Switchgrass Research Articles

Long–term rotational and perennial cropping benefit soil organic carbon stocks and ecosystem multifunctionality

Multipurpose cropping is promoted to provide biomass to meet the growing demand for biorefining, but excessive biomass removal may decrease soil C stocks and ecosystem multifunctionality. Here, soil C stocks across 0–200 cm depth and soil ecosystem multifunctionality at 0–40 cm were evaluated based on a 19–year field experiment, including three multipurpose cropping systems as continuous cotton (CC), ryegrass–sweet sorghum double cropping (RS) and perennial switchgrass (SG). Compared to CC, RS and SG increased the soil C stocks by 19% and 28%, and N stocks by 19% and 23% at 0–200 cm, respectively. The soil C stocks were positively correlated with belowground C input and negatively associated with C mineralization. RS and SG increased soil ecosystem multifunctionality by 16.8 and 15.7 folds at 0–20 cm and 0.34 and 0.61 folds at 20–40 cm relative to CC, respectively. The benefit of soil C stocks and ecosystem multifunctionality was more pronounced in SG than in RS due to the deeper root system. In conclusion, relative to continuous monoculture, rotational and perennial cropping can enhance soil C sequestration, maintain soil function, and provide feedstock for bioenergy.

Transcriptomic analysis of ncRNAs and mRNAs interactions during drought stress in switchgrass

Switchgrass (Panicum virgatum L.) plays a pivotal role as a bioenergy feedstock in the production of cellulosic ethanol and contributes significantly to enhancing ecological grasslands and soil quality. The utilization of non-coding RNAs (ncRNAs) has gained momentum in deciphering the intricate genetic responses to abiotic stress in various plant species. Nevertheless, the current research landscape lacks a comprehensive exploration of the responses of diverse ncRNAs, including long non-coding RNAs (lncRNAs), circular RNAs (circRNAs), and microRNAs (miRNAs), to drought stress in switchgrass. In this study, we employed whole transcriptome sequencing to comprehensively characterize the expression profiles of both mRNA and ncRNAs during episodes of drought stress in switchgrass. Our analysis identified a total of 12,511 mRNAs, 59 miRNAs, 38 circRNAs, and 368 lncRNAs that exhibited significant differential expression between normal and drought-treated switchgrass leaves. Notably, the majority of up-regulated mRNAs displayed pronounced enrichment within the starch and sucrose metabolism pathway, as validated through KEGG analysis. Co-expression analysis illuminated that differentially expressed (DE) lncRNAs conceivably regulated 1308 protein-coding genes in trans and 7110 protein-coding genes in cis. Furthermore, both cis- and trans-target mRNAs of DE lncRNAs exhibited enrichment in four common KEGG pathways. The intricate interplay between lncRNAs and circRNAs with miRNAs via miRNA response elements was explored within the competitive endogenous RNA (ceRNA) network framework. As a result, we constructed elaborate regulatory networks, including lncRNA-novel_miRNA480-mRNA, lncRNA-novel_miRNA304-mRNA, lncRNA/circRNA-novel_miRNA122-PvSS4, and lncRNA/circRNA-novel_miRNA14-PvSS4, and subsequently validated the functionality of the target gene, starch synthase 4 (PvSS4). Furthermore, through the overexpression of PvSS4, we ascertained its capacity to enhance drought tolerance in yeast. However, it is noteworthy that PvSS4 did not exhibit any discernible impact under salt stress conditions. These findings, as presented herein, not only contribute substantively to our understanding of ceRNA networks but also offer a basis for further investigations into their potential functions in response to drought stress in switchgrass.

