological adaptation. Major monocot crops, such as maize (Zea mays) and rice (Oryza sativa), deploy diverse blends of specialized diterpenoids as core components of biotic and abiotic stress resilience. Here, we describe the genome-wide identification and functional characterization of stress-related diterpene synthases (diTPSs) in the dedicated bioenergy crop switchgrass (Panicum virgatum). Mining of the allotetraploid switchgrass genome identified an expansive diTPS family of 31 members, and biochemical analysis of 11 diTPSs revealed a modular metabolic network producing a diverse array of diterpenoid metabolites. In addition to ent-copalyl diphosphate (CPP) and ent-kaurene synthases predictably involved in gibberellin biosynthesis, we identified syn-CPP and ent-labda-13-en-8-ol diphosphate (LPP) synthases as well as two diTPSs forming (+)-labda-8,13E-dienyl diphosphate (8,13-CPP) and ent-neo-cis-trans-clerodienyl diphosphate (CT-CLPP) scaffolds not observed previously in plants. Structure-guided mutagenesis of the (+)-8,13-CPP and ent-neo-CT-CLPP synthases revealed residue substitutions in the active sites that altered product outcome, representing potential neofunctionalization events that occurred during diversification of the switchgrass diTPS family. The conversion of ent-CPP, ent-LPP, syn-CPP, and ent-neo-CT-CLPP by promiscuous diTPSs further yielded distinct labdane-type diterpene olefins and alcohols. Of these metabolites, the formation of 9β-hydroxy-syn-pimar-15-ene and the expression of the corresponding genes were induced in roots and leaves in response to oxidative stress and ultraviolet irradiation, indicating their possible roles in abiotic stress adaptation. Together, these findings expand the known chemical space of diterpenoid metabolism in monocot crops toward systematically investigating and ultimately improving stress resilience traits in crop species.

Overexpression of gene encoding the key enzyme involved in proline-biosynthesis (PuP5CS) to improve salt tolerance in switchgrass (Panicum virgatum L.).

Genetic improvement through overexpressing PuP5CS in switchgrass is feasible for enhancing plant salt stress tolerance. Switchgrass (Panicum virgatum L.) has developed into a dedicated bioenergy crop. To improve the biomass production of switchgrass grown on different types of soil, abiotic stress tolerance traits are considered for its genetic improvement. Proline accumulation is a widespread response when plants are subjected to abiotic stresses such as drought, cold and salinity. In plants, P5CS gene encodes the key regulatory enzyme that plays a crucial role in proline biosynthesis. Here, we introduced the PuP5CS gene (from Puccinellia chinampoensis) into switchgrass by Agrobacterium-mediated transformation. Transgenic lines overexpressing the PuP5CS gene showed phenotypic advantages, in leaf width, internode diameter, internode length, tiller numbers and precocious flowering under normal conditions, and the transgenic lines displayed better regenerative capacity in forming more tillers after harvest. Moreover, the PuP5CS gene enhanced the salt tolerance of transgenic switchgrass by altering a wide range of physiological responses. In accordance with the physiological results, histological analysis of cross sections through the leaf blade showed that the areas of bulliform cells and bundle sheath cells were significantly increased in PuP5CS-overexpressing leaves. The expression levels of ROS scavenging-associated genes in transgenic plants were higher than in control plants under salt stress. The results show that genetic improvement through overexpressing PuP5CS in switchgrass is feasible for enhancing plant stress tolerance.

Lignocellulosic‐based bioenergy and water quality parameters: a review

AbstractHigh rates of crop residue removal as biofuel feedstocks could increase losses of nonpoint source pollutants, negatively affecting water quality. An alternative to residue removal can be growing dedicated bioenergy crops such as warm season grasses (WSGs) and short‐rotation woody crops (SRWCs). Yet, our understanding of the implications of growing dedicated bioenergy crops on water quality is limited. Thus, we (i) synthesized and compared the impacts of crop residue removal, WSGs, and SRWCs on water quality parameters (i.e., sediment and nutrient runoff, and nutrient leaching) and (ii) identified research gaps for growing dedicated energy crops. Literature indicates that residue removal at rates >50% (residue retention up to 4.71 Mg ha−1) can increase runoff by 5–15 mm, sediment loss by 0.2–7 Mg ha−1, NO3–N by 0.58–1 kg ha−1, and sediment‐associated C by 0.3–57 kg ha−1 per rainstorm event compared to no residue removal. Crop residue removal may also increase nutrient leaching. Studies on the impacts of growing WSGs as dedicated bioenergy crops at field scale on water quality parameters are few. However, WSGs when used as conservation buffers reduce losses of sediment by 66–97%, nutrients by 21–94%, and contaminants by 9–98%. This suggests that if WSGs were grown as dedicated bioenergy crops at larger scales, they could reduce losses of nonpoint source pollutants. Literature indicates that SRWCs can consistently reduce NO3–N leaching. More modeled than field data are available, warranting further field research on (i) field data collection from WSGs and SRWCs from marginal lands, (ii) growing monoculture or polyculture of WSGs, and (iii) large‐scale production of energy crops. Overall, dedicated bioenergy crops, particularly WSGs, can reduce losses of nonpoint source pollutants compared to residue removal and be an important strategy to improve water quality if grown at larger scales.

