Bioenergy Crops Research Articles

Biomass production from energy and fast growing plants

The agro-ecological and soil conditions of the Republic of Srpska provide the possibility of growing many agro-energy crops, which represent a great chance for agricultural producers who own lands with less favorable physical and chemical properties. The production and spreading of bioenergy crops have been exposed to sharply critics and suspicion for their economic justification. The basic problem is the identification of the most suitable biomass and the projecting of the process by which the energy from it should be extracted. Using the produced biomass would significantly reduce the consumption of fossil fuels, which Serbia and Republic of Srpska have in limited quantities. The great genetic potential of fertility has classified miscanthus in the group of the most important bio-energetic crops. By introducing these predominantly perennial plants into production, with slightly higher investments in the year of establishment and significantly less in the years of use, uncultivated agricultural land could be used and also the most non-agricultural areas and deposoles could be bring to purpose. Fresh above-ground biomass of miscanthus and Spanish reed plants, mowed in the panicle phenophase, is used to obtain biogas, while dry baled stalks without leaves are burned directly in cauldron plants (for example in thermal power plants) or used for the production of briquettes. The advantage of using miscanthus and Spanish reed for bio-fuel production compared to other field plants is their higher yield and higher amount of fuel obtained per unit area and, on the other hand, quantity of world food production is not reduced, because this species participates little in world needs for food of plant origin.

THE DISTRIBUTION OF CASH EXPENSES FOR THE CREATION OF BIOENERGY WILLOW PLANTATIONS IN UKRAINE

The economic cost analysis of creating energy willow plantations in Ukraine is provided in the present paper. The experience of creating bioenergy willow plantations at scientific and industrial institutions in Ukraine has been used in the paper. The purpose of this scientific work is to conduct an analysis of the structure of cash expenses for the creation of bioenergy willow plantations based on the experience of various institutions of Ukraine. The analysis is based on a technological map created during the study on drained peat lands at Panfyly Research Station. Analyzing the cost structure by category, the data obtained during the creation of bioenergy willow plantations of Salix Energy LLC and the Institute of Bioenergy Crops and Sugar Beet were also taken into account. After analyzing all the technology stages of growing bioenergy willow, it was revealed that the most expensive is the second stage associated with the preparation for planting and planting willow cuttings in the context of the pricing policy in Ukraine. In general, more than 60% of all expenses fall upon the first year of cultivation. According to the experience of Ukrainian institutions, the cost structure will have a significant shift towards planting material - 55-60%. The remaining costs are distributed during the use of equipment in the field, which constitute 26-30% and transportation costs respectively are 12-19%.

Drought Impact on the Morpho-Physiological Parameters of Perennial Rhizomatous Grasses in the Mediterranean Environment

The selection of non-food crops for bioenergy production in limiting environments is a priority for energy security and climate change mitigation. Therefore, more studies are needed on the interactions between species and environmental factors in specific sites which allows their selection for biomass production. The objective of this work is to study the impact of drought on the morpho-physiological parameters of perennial rhizomatous grasses Panicum virgatum L., Miscanthus × giganteus, and Arundo donax L. in the Mediterranean environment. Plants were grown on field and trials were carried out under support-irrigation and rainfed conditions during two consecutive years. Morpho-physiological parameters were measured in May, June and August, and dry biomass at the end of the experiment. Under rainfed conditions, A. donax presented the highest photosynthesis rate (25, 15 and 10 CO2 m−2 s−1), relative water content (85–90%), and dry biomass (~4500 g plant−1) compared with P. virgatum (20, 5 and 5 CO2 m−2 s−1, 65–85% RWC and ~1400 g plant−1) and Miscanthus (18, 4 and 0 CO2 m−2 s−1, 80–10% RWC and ~260 g plant−1). It is concluded that A. donax would be the best perennial rhizomatous grass to be used as bioenergy crop under Mediterranean conditions.