Limiting acetoin generation during 2,3-butanediol fermentation with Paenibacillus polymyxa using lignocellulosic hydrolysates

Recent decarbonization efforts have led to interests in producing more bio-based chemicals. One attractive compound produced biochemically is the platform chemical known as 2,3-butanediol (2,3-BDO). In this work a mild alkaline pretreatment using sodium carbonate was performed on corn stover (CS) and switchgrass (SG) to generate hydrolysates for fermentation with the 2,3-BDO producer bacteria strain Paenibacillius polymyxa. Enzymatic hydrolysis performed on the pretreated CS and SG produced theoretical sugar yields of 80 % and 95 % for glucose and xylose, respectively. Fermentations with P. polymxya conducted in anaerobic bottles produced 2,3-BDO reaching concentrations ranging from 14 to 18 g/L with negligible conversion into acetoin. Bioreactor fermentations using the hydrolysate media generated up to 43 g/L and 34 g/L of 2,3-BDO from pretreated CS and SG, respectively, within 24 h of fermentation. However, 2,3-BDO product output was reduced by 40–50 % over the remainder of the fermentation due to conversion into acetoin caused by glucose depletion.

Comparison of vegetation composition in an ephemeral stream channel and the perimeter of pools in subtropical subhumid Central Texas

AbstractEphemeral streams are common in sub‐humid central Texas, but have received little attention. Within ephemeral streams are isolated pools that contain water for longer periods than the channel. This study examined the vegetation composition in an ephemeral dry stream channel and pools in Leon Creek. Twelve sites within the dry channel and twelve ephemeral pools in Leon Creek were surveyed for vegetation between late March and mid‐May 2020 in central Texas, USA. Plant species were similar between the dry channel and pools over a 1.5 km distance indicating that habitats are similar in both allowing the occurrence of upland, facultative, and wetland plant species. A total of 114 species of multiple functional groups were documented in this study. Panicum virgatum had greater coverage at >20% in both the ephemeral channel and pools compared to all other plant species. Ten plant species were dominant with a mean coverage of >3% and no difference was observed for dominant species in the dry channel and pools. The coverage of perennial species were significantly greater in the dry channel and pools but annual coverage in the dry channel was similar to perennial coverage in the pools. Graminoids and forbs were significantly greater in coverage compared to trees, shrubs, vines, and ferns in both the dry channel and pools. Shrub and tree cover was rare accounting for <0.3% coverage. Native species coverage was significantly greater compared to non‐native species in the dry channel and pools. Droughts, flash floods, and scouring events appear to promote perennial graminoids and forbs dominance in Leon Creek with shrubs and trees being uncommon. The results of this study is the first to evaluate vegetation in an ephemeral channel and pools in central Texas and provides current vegetation composition providing information that can be used to compare changes to vegetation in the future.

Metal mobility in an anaerobic-digestate-amended soil: the role of two bioenergy crop plants and their metal phytoremediation potential

Panicum virgatum and Pennisetum alopecuroides, two non-food bioenergy crops, were evaluated for their capacity to phyto-manage trace metals (Pb, Zn, Ni, Fe, Mn, Co, Cr, and Cu) from municipal solid waste digestate after its application to a marginal soil. For that, 90-day vertical soil column mesocosm (columns with 0.6 × 0.2 m) experiments were carried out to assess 1) the impact of digestate application on the health of marginal soil, 2) plant effect on digestate-borne trace metals’ mobility along the soil profile (measuring total metal levels and fractionation in different soil layers by atomic absorption spectroscopy, and 3) plant growth performance and trace metal (Pb, Zn, and Cu) uptake capacity. The results showed that trace metals were mostly confined in the 0–0.2 m soil horizon over the course of the experimental period, migrating from the digestate-amended soil layer (0–0.1 m) to the layer underneath (0.1–0.2 m) within the first 21 days and remaining stable afterward. No evidence of the trace metals’ mobility to deeper soil layers was detected. Migration of trace metals was reduced in the presence of P. virgatum and P. alopecuroides, suggesting a phytoremediation (phytostabilization) effect. For both plant species, no trace metal accumulation in the roots was observed (bioconcentration factor <1), although both plants showed a potential for Zn translocation for aboveground tissues (translocation factor >1). The growth of both plants was positively affected by municipal solid waste digestate application, which also improved soil quality (increased concentration of total organic carbon and available phosphorus, as well as cation exchange capacity and water holding capacity).

