GCB Bioenergy
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Impact of drought stress on growth and quality of miscanthus for biofuel production Abstract Miscanthus has a high potential as a biomass feedstock for biofuel production. Drought tolerance is an important breeding goal in miscanthus as water deficit is a common abiotic stress and crop irrigation is in most cases uneconomical. Drought may not only severely reduce biomass yields, but also affect biomass quality for biofuel production as cell wall remodeling is a common plant response to abiotic stresses. The quality and plant weight of 50 diverse miscanthus genotypes were evaluated under control and drought conditions (28 days no water) in a glasshouse experiment. Overall, drought treatment decreased plant weight by 45%. Drought tolerance – as defined by maintenance of plant weight – varied extensively among the tested miscanthus genotypes and ranged from 30% to 110%. Biomass composition was drastically altered due to drought stress, with large reductions in cell wall and cellulose content and a substantial increase in hemicellulosic polysaccharides. Stress had only a small effect on lignin content. Cell wall structural rigidity was also affected by drought conditions; substantially higher cellulose conversion rates were observed upon enzymatic saccharification of drought‐treated samples with respect to controls. Both cell wall composition and the extent of cell wall plasticity under drought varied extensively among all genotypes, but only weak correlations were found with the level of drought tolerance, suggesting their independent genetic control. High drought tolerance and biomass quality can thus potentially be advanced simultaneously. The extensive genotypic variation found for most traits in the evaluated miscanthus germplasm provides ample scope for breeding of drought‐tolerant varieties that are able to produce substantial yields of high‐quality biomass under water deficit conditions. The higher degradability of drought‐treated samples makes miscanthus an interesting crop for the production of second‐generation biofuels in marginal soils.
GCB Bioenergy - Tập 9 Số 4 - Trang 770-782 - 2017
Polycyclic aromatic hydrocarbons and volatile organic compounds in biochar and biochar‐amended soil: a review Abstract Residual pollutants including polycyclic aromatic hydrocarbons (PAH s), volatile organic compounds (VOC s), and carbon (aceous) nanoparticles are inevitably generated during the pyrolysis of waste biomass and remain on the solid coproduct called biochar. Such pollutants could have adverse effects on the plant growth as well as microbial community in soil. Although biochar has been proposed as a ‘carbon negative strategy’ to mitigate the greenhouse gas emissions, the impacts of its application with respect to long‐term persistence and bioavailability of hazardous components are not clear. Moreover, the co‐occurrence of low molecular weight VOC s with PAH s in biochar may exert further phytotoxic effects. This review describes the basic need to unravel key mechanisms driving the storage vs. emission of these organics and the dynamics between the sorbent (biochar) and soil microbes. Moreover, there is an urgent need for standardized methods for quantitative analysis of PAH s and VOC s in biochar under environmentally relevant conditions. This review is also extended to cover current research gaps including the influence of biochar application on the short‐ and long‐term fate of PAHs and VOCs and the proper control tactics for biochar quality and associated risk.
GCB Bioenergy - Tập 9 Số 6 - Trang 990-1004 - 2017
Evaluating a sustainability index for nutrients in a short rotation energy cropping system Abstract In dryland environments 3–5 year rotations of tree crops and agriculture represent a major potential bioenergy feedstock and a means to restore landscape hydrologic balances and phytoremediate sites, while maintaining food production. In soils with low natural fertility, the long‐term viability of these systems will be critically affected by site nutrient status and subsequent cycling of nutrients. A nutrient assimilation index (NAI ) was developed to allow comparison of species and tree component nutrient assimilation and to optimize nutrient management, by quantifying different strategies to manage site nutrients. Biomass, nutrient export and nutrient use efficiency were assessed for three short rotation tree crop species. Nutrient exports following harvest at 3 years of high density (4000 trees ha−1 ) were consistently higher in Pinus radiata , with values of 85 kg ha−1 of N, 11kg ha−1 of P, and 62 kg ha−1 of K, than Eucalyptus globulus and Eucalyptus occidentalis . Component NAI was generally in the order of leaf<twig<bark<root<stem‐wood for N, P, K, S, Ca, and Mg. The NAI ranged from 0.06 Mg kg−1 for N in leaves of P. radiata to 4.7 Mg kg−1 for P in stem‐wood of E. occidentalis , indicating higher sustainability of wood biomass compared with leaf biomass. The leaves for each species contained between 40 and 60% of the total nutrient contents while comprising around 25–30% of the total biomass. These nutrient exports via biomass removal are similar to those that follow 3 years of wheat production in the same region, indicating there is no additional drawdown of nutrient reserves during the tree cropping phase of the rotation.