Systematic approaches to C-lignin engineering in Medicago truncatula

BackgroundC-lignin is a homopolymer of caffeyl alcohol present in the seed coats of a variety of plant species including vanilla orchid, various cacti, and the ornamental plant Cleome hassleriana. Because of its unique chemical and physical properties, there is considerable interest in engineering C-lignin into the cell walls of bioenergy crops as a high-value co-product of bioprocessing. We have used information from a transcriptomic analysis of developing C. hassleriana seed coats to suggest strategies for engineering C-lignin in a heterologous system, using hairy roots of the model legume Medicago truncatula.ResultsWe systematically tested strategies for C-lignin engineering using a combination of gene overexpression and RNAi-mediated knockdown in the caffeic acid/5-hydroxy coniferaldehyde 3/5-O-methyltransferase (comt) mutant background, monitoring the outcomes by analysis of lignin composition and profiling of monolignol pathway metabolites. In all cases, C-lignin accumulation required strong down-regulation of caffeoyl CoA 3-O-methyltransferase (CCoAOMT) paired with loss of function of COMT. Overexpression of the Selaginella moellendorffii ferulate 5-hydroxylase (SmF5H) gene in comt mutant hairy roots resulted in lines that unexpectedly accumulated high levels of S-lignin.ConclusionC-Lignin accumulation of up to 15% of total lignin in lines with the greatest reduction in CCoAOMT expression required the strong down-regulation of both COMT and CCoAOMT, but did not require expression of a heterologous laccase, cinnamyl alcohol dehydrogenase (CAD) or cinnamoyl CoA reductase (CCR) with preference for 3,4-dihydroxy-substituted substrates in M. truncatula hairy roots. Cell wall fractionation studies suggested that the engineered C-units are not present in a heteropolymer with the bulk of the G-lignin.

Dodder Parasitism Leads to the Enrichment of Pathogen Alternaria and Flavonoid Metabolites in Soybean Root

Dodders (Cuscuta chinensis) are rootless and holoparasitic herbs that can infect a variety of host plants, including the vitally important economic and bioenergy crop soybean (Glycine max). Although dodder parasitism severely affects the physiology of host plants, little is known about its effects on fungal communities and root secondary metabolites in hosts. In this study, variations in root-associated fungal communities and root metabolites of soybean under different parasitism conditions were investigated using ITS rRNA gene sequencing and UPLC–MS/MS metabolome detection technologies. The results showed that dodder parasitism significantly altered the composition and diversity of the fungal communities in the rhizosphere and endosphere of soybean. The relative abundance of the potential pathogenic fungus Alternaria significantly increased in the root endosphere of dodder-parasitized soybean. Furthermore, correlation analysis indicated that the fungal community in the root endosphere was susceptible to soil factors under dodder parasitism. Meanwhile, the content of soil total nitrogen was significantly and positively correlated with the relative abundance of Alternaria in the rhizosphere and endosphere of soybean. Metabolomic analysis indicated that dodder parasitism altered the accumulation of flavonoids in soybean roots, with significant upregulation of the contents of kaempferol and its downstream derivatives under different parasitism conditions. Taken together, this study highlighted the important role of dodder parasitism in shaping the fungal communities and secondary metabolites associated with soybean roots, providing new insights into the mechanisms of multiple interactions among dodder, soybean, microbial communities and the soil environment.

First report of post-harvest tuber rot of Apios americana Medikus caused by Penicillium expansum in South Korea.

Apios americana Medikus, a perennial vine legume native to North America, is known as 'Indian potato' or 'Apios' for their underground tubers that are used for human consumption in Korea (Choi et al., 2017). These tubers are known to be rich in isoflavones as well as other secondary products to have known several medicinal properties (Chu et al., 2019). The harvested tubers in 2020 were observed to rot during storage of tubers for 4 months at 4°C in the genetic resource storage room at the Bioenergy Crop Research Institute, National Institute of Crop Science, Muan, Jeollanam-do, South Korea. The incidence of rot symptoms with blue mold was less than 1% per 20 kg box. Ten infected tubers were collected from several boxes and the lesions were cut into small pieces, and then surface sterilized in 1.5% NaClO for 2 minutes, followed by rinsing 3 times with sterilized water. To investigate their morphological characteristics, ten isolates were cultured in Malt Extract Agar (MEA) medium at 25° C for 5 days (Pitt and Hocking, 1988). The surface morphology of the mycelium had white or light green fluffy, and completely blue spores were formed after about 5 days. The conidia were one-stage branched with an elliptical shape, about 3.5 to 4.3 × 2.9 to 3.6 (mean 3.8 ± 0.3 × 3.2 ± 0.2) ㎛ in diameter (n=30). Genomic DNAs of the isolates were extracted using Solgent DNA Extraction Kit (Solgent, Daejeon, Korea), and then PCR products of the internal transcribed spacer (ITS1/ITS4) region and the beta-tubulin gene (Bt2a/Bt2b) were sequenced and analyzed (Glass and Donaldson, 1995). The BLASTn showed that the representative isolate had 99% homology with reference Penicillium expansum strain ICMP 2708 (ITS region and TUB2 gene) in NCBI GenBank. The sequences of the isolate were deposited in GenBank as accession numbers MZ636667 and MZ702813 for ITS and TUB2 genes, respectively. Based on the morphological characteristics and molecular analysis, the isolate was identified as P. expansum. Pathogenicity assays of the isolate were also performed using three tubers in three replicates inoculated with spore suspension (concentration, 1×106 conidia/mL) and compared with a control group inoculated with sterilized water. The inoculated Apios tubers were placed in a plastic box maintained in conditions of high humidity at 25°C. Five days after inoculation, the typical symptoms were observed on inoculated tubers, and no symptoms were observed in the control one. P. expansum was again isolated from artificially inoculated tubers to complete Koch's assumption. This is the first report of P. expansum causing tuber rot in A. americana in South Korea. As the cultivated area of Apios is increasing in Korea, it will be necessary to develop effective storage methods and management strategies for the control of storage diseases such as blue mold.