A Comparison of Dilute Aqueous Isethionic Acid and Sulfuric Acid in Hydrolysis of Three Different Untreated Lignocellulosic Biomass Varieties.

Efficient catalytic hydrolysis of lignocellulosic biomass to sugars is a major challenge in the production of sustainable biofuels and chemical feedstocks. In this study isethionic acid was compared with H2SO4 for hydrolysis of polysaccharides in corn stover, switch grass, and poplar. The catalytic activities of acids were compared by analysis of total reducing sugar (TRS) and glucose yields in a sequence of experiments in water at 90-190 °C using 0.050 mol of H+/L isethionic acid and H2SO4. In comparison to using H2SO4, the use of isethionic acid catalyst lowered the maximum TRS percent yield temperatures by 25, 24, and 21% for corn stover, switch grass, and poplar. A similar effect was observed for glucose percent yields as well. This temperature reduction is due to lowering of the activation energy in the polysaccharide depolymerization reaction and most likely due to hydrogen-bonding-type dipolar interactions between the isethionic acid -OH group and -OH groups in biomass polysaccharides.

Adaptability comparison and application assessment of various bioenergy grasses on different marginal lands in China

To understand the effects of different marginal land and environments on the growth, biomass yield, quality, and theoretical ethanol yield of different bioenergy grasses, and to compare the adaptability of different bioenergy grasses. This study was conducted in four representative marginal lands located in Chongqing, Liuyang, Nanyang, and Beijing. The agronomic traits, cell wall compositions, and theoretical alcohol yield of nine energy grasses containing 22 accessions were compared. The effects of environmental factors on biomass yield, quality, and theoretical ethanol yield of different accessions were evaluated via parametric and non-parametric statistics and AMMI analysis, and the stability and adaptability of all accessions were also compared. The results revealed that there were significant differences in biomass yield, quality, and theoretical alcohol yield among different species at the same trial site, and the same species also showed large differences between trial sites. Grasses exhibited divergent adaptability across trial sites, such as Saccharum arundinaceum and Miscanthus floridulus were sensitive to low temperatures and could not overwinter normally in Beijing. The biomass yield of Miscanthus sacchariflorus declined as the latitude decreased. Miscanthus × giganteus, Miscanthus lutarioriparius × sinensis, and Panicum virgatum exhibited greater resistance to environmental changes, indicating superior stability and environmental adaptability.

The effect of land-use conversion from agriculture to perennial biomass crops and nitrogen fertilizer on soil organic carbon stock in southern Ontario, Canada