GCB Bioenergy - Tập 5 Số 3 - Trang 315-326 - 2013
Comparing the potential production and value of high‐energy liquid fuels and protein from marine and freshwater macroalgae Abstract The biomass production and biochemical properties of marine and freshwater species of green macroalgae (multicellular algae), cultivated in outdoor conditions, were evaluated to assess the potential conversion into high‐energy liquid biofuels, specifically biocrude and biodiesel and the value of these products. Biomass productivities were typically two times higher for marine macroalgae (8.5–11.9 g m−2 d−1 , dry weight) than for freshwater macroalgae (3.4–5.1 g m−2 d−1 , dry weight). The biochemical compositions of the species were also distinct, with higher ash content (25.5–36.6%) in marine macroalgae and higher calorific value (15.8–16.4 MJ kg−1 ) in freshwater macroalgae. Lipid content was highest for freshwaterOedogonium and marineDerbesia . Lipids are a critical organic component for biocrude production by hydrothermal liquefaction (HTL ) and the theoretical biocrude yield was therefore highest forOedogonium (17.7%, dry weight) andDerbesia (16.2%, dry weight). Theoretical biocrude yields were also higher than biodiesel yields for all species due to the conversion of the whole organic component of biomass, including the predominant carbohydrate fraction. However, all marine species had higher biomass productivities and therefore had higher projected biocrude productivities than freshwater species, up to 7.1 t of biocrude ha−1 yr−1 forDerbesia . The projected value of the six macroalgae was increased by 45–77% (up toUS $7700 ha−1 yr−1 ) through the extraction of protein prior to the conversion of the residual biomass to biocrude. This study highlights the importance of optimizing biomass productivities for high‐energy fuels and targeting additional coproducts to increase value.
GCB Bioenergy - Tập 7 Số 4 - Trang 673-689 - 2015
Integrated lignocellulosic value chains in a growing bioeconomy: Status quo and perspectives Abstract Lignocellulose is the most abundant biomass on Earth, with an estimated 181.5 billion tonnes produced annually. Of the 8.2 billion tonnes that are currently used, about 7 billion tonnes are produced from dedicated agricultural, grass and forest land and another 1.2 billion tonnes stem from agricultural residues. Economic and environmentally efficient pathways for production and utilization of lignocellulose for chemical products and energy are needed to expand the bioeconomy. This opinion paper arose from the research network “Lignocellulose as new resource platform for novel materials and products” funded by the German federal state of Baden‐Württemberg and summarizes original research presented in this special issue. It first discusses how the supply of lignocellulosic biomass can be organized sustainably and suggests that perennial biomass crops (PBC) are likely to play an important role in future regional biomass supply to European lignocellulosic biorefineries. Dedicated PBC production has the advantage of delivering biomass with reliable quantity and quality. The tailoring of PBC quality through crop breeding and management can support the integration of lignocellulosic value chains. Two biorefinery concepts using lignocellulosic biomass are then compared and discussed: the syngas biorefinery and the lignocellulosic biorefinery. Syngas biorefineries are less sensitive to biomass qualities and are technically relatively advanced, but require high investments and large‐scale facilities to be economically feasible. Lignocellulosic biorefineries require multiple processing steps to separate the recalcitrant lignin from cellulose and hemicellulose and convert the intermediates into valuable products. The refining processes for high‐quality lignin and hemicellulose fractions still need to be further developed. A concept of a modular lignocellulosic biorefinery is presented that could be flexibly adapted for a range of feedstock and products by combining appropriate technologies either at the same location or in a decentralized form.