Field performance of switchgrass plants engineered for reduced recalcitrance.

Switchgrass (Panicum virgatum L.) is a promising perennial bioenergy crop that achieves high yields with relatively low nutrient and energy inputs. Modification of cell wall composition for reduced recalcitrance can lower the costs of deconstructing biomass to fermentable sugars and other intermediates. We have engineered overexpression of OsAT10, encoding a rice BAHD acyltransferase and QsuB, encoding dehydroshikimate dehydratase from Corynebacterium glutamicum, to enhance saccharification efficiency in switchgrass. These engineering strategies demonstrated low lignin content, low ferulic acid esters, and increased saccharification yield during greenhouse studies in switchgrass and other plant species. In this work, transgenic switchgrass plants overexpressing either OsAT10 or QsuB were tested in the field in Davis, California, USA for three growing seasons. No significant differences in the content of lignin and cell wall-bound p-coumaric acid or ferulic acid were detected in transgenic OsAT10 lines compared with the untransformed Alamo control variety. However, the transgenic overexpressing QsuB lines had increased biomass yield and slightly increased biomass saccharification properties compared to the control plants. This work demonstrates good performance of engineered plants in the field, and also shows that the cell wall changes in the greenhouse were not replicated in the field, emphasizing the need to validate engineered plants under relevant field conditions.

Nutrient requirement of switchgrass (Panicum virgatum L.) cultivated on marginal land of the Right Bank Forest Steppe of Ukraine

The study aimed to investigate the peculiarities of the nutrient requirement of switchgrass cultivated on marginal land under the application of lime, adsorbent and foliar application of fertilizers in the Right Bank Forest Steppe of Ukraine. The experiment was conducted in the Uladivka-Liulyntsi Experimental Breeding Station of the Institute of Bioenergy Crops and Sugar Beet National Academy of Agrarian Sciences in 2019−2022. The soil of the experimental field was deep, leached, sandy, medium-loamy chernozem with low humus content in the 0−30 cm layer (3.9 %). Mineral nitrogen content was as following: 16.4 mg/kg (nitrate) and 38.7 mg/kg (ammonium). Mbile phosphorusav ailability was low (8.3 mg/kg), while the content of exchange potassium was high −10.3 mg/kg. Soil pH was 5.1, and hydrolytic acidity was high − 4.2 mg eq/100 g. Application of lime (25 % of the required rate), MaxiMarin granulated adsorbent and foliar fertilizer aimed at the alleviation of plant stress related to soil acidity and formation of high productivity of plantations taking into account nutrient removal with harvested biomass. In the experiment, the nitrogen removal was 57.5 kg/ha, phosphorus 39.3 kg/ha and potassium 118.7 kg/ha, while 25.0 kg/ha of nitrogen, 17.6 kg/ha of phosphorus and 55.8 kg/ha of potassium was returned to the soil with harvest residues. The application of the studied agronomic practices led to an increase in both the removal and recycling of nutrients. In the 4th vegetation season, nutrient recycling of switchgrass (% to the nutrient removal) made up 43.6 % of nitrogen, 44.7 % of phosphorus and 47.0 % of potassium from the total removal of the crop were returned to the soil. Key words: liming, adsorbent, foliar application of fertilizers.