Differential growth response to fertilization of ten elite shrub willow (Salix spp.) bioenergy cultivars

Shrub willow triploid hybrid cultivars obtained the greatest aboveground biomass compared to diploid and tetraploid cultivars, and greater biomass was highly correlated with leaf traits and rapid early stem elongation. Shrub willow (Salix L. spp.) is a strong candidate for use as a dedicated bioenergy crop in moist, temperate climates due to high growth rates, excellent regenerative properties and relatively low nutrient demand. Large discrepancies exist in the literature as to the benefits of fertilization for improving biomass production. Controlled environment fertilization studies can remove some confounding edaphic and climatic factors present in field studies. Ten top-performing commercial or pre-commercial cultivars, mostly bred in the US, were assessed for response to five fertilization levels by measuring 20 biomass and growth traits. Triploid hybrid Salix viminalis × S. miyabeana cultivars had the greatest total aboveground biomass, as well as high stem biomass. There was a strong relationship between early stem growth and final aboveground biomass, but only under adequate fertilization. Different strategies for high biomass production among cultivars are discussed in the context of nitrogen investment in leaves. Comparing field trial results and this greenhouse experiment indicates that while the yield ranking is generally preserved, the greenhouse results diverged greatly for two cultivars.

Evaluating the use of biomass energy with carbon capture and storage in low emission scenarios

Biomass Energy with Carbon Capture and Storage (BECCS) is heavily relied upon in scenarios of future emissions that are consistent with limiting global mean temperature increase to 1.5 °C or 2 °C above pre-industrial. These temperature limits are defined in the Paris Agreement in order to reduce the risks and impacts of climate change. Here, we explore the use of BECCS technologies in a reference scenario and three low emission scenarios generated by an integrated assessment model (IMAGE). Using these scenarios we investigate the feasibility of key implicit and explicit assumptions about these BECCS technologies, including biomass resource, land use, CO2 storage capacity and carbon capture and storage (CCS) deployment rate. In these scenarios, we find that half of all global CO2 storage required by 2100 occurs in USA, Western Europe, China and India, which is compatible with current estimates of regional CO2 storage capacity. CCS deployment rates in the scenarios are very challenging compared to historical rates of fossil, renewable or nuclear technologies and are entirely dependent on stringent policy action to incentivise CCS. In the scenarios, half of the biomass resource is derived from agricultural and forestry residues and half from dedicated bioenergy crops grown on abandoned agricultural land and expansion into grasslands (i.e. land for forests and food production is protected). Poor governance of the sustainability of bioenergy crop production can significantly limit the amount of CO2 removed by BECCS, through soil carbon loss from direct and indirect land use change. Only one-third of the bioenergy crops are grown in regions associated with more developed governance frameworks. Overall, the scenarios in IMAGE are ambitious but consistent with current relevant literature with respect to assumed biomass resource, land use and CO2 storage capacity.

Shrub Willow Biomass Production Ranking Across Three Harvests in New York and Minnesota

Shrub willow has potential for being a viable dedicated bioenergy crop in temperate northern latitudes of the USA. Selection of high-producing willow cultivars is critical for economic viability and long-term sustainability of willow production systems. Long-term trials are needed in different geographic areas to better understand genetic by environment interactions on biomass yield for greater profitability and to enhance future breeding efforts. Field trials were conducted in two contrasting environments, northern New York and southern Minnesota, to explore changes in shrub willow yield ranking over three harvest cycles across a range of cultivars and diversity groups. Overall, the MN site produced higher, more stable biomass yields than the NY site due primarily to more productive soils, warmer climate, and less weed pressure. However, between-site differences in willow biomass yield were nominal after the second harvest cycle. Yield variability among the top five willow cultivars at each harvest was significantly less than variability among all cultivars regardless of site. Shrub willow cultivars identified in the top-ranking groups were different between sites. Results show that willow can be a viable long-term crop for sustained biomass feedstock production across a wide range of soils and climates but proper cultivar selection is critical for biological and economic success.