GCB Bioenergy - Tập 11 Số 1 - Trang 107-117 - 2019
Experimental evidence for sequestering C with biochar by avoidance of <scp>CO</scp><sub>2</sub> emissions from original feedstock and protection of native soil organic matter Abstract There is a need for further studies to compare the decomposition of biochar to that of the original feedstock and determine how these amendments affect the cycling of native organic matter (NOM ) of different soils to improve our understanding of the resulting net C sequestration potential. A 510‐days incubation experiment was conducted (i) to investigate the evolution of CO 2 from soils amended with either fresh corn stover (CS ) or with biochars produced from fresh CS at either 350 (CS ‐350) or 550 °C (CS ‐550), and (ii) to evaluate the priming effect of these amendments on NOM decomposition. Two soil types were studied: an Alfisol and an Andisol, with organic C contents of 4% and 10%, respectively. Except for the controls (with no C addition), all treatments received 7.18 t C ha−1 . We measured C efflux in short‐term intervals and its isotopic signature to distinguish between C evolved from C4 amendments and C3 ‐dominated NOM . Emission rates were then integrated for the whole time period to cover total emissions. Total CO 2 ‐C evolved from the original C in fresh CS , CS ‐350 and CS ‐550 was greater in the Andisol (78%, 13% and 14%) than in the Alfisol (66%, 8% and 7%). For both soils, (i) no significant differences (P > 0.05) were observed in the rate of CO 2 evolution between controls and biochar treatments; and (ii) total accumulated CO 2 evolved from the uncharred amendment was significantly higher (P < 0.05) than that from the other treatments. In the Alfisol, a significant (P < 0.05) net positive priming effect on NOM decomposition was observed when amended with fresh CS , while the opposite was detected in biochar treatments. In the Andisol, no significant (P > 0.05) net priming effect was observed. A C balance indicated that the C lost from both biochar production and decomposition ‘broke even’ with that lost from fresh residue decomposition after <35 weeks. The ‘break‐even’ point was reached earlier in the Andisol, in which the fresh CS mineralizes faster. These results provided experimental evidence for the potential of biochar to sequester C and avoid CO 2 emissions from original feedstock while protecting native soil organic matter.
GCB Bioenergy - Tập 7 Số 3 - Trang 512-526 - 2015
Characterization of <i>Miscanthus</i> cell wall polymers Abstract Efficient utilization of lignocellulosic Miscanthus biomass for the production of biochemicals, such as ethanol, is challenging due to its recalcitrance, which is influenced by the individual plant cell wall polymers and their interactions. Lignocellulosic biomass composition differs depending on several factors, such as plant age, harvest date, organ type, and genotype. Here, four selected Miscanthus genotypes (Miscanthus sinensis , Miscanthus sacchariflorus , Miscanthus × giganteus , Miscanthus sinensis × Miscanthus sacchariflorus hybrid) were grown and harvested, separated into stems and leaves, and characterized for their non‐starch polysaccharide composition and structures, lignin contents and structures, and hydroxycinnamate profiles (monomers and ferulic acid dehydrodimers). Polysaccharides of all genotypes are mainly composed of cellulose and low‐substituted arabinoxylans. Ratios of hemicelluloses to cellulose were comparable, with the exception of Miscanthus sinensis that showed a higher hemicellulose/cellulose ratio. Lignin contents of Miscanthus stems were higher than those of Miscanthus leaves. Considering the same organs, the four genotypes did not differ in their Klason lignin contents, but Miscanthus × giganteus showed the highest acetylbromide soluble lignin content. Lignin polymers isolated from stems varied in their S/G ratios and linkage type distributions across genotypes. p ‐Coumaric acid was the most abundant ester‐bound hydroxycinnamte monomer in all samples. Ferulic acid dehydrodimers were analyzed as cell wall cross‐links, with 8‐5‐coupled diferulic acid being the main dimer, followed by 8‐O‐4‐, and 5‐5‐diferulic acid. Contents of p ‐coumaric acid, ferulic acid, and ferulic acid dimers varied depending on genotype and organ type. The largest amount of cell wall cross‐links was analyzed for Miscanthus sinensis .