Productivity of giant miscanthus plantations depending on the applied elements of cultivation technology in the conditions of the Forest Steppe of Ukraine

Purpose. To improve the technology of caring for giant miscanthus plantations, starting from the second year of the crop vegetation, and to establish the peculiarities of the formation of biomass yield with the use of different types of fertilizers. Methods. The research was carried out in the years 2020–2021 in the conditions of the Bila Tserkva Experimental and Breeding Station of the Institute of Bioenergy Crops and Sugar Beet of the National Academy of Agrarian Sciences located in the zone of unstable moisture of the Right Bank Forest Steppe of Ukraine. The design of the experiment involved the application of mineral fertilisers (ammonium nitrate N24 kg/ha a. i., ammonium nitrate + ammonium sulfate N24 + S6 kg/ha a. i.) in row in the spring, foliar application of humates (Vermisol, 8.0 l/ha, Humifield VR-18, 0.4 l/ha), and complex fertiliser with amino acids (Quantum Aminomax, 0.5 l/ha). Mineral fertilizers were applied locally in row before the emergence of miscanthus seedlings. Split foliar application of humates and amino acids was carried out in the five-leaf stage and two weeks later. Results. Productivity of miscanthus plants differed significantly over growing seasons, while the main regularities of the influence of the investigated elements of plantation care technology on the productivity formation were maintained. In the second year of vegetation (2020), each plant formed from 18 to 37 shoots and in the third year from 37 to 50 shoots. Four-year-old plants had 28–50 shoots each. The yield of raw biomass at the end of the growing season in 2020 varied from 14.5 to 43.5 t/ha. Compared to 2020, in 2021 the biomass yield increased 1.5–2 times – up to 31.0–74.6 t/ha. According to the experiment, the average yield of biomass for the fourth year of the growing was 17% lower compared to the respective indicators of 2021 and varied according to the experiment treatments from 25.3 to 67.1 t/ha. The yield of dry matter varied from 9.78 to 28.30 t/ha in 2020, from 17.50 to 37.85 t/ha in 2021, and from 12.11 to 32.46 t/ha in 2022. The estimated energy output from miscanthus biomass, depending on the influence of the experimental factors, was 174.8–509.6 GJ/ha in 2020, 315.5–683.2 GJ/ha in 2021, and in 2022 – 219.0–587.3 GJ/ha. Conclusions. The minimum values of all studied productivity indicators of miscanthus were obtained in the control treatment of the experiment. Application of ammonium nitrate (N24) and ammonium nitrate with ammonium sulfate (N24 + S6) in spring contributed to a significant increase in the number of shoots per plant, as well as biomass yield and estimated energy yield per hectare. Similarly, significant increase in all indicators of productivity was ensured by foliar application of humates (Humifield BP-18, 0.4 l/ha and Vermisol, 8,0 l/ha). In general, over the years of research, the maximum indicators of the number of shoots per plant, the yield of biomass and the estimated energy output from biomass were obtained under the combined application of mineral fertilisers [ammonium nitrate + ammonium sulfate (N24 + S6)] with two-time foliar application of humates (Vermisol, 8.0 l/ha or Humifield VR-18, 0.4 l/ha) and complex fertiliser Quantum Aminomax, 0.5 l/ha.

Formation of the above-ground biomass of willow under the influence of varietal characteristics and the type of planting material