The TcEG1 beetle (Tribolium castaneum) cellulase produced in transgenic switchgrass is active at alkaline pH and auto-hydrolyzes biomass for increased cellobiose release

BackgroundGenetically engineered biofuel crops, such as switchgrass (Panicum virgatum L.), that produce their own cell wall-digesting cellulase enzymes would reduce costs of cellulosic biofuel production. To date, non-bioenergy plant models have been used in nearly all studies assessing the synthesis and activity of plant-produced fungal and bacterial cellulases. One potential source for cellulolytic enzyme genes is herbivorous insects adapted to digest plant cell walls. Here we examine the potential of transgenic switchgrass-produced TcEG1 cellulase from Tribolium castaneum (red flour beetle). This enzyme, when overproduced in Escherichia coli and Saccharomyces cerevisiae, efficiently digests cellulose at optima of 50 °C and pH 12.0.ResultsTcEG1 that was produced in green transgenic switchgrass tissue had a range of endoglucanase activity of 0.16–0.05 units (µM glucose release/min/mg) at 50 °C and pH 12.0. TcEG1 activity from air-dried leaves was unchanged from that from green tissue, but when tissue was dried in a desiccant oven (46 °C), specific enzyme activity decreased by 60%. When transgenic biomass was “dropped-in” into an alkaline buffer (pH 12.0) and allowed to incubate at 50 °C, cellobiose release was increased up to 77% over non-transgenic biomass. Saccharification was increased in one transgenic event by 28%, which had a concurrent decrease in lignin content of 9%. Histological analysis revealed an increase in cell wall thickness with no change to cell area or perimeter. Transgenic plants produced more, albeit narrower, tillers with equivalent dry biomass as the control.ConclusionsThis work describes the first study in which an insect cellulase has been produced in transgenic plants; in this case, the dedicated bioenergy crop switchgrass. Switchgrass overexpressing the TcEG1 gene appeared to be morphologically similar to its non-transgenic control and produced equivalent dry biomass. Therefore, we propose TcEG1 transgenics could be bred with other transgenic germplasm (e.g., low-lignin lines) to yield new switchgrass with synergistically reduced recalcitrance to biofuel production. In addition, transgenes for other cell wall degrading enzymes may be stacked with TcEG1 in switchgrass to yield complementary cell wall digestion features and complete auto-hydrolysis.

The miR156-SPL4 module predominantly regulates aerial axillary bud formation and controls shoot architecture.

Grasses possess basal and aerial axillary buds. Previous studies have largely focused on basal bud (tiller) formation but scarcely touched on aerial buds, which may lead to aerial branch development. Genotypes with and without aerial buds were identified in switchgrass (Panicum virgatum), a dedicated bioenergy crop. Bud development was characterized using scanning electron microscopy. Microarray, RNA-seq and quantitative reverse transcription polymerase chain reaction (RT-qPCR) were used to identify regulators of bud formation. Gene function was characterized by down-regulation and overexpression. Overexpression of miR156 induced aerial bud formation in switchgrass. Various analyses revealed that SQUAMOSA PROMOTER BINDING PROTEIN LIKE4 (SPL4), one of the miR156 targets, directly regulated aerial axillary bud initiation. Down-regulation of SPL4 promoted aerial bud formation and increased basal buds, while overexpression of SPL4 seriously suppressed bud formation and tillering. RNA-seq and RT-qPCR identified potential downstream genes of SPL4. Unlike all previously reported genes acting as activators of basal bud initiation, SPL4 acts as a suppressor for the formation of both aerial and basal buds. The miR156-SPL4 module predominantly regulates aerial bud initiation and partially controls basal bud formation. Genetic manipulation of SPL4 led to altered plant architecture with increased branching, enhanced regrowth after cutting and improved biomass yield.

Pyrolysis of dedicated bioenergy crops grown on reclaimed mine land in West Virginia

Dedicated bioenergy crops grown on marginal lands such as reclaimed mine lands and other non-arable lands are auspicious cellulosic sources for sustainable bioenergy production. In this study, characterization of pyrolysis products were documented for two dedicated bioenergy crops grown on reclaimed coal-mine lands in West Virginia. Two clonal varieties (Private and Public varieties) of Miscanthus (Miscanthus x giganteus) and two varieties (Bomaster and Kanlow varieties) of Switchgrass (Panicum virgatum L) were used in this study. The oven-dried samples were pyrolyzed in a fixed-bed batch reactor under an inert condition and at a temperature of 500°C to produce biochar and bio-oil (vapor condensate). The pyrolysis product, energy and carbon conversion yields were calculated. Additionally, biochar and bio-oil were characterized for elemental composition, volatile, ash and calorific values. Results showed that there was no significant difference in the biochar yields (about 30.00% yield) obtained from the clonal varieties of Switchgrass and Miscanthus. The bio-oil yields were in the range of 45.00–51.00% with the Miscanthus (Private variety) having the highest bio-oil yield of 50.61%. The carbon content of the biomass, biochar and bio-oil were found to be 46.80–48.02%, 77.72–80.23% and 54.68–59.68%, respectively. Average calorific values were found to be 19.49MJ/kg, 29.01MJ/kg and 24.98MJ/kg for the biomass, biochar and bio-oil, respectively. Results for the surface chemistry of the biochars showed carbon and oxygen to be the major chemical constituents of the surfaces of the biochars. Carbon dioxide (CO2), nitrogen (N2) and carbon monoxide (CO) were found to be the major components of the non-condensable gas and the CO:CO2 ratio showed that the non-condensable gas cannot be used as a fluidizing medium.