GCB Bioenergy - Tập 11 Số 1 - Trang 191-205 - 2019
Evaluation of <i>Miscanthus sinensis</i> biomass quality as feedstock for conversion into different bioenergy products Abstract Miscanthus is a promising fiber crop with high potential for sustainable biomass production for a biobased economy. The effect of biomass composition on the processing efficiency of miscanthus biomass for different biorefinery value chains was evaluated, including combustion, anaerobic digestion and enzymatic saccharification for the production of bioethanol. Biomass quality and composition was analyzed in detail using stem and leaf fractions of summer (July) and winter (March) harvested biomass of eight compositionally diverse Miscanthus sinensis genotypes. Genotype performance in tests for enzymatic saccharification, anaerobic digestion and combustion differed extensively. The variation between the best and the worst performing genotype was 18% for biogas yield (ml g−1 dm) and 42% for saccharification efficiency (glucose release as %dm). The ash content of the best performing genotype was 62% lower than that of the genotype with the highest ash content and showed a considerably high ash melting temperature during combustion. Variation between genotypes in biomass quality for the different thermochemical bioconversion processes was shown to be strongly correlated to differences in biomass composition. The most important traits that contributed favorably to biogas yields and saccharification efficiency were a high content of trans ‐ferulic acid, a high ratio of para ‐coumaric acid to lignin and a low lignin content. Additionally, a high content of hemicellulosic polysaccharides positively affected saccharification efficiency. Low contents of ash and inorganic elements positively affect biomass quality for combustion and low potassium and chloride contents contributed to a higher ash melting temperature. These results demonstrate the potential for optimizing and exploiting M. sinensis as a multipurpose lignocellulosic feedstock, particularly for bioenergy applications.
GCB Bioenergy - Tập 9 Số 1 - Trang 176-190 - 2017
Yields of <i><scp>M</scp>iscanthus</i> × <i>giganteus</i> and <i><scp>P</scp>anicum virgatum</i> decline with stand age in the Midwestern <scp>USA</scp> Abstract For the C4 perennial grasses, M iscanthusgiganteus and Panicum virgatum (switchgrass) to be successful for bioenergy production they must maintain high yields over the long term. Previous studies under the less conducive climate for productivity in N.W. Europe found little or no yield decline in M giganteus in the long term. This study provides the first analysis of whether yield decline occurs in M giganteus under United States. Midwest conditions in side‐by‐side trials with P . virgatumM iscanthusgiganteus produced yields more than twice that of P . virgatum−1 yr−1 and 10.0 ± 0.9 Mg ha−1 yr−1 , respectively, averaged over 8–10 years. Relationships of yield with precipitation and growing degree days were established and used to estimate yields corrected for the stochastic effects of weather. Across all locations and in both species, yield initially increased until it reached a maximum during the fifth growing season and then declined to a stable, but lower level in the eighth. This pattern was more pronounced in M giganteus . The mean yields observed over this longer term period of 8–10 years were lower than the yields of the first 5 years. However, this decline was proportionately greater in M giganteus than in P . virgatum,M giganteus . Based on the average yield over the period of this study, meeting the United States Renewable Fuel Standard mandate of 60 billion liters of cellulosic ethanol by 2022, would require 6.8 Mha of M giganteus or 15.8 Mha of P . virgatum
GCB Bioenergy - Tập 6 Số 1 - Trang 1-13 - 2014
Contribution of above‐ and belowground bioenergy crop residues to soil carbon Abstract GHG mitigation by bioenergy crops depends on crop type, management practices, and the input of residue carbon (C) to the soil. Perennial grasses may increase soil C compared to annual crops because of more extensive root systems, but it is less clear how much soil C is derived from above‐ vs. belowground inputs. The objective of this study was to synthesize the existing knowledge regarding soil C inputs from above‐ and belowground crop residues in regions cultivated with sugarcane, corn, and miscanthus, and to predict the impact of residue removal and tillage on soil C stocks. The literature review showed that aboveground inputs to soil C (to 1‐m depth) ranged from 70% to 81% for sugarcane and corn vs. 40% for miscanthus. Modeled aboveground C inputs (to 30 cm depth) ranged from 54% to 82% for sugarcane, but were 67% for miscanthus. Because 50% of observed miscanthus belowground biomass is below 30 cm depth, it may be necessary to increase the depth of modeled soil C dynamics to reconcile modeled belowground C inputs with measured. Modeled removal of aboveground corn residue (25–100%) resulted in C stock reduction in areas of corn–corn–soybean rotation under conventional tillage, while no‐till management lessoned this impact. In sugarcane, soil C stocks were reduced when total aboveground residue was removed at one site, while partial removal of sugarcane residue did not reduce soil C stocks in either area. This study suggests that aboveground crop residues were the main C‐residue source to the soil in the current bioethanol sector (corn and sugarcane) and the indiscriminate removal of crop residues to produce cellulosic biofuels can reduce soil C stocks and reduce the environmental benefits of bioenergy. Moreover, a switch to feedstocks such as miscanthus with more allocation to belowground C could increase soil C stocks at a much faster rate.
GCB Bioenergy - Tập 9 Số 8 - Trang 1333-1343 - 2017
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