Purpose. To reveal the regularities of the formation of the energy willow above-ground biomass structure and evaluate the qualitative and quantitative indicators of the biomass components under the effect of varietal characteristics and the type of planting material.
 Methods. Field experiments were conducted at the experimental field of the Institute of Bioenergy Crops and Sugar Beet (Ksaverivka 2, Kyiv region) located in the zone of unstable moisture in the central part of the Right Bank Forest Steppe of Ukraine in 2019–2022. Cuttings and shoots were harvested in autumn and stored in various ways until planting. In the spring, after planting the shoots in the open ground, the biometric parameters of plants were determined: plant height, stem diameter and the number of stems. The measurements were taken on the same day every month during the three years of the experiment. Two willow varieties were used in the experiment: Salix triandra L. variety 'Panfylska' and S. viminalis L. variety 'Zbruch'.
 Results. The intensity of growth of the above-ground biomass of willow, which also depends on the yield of planting material (cuttings or shoots), was determined by plant height, stem diameter and the number of stems. These indicators were higher in 'Zbruch' compared to 'Panfylska'. Thus, in the second year of vegetation, on the first date of measuring (in spring), the plant height of 'Panfylska' variety was 136.3 cm, while in autumn. on September 21, it was 242.8 cm. In 'Zbruch', the indicators were higher by 12.4 and 13.5 cm, respectively. A similar dependence was found when planting shoots. It should be noted that within one variety, no regular and reliable difference in plant height depending on the type of planting material was found. In the third year of vegetation, a similar dependence of plant height on varietal characteristics was obtained. On average, in 2021–2022, when planting willow cuttings of 'Zbruch' variety, plant height was 276.1 cm in the spring, while in 'Panfylska' it was 20 cm lower (256.1 cm). In autumn, plant height was higher in 'Zbruch' also by 20 cm. Depending on the year of vegetation, the increase in plant height was the greatest in the first year of vegetation compared to the second and third years. Weather conditions during the growing season affected the height of plants; However, in all years of the research it was higher when planting cuttings and shoots of 'Zbruch' compared to 'Panfylska'. No significant influence of variety and the type of planting material on the stem diameter and the number of stems was found in all years of the research.
 Conclusions. Plant height and diameter of stem in dynamics depended on varietal characteristics. In 'Zbruch' variety, when planting cuttings and shoots, the increase in plant height and stem diameter was higher compared to 'Panfylska' both at the beginning of the growing season and in autumn. During the three years of vegetation, varietal characteristics and the type of planting material (cuttings and shoots) showed no significant difference in the plant height, stem diameter and the number of stems.

Accelerating the development of a sustainable bioenergy portfolio through stable isotopes

AbstractBioenergy could help limit global warming to 2°C above pre‐industrial levels while supplying almost a fourth of the world's renewable energy needs by 2050. However, the deployment of bioenergy raises concerns that adoption at meaningful scales may lead to unintended negative environmental consequences. Meanwhile, the full consolidation of a bioenergy industry is currently challenged by a sufficient, resilient, and resource‐efficient biomass supply and an effective conversion process. Here, we provide a comprehensive analysis of how stable isotope approaches have accelerated the development of a robust bioeconomy by advancing knowledge about environmental sustainability, feedstock development, and biological conversion. We show that advances in stable isotope research have generated crucial information to (1) gain mechanistic insight into the potential of bioenergy crops to mitigate climate change as well as their impact on water and nutrient cycling; (2) develop high‐yielding, resilient feedstocks that produce high‐value bioproducts in planta; and (3) engineer microbes to enhance feedstock conversion to bioenergy products. Further, we highlight knowledge gaps that could benefit from future research facilitated by stable isotope approaches. We conclude that advances in mechanistic knowledge and innovations within the field of stable isotopes in cross‐disciplinary research actions will greatly contribute to breaking down the barriers to establishing a robust bioeconomy.

Predicting Biomass Yields of Advanced Switchgrass Cultivars for Bioenergy and Ecosystem Services Using Machine Learning

The production of advanced perennial bioenergy crops within marginal areas of the agricultural landscape is gaining interest due to its potential to sustainably produce feedstocks for biofuels and bioproducts while also improving the sustainability and resilience of commodity crop production. However, predicting the biomass yields of this production system is challenging because marginal areas are often relatively small and spread around agricultural fields and are typically associated with various abiotic conditions that limit crop production. Machine learning (ML) offers a viable solution as a biomass yield prediction tool because it is suited to predicting relationships with complex functional associations. The objectives of this study were to (1) evaluate the accuracy of commonly applied ML algorithms in agricultural applications for predicting the biomass yields of advanced switchgrass cultivars for bioenergy and ecosystem services and (2) determine the most important biomass yield predictors. Datasets on biomass yield, weather, land marginality, soil properties, and agronomic management were generated from three field study sites in two U.S. Midwest states (Illinois and Iowa) over three growing seasons. The ML algorithms evaluated in the study included random forests (RFs), gradient boosting machines (GBMs), artificial neural networks (ANNs), K-neighbors regressor (KNR), AdaBoost regressor (ABR), and partial least squares regression (PLSR). Coefficient of determination (R2) and mean absolute error (MAE) were used to evaluate the predictive accuracy of the tested algorithms. Results showed that the ensemble methods, RF (R2 = 0.86, MAE = 0.62 Mg/ha), GBM (R2 = 0.88, MAE = 0.57 Mg/ha), and GBM (R2 = 0.78, MAE = 0.66 Mg/ha), were the most accurate in predicting biomass yields of the Independence, Liberty, and Shawnee switchgrass cultivars, respectively. This is in agreement with similar studies that apply ML to multi-feature problems where traditional statistical methods are less applicable and datasets used were considered to be relatively small for ANNs. Consistent with previous studies on switchgrass, the most important predictors of biomass yield included average annual temperature, average growing season temperature, sum of the growing season precipitation, field slope, and elevation. This study helps pave the way for applying ML as a management tool for alternative bioenergy landscapes where understanding agronomic and environmental performance of a multifunctional cropping system seasonally and interannually at the sub-field scale is critical.

PROSPECTS OF ROPE PROCESSING INTO BIODIESEL AS A DIRECTION FOR ENSURING THE ENERGY INDEPENDENCE OF THE AGRICULTURAL COMPLEX

The vision of domestic scientists in the field of production of biofuels from agro-biomass has been investigated in the article. The volumes of rapeseed production and the geographical structure of the export of this crop have been determined. The need to find ways to ensure the energy independence of the agricultural sector through the use of bioenergy crops has been established. The need to form the clusters for the production of biodiesel fuel in the composition of scientific research institutions, agricultural formations and manufacturers of equipment for the production of biodiesel has been determined. The need for further improvement of rapeseed cultivation technologies by applying organic fertilizers (digestate) is argued, which will make it possible to increase the yield of this crop, and the use of biodiesel – to reduce the cost of production. The technology of biodiesel fuel production on the basis of Vinnytsia National Agrarian University was studied and its economic feasibility was ascertained. It has been confirmed that the competitive production of biodiesel can create favorable conditions for the cultivation and sale of agricultural products for agricultural enterprises, so they should make the necessary adjustments in the tactics and strategy of their economic activities. The potential of rapeseed for processing in the amount of 2.67 million tons for biodiesel was determined. It is noted that appropriate production will make it possible to produce technical glycerin, which is also in demand on the market among cosmetics and pharmaceutical industry manufacturers. It was concluded that the application of the proposed measures will make it possible to: increase the GDP by UAH 20.2 billion; ensure partial energy independence of the agricultural sector; create additional jobs in rural areas; partially load distilleries with orders for technical alcohol (methanol); provide the livestock industry with concentrated fodder in the form of rape cake; reduce the cost of agricultural production due to the partial replacement of diesel fuel with biodiesel; partially satisfy the needs of the other sectors of the economy in energy resources.

Species selection determines carbon allocation and turnover in Miscanthus crops: Implications for biomass production and C sequestration

Growing Miscanthus species and hybrids has received strong scientific and commercial support, with the majority of the carbon (C) modelling predictions having focused on the high-yield, sterile and noninvasive hybrid Miscanthus × giganteus. However, the potential of other species with contrasting phenotypic and physiological traits has been seldom explored. To better understand the mechanisms underlying C allocation dynamics in these bioenergy crops, we pulse-labelled (13CO2) intact plant-soil systems of Miscanthus × giganteus (GIG), Miscanthus sinensis (SIN) and Miscanthus lutarioriparius (LUT) and regularly analysed soil respiration, leaves, stems, rhizomes, roots and soils for up to 190 days until leaf senescence. A rapid isotopic enrichment of all three species was observed after 4 h, with the amount of 13C fixed into plant biomass being inversely related to their respective standing biomass prior to pulse-labelling (i.e., GIG < SIN < LUT). However, both GIG and LUT allocated more photoassimilates in the aboveground biomass (leaves+stems = 78 % and 74 %, respectively) than SIN, which transferred 30% of fixed 13C in its belowground biomass (rhizomes+roots). Although less fixed 13C was recovered from the soils (<1 %), both rhizospheric and bulk soils were signficantly more enriched under SIN and LUT than under GIG. Importantly, the soils under SIN emitted less CO2, which suggests it could be the best choice for reaching C neutrality. These results from this unique large-scale study indicate that careful species selection may hold the success for reaching net GHG mitigation.

Drought-triggered leaf transcriptional responses disclose key molecular pathways underlying leaf water use efficiency in sugarcane (Saccharum spp.).

Drought is a major constraint to sugarcane (Saccharum spp.) production and improving the water use efficiency (WUE) is a critical trait for the sustainability of this bioenergy crop. The molecular mechanism underlying WUE remains underexplored in sugarcane. Here, we investigated the drought-triggered physiological and transcriptional responses of two sugarcane cultivars contrasting for drought tolerance, 'IACSP97-7065' (sensitive) and 'IACSP94-2094' (tolerant). After 21 days without irrigation (DWI), only 'IACSP94-2094' exhibited superior WUE and instantaneous carboxylation efficiency, with the net CO2 assimilation being less impacted when compared with 'IACSP97-7065'. RNA-seq of sugarcane leaves at 21 DWI revealed a total of 1,585 differentially expressed genes (DEGs) for both genotypes, among which 'IACSP94-2094' showed 617 (38.9%) exclusive transcripts (212 up- and 405 down-regulated). Functional enrichment analyses of these unique DEGs revealed several relevant biological processes, such as photosynthesis, transcription factors, signal transduction, solute transport, and redox homeostasis. The better drought-responsiveness of 'IACSP94-2094' suggested signaling cascades that foster transcriptional regulation of genes implicated in the Calvin cycle and transport of water and carbon dioxide, which are expected to support the high WUE and carboxylation efficiency observed for this genotype under water deficit. Moreover, the robust antioxidant system of the drought-tolerant genotype might serve as a molecular shield against the drought-associated overproduction of reactive oxygen species. This study provides relevant data that may be used to develop novel strategies for sugarcane breeding programs and to understand the genetic basis of drought tolerance and WUE improvement of sugarcane.

Genome-Resolved Metagenomics of Nitrogen Transformations in the Switchgrass Rhizosphere Microbiome on Marginal Lands

Switchgrass (Panicum virgatum L.) remains the preeminent American perennial (C4) bioenergy crop for cellulosic ethanol, that could help displace over a quarter of the US current petroleum consumption. Intriguingly, there is often little response to nitrogen fertilizer once stands are established. The rhizosphere microbiome plays a critical role in nitrogen cycling and overall plant nutrient uptake. We used high-throughput metagenomic sequencing to characterize the switchgrass rhizosphere microbial community before and after a nitrogen fertilization event for established stands on marginal land. We examined community structure and bulk metabolic potential, and resolved 29 individual bacteria genomes via metagenomic de novo assembly. Community structure and diversity were not significantly different before and after fertilization; however, the bulk metabolic potential of carbohydrate-active enzymes was depleted after fertilization. We resolved 29 metagenomic assembled genomes, including some from the ‘most wanted’ soil taxa such as Verrucomicrobia, Candidate phyla UBA10199, Acidobacteria (rare subgroup 23), Dormibacterota, and the very rare Candidatus Eisenbacteria. The Dormibacterota (formally candidate division AD3) we identified have the potential for autotrophic CO utilization, which may impact carbon partitioning and storage. Our study also suggests that the rhizosphere microbiome may be involved in providing associative nitrogen fixation (ANF) via the novel diazotroph Janthinobacterium to switchgrass.

Elongated galactan side chains mediate cellulose-pectin interactions in engineered Arabidopsis secondary cell walls.

The plant secondary cell wall is a thickened matrix of polysaccharides and lignin deposited at the cessation of growth in some cells. It forms the majority of carbon in lignocellulosic biomass, and it is an abundant and renewable source for forage, fiber, materials, fuels, and bioproducts. The complex structure and arrangement of the cell wall polymers mean that the carbon is difficult to access in an economical and sustainable way. One solution is to alter the cell wall polymer structure so that it is more suited to downstream processing. However, it remains difficult to predict what the effects of this engineering will be on the assembly, architecture, and properties of the cell wall. Here, we make use of Arabidopsis plants expressing a suite of genes to increase pectic galactan chain length in the secondary cell wall. Using multi-dimensional solid-state nuclear magnetic resonance, we show that increasing galactan chain length enhances pectin-cellulose spatial contacts and increases cellulose crystallinity. We also found that the increased galactan content leads to fewer spatial contacts of cellulose with xyloglucan and the backbone of pectin. Hence, we propose that the elongated galactan side chains compete with xyloglucan and the pectic backbone for cellulose interactions. Due to the galactan topology, this may result in comparatively weak interactions and disrupt the cell wall architecture. Therefore, introduction of this strategy into trees or other bioenergy crops would benefit from cell-specific expression strategies to avoid negative effects on plant growth.

Seasonal and regional changes in terrestrial carbon uptake under an overshoot scenario

Carbon dioxide removal (CDR) could change terrestrial carbon uptake due to biosphere responses. Here we examine the seasonal and regional responses of net biome productivity (NBP) and its components to carbon emissions reduction under the SSP5–3.4 overshoot scenario simulated by eight CMIP6 Earth system models. Globally averaged NBP is lower under SSP5–3.4 than under SSP5–8.5, with 102±7 Pg C (51%) less accumulated during 2041 to 2100. About 59% of accumulated change in NBP is from reduction in net ecosystem productivity in the boreal growing season, associated with the reduction in atmospheric CO2 concentrations and the resulting climate change. The rest of the accumulated reduction in NBP is due to greater disturbances from bioenergy crop expansion and land use change. These results imply that improved land management, more aggressive carbon emissions reduction and CDR will be needed to reach time flagged carbon neutrality targets after considering the adjustment in the terrestrial carbon sink.

Evaluation of eastern gamagrass as dual‐purpose complementary bioenergy and forage feedstock to switchgrass

AbstractSwitchgrass (SG) is considered a model bioenergy crop and a warm‐season perennial grass (WSPG) that traditionally served as forage feedstock in the United States. To avoid the sole dependence on SG for bioenergy production, evaluation of other crops to diversify the pool of feedstock is needed. We conducted a 3‐year field experiment evaluating eastern gamagrass (GG), another WSPG, as complementary feedstock to SG in one‐ and two‐cut systems, with or without intercropping with crimson clover or hairy vetch, and under different nitrogen (N) application rates. Our results showed that GG generally produced lower biomass (by 29.5%), theoretical ethanol potential (TEP, by 2.8%), and theoretical ethanol yield (TEY, by 32.9%) than corresponding SG under the same conditions. However, forage quality measures, namely acid detergent fiber (ADF), crude protein (CP), and elements P, K, Ca, and Mg were significantly higher in GG than those in SG. Nitrogen fertilizer significantly enhanced biomass (by 1.54 Mg ha−1), lignin content (by 2.10 g kg−1), and TEY (787.12 L ha−1) in the WSPGs compared to unfertilized treatments. Intercropping with crimson clover or hairy vetch did not significantly increase biomass of the WSPGs, or TEP and TEY in unfertilized plots. This study demonstrated that GG can serve as a complementary crop to SG and could be used as a dual‐purpose crop for bioenergy and forage feedstock in farmers' rotations.

Genetic determinants of switchgrass-root-associated microbiota in field sites spanning its natural range

A fundamental goal in plant microbiome research is to determine the relative impacts of host and environmental effects on root microbiota composition, particularly how host genotype impacts bacterial community composition. Most studies characterizing the effect of plant genotype on root microbiota undersample host genetic diversity and grow plants outside of their native ranges, making the associations between host and microbes difficult to interpret. Here, we characterized the root microbiota of a large diversity panel of switchgrass, a North American native C4 bioenergy crop, in three field locations spanning its native range. Our data, composed of 1,961 samples, suggest that field location is the primary determinant of microbiome composition; however, substantial heritable variation is widespread across bacterial taxa, especially those in the Sphingomonadaceae family. Despite diverse compositions, relatively few highly prevalent taxa make up the majority of the switchgrass root microbiota, a large fraction of which is shared across sites. Local genotypes preferentially recruit/filter for local microbes, supporting the idea of affinity between local plants and their microbiota. Using genome-wide association, we identified loci impacting the abundance of >400 microbial strains and found an enrichment of genes involved in immune responses, signaling pathways, and secondary metabolism. We found loci associated with over half of the core microbiota (i.e., microbes in >80% of samples), regardless of field location. Finally, we show a genetic relationship between a basal plant immunity pathway and relative abundances of root microbiota. This study brings us closer to harnessing and manipulating beneficial microbial associations via host genetics.