Switchgrass [Panicum virgatum, (SG)] and miscanthus [Miscanthus spp., (Mis)] are perennial biomass crops (PBCs) commonly grown in Ontario, Canada. By the integration of PBCs on marginal/degraded agricultural (Ag) fields, a positive gain in soil organic carbon (SOC) sequestration has been reported in the scientific literature. Therefore, using PBCs to enhance SOC sequestration can potentially contribute to Canada's goal to reach net-zero greenhouse gas emissions by 2050. However, long-term field research (>10 years) to clearly demonstrate this trend in Canada is limited. In the above context, this study compared the current SOC stock (Mg C ha−1) in SG and Mis to that of baseline Ag SOC obtained from three different locations, namely Elora (2008–2019), Guelph (2009–2020) and Burlington (2016–2020), Ontario, Canada. SOC stock at the time of land-use conversion from Ag to SG and Mis was considered as baseline. Woodlots (WLs), undisturbed natural forests, were used as reference SOC (potential maximum SOC stock) to predict the potential SOC sequestration in the future by PBCs at the respective locations. Results showed that SOC stocks in all SG fields, Mis fields and WLs were higher compared to respective baseline Ag fields. SOC stocks (Mg C ha−1) in PBCs were significantly higher in Elora (SG: 96.3 ± 3.44, Mis: 100.0 ± 1.48) and Guelph (SG: 88.5 ± 5.72, Mis: 87.9 ± 6.43) over 11 years, whereas SOC stock in Burlington (SG: 87.5 ± 5.04, Mis: 94.7 ± 4.86), showed no significant difference over 4 years compared to their respective baseline Ag fields (77.6 ± 3.09, 59.3 ± 1.17 and 84.1 ± 3.39). All WLs had significantly higher SOC stock compared to their respective baseline Ag fields, showing the potential for future SOC stock gain by PBCs. SOC stock values in SG, with different nitrogen (N) fertilizer application rates (0, 40, 80 and 160 kg N ha−1), were not significantly different. Conversely, SOC stock at all N rates were significantly higher in SG than baseline Ag SOC stock values. For Mis, only N fertilizer rates 40, 80, 160 kg N ha−1 significantly increased SOC stock. However, within the four N fertilizer rates, SOC significantly increased only at 80 kg N ha−1. Increases in SOC stock suggest that converting marginal lands to PBCs over the long-term (>10 years) could create additional terrestrial C sinks. In Canada, there are close to 10 million ha of degraded Ag lands that can potentially be repurposed for PBCs, therefore the conversion of these unproductive Ag lands to PBCs could significantly contribute to Canada's climate mitigation strategies.

Proteobacterial dominance in endophytic bacterial diversity in switchgrass growing under nitrogen range and effect on plant growth

Switchgrass (Panicum virgatum L.) is native to North America and cultivated as a forage and bioenergy crop. Inorganic fertilizers enhance biomass production, increase production costs, and pollute the environment. Switchgrass cultivation using an eco-friendly approach might be achieved by inoculation with beneficial microbes. Therefore, the diversity of cultivable endophytic bacteria from roots and shoots of switchgrass growing under a nitrogen regime was studied. The potential of bacteria for plant growth promotion (PGP) was tested under in vitro conditions. A total of 216 bacterial isolates obtained belonged to four phyla and 33 genera, and most isolates were obtained from plants growing under no (0 kg/ha) or low nitrogen (90 kg/ha) input, rather than higher N (180 kg/ha). Higher numbers of isolates belonged to the phylum Proteobacteria, and genus-wise representation showed the dominance of Pseudomonas, Enterobacter, and rhizobia. Bacterial isolates were tested for PGP properties, e.g. phosphate solubilization, 1-aminocyclopropane-1-carboxylic acid (ACC) deaminase, Indole Acetic Acid (IAA) production, and nitrogen fixation. Many isolates were positive for one or more PGP properties. In in vitro analysis, selected bacterial isolates were inoculated in two commercial switchgrass cultivars and a showed cultivar-specific response. PGP isolates can be used for pot or field trials and eventually for the sustainable cultivation of switchgrass.

Assessment of plant ecological variability and heavy metal accumulation potential in naturally growing plant species of Pakhar bauxite mine site, Jharkhand, India

Abandoned bauxite mine (ABM) soil generally contains an unacceptable number of heavy metals (HMs), causing several ecological and environmental issues. The present study was conducted with a similar objective to assess the HM accumulation potential of the naturally growing plant species from Pakhar ABM site. Vegetation communities were studied using quadrat methods for plant species at both ABM and the control site (near the ABM site). A total of 21 (9 at the ABM site and 12 at the control site) plant species were recorded in the present study belonging to 10 families. Vegetation study revealed that the dominant plant species were Ammophila arenaria and Lantana camara at ABM site and Lantana camara at the control site. The concentration of HMs in soil at the ABM site, were 66180.00 mg kg−1 Al, 62.20 mg kg−1 Cr, 22.60 mg kg−1 Cu, 346800.00 mg kg−1 Fe, 780.80 mg kg−1 Mn, and 39.80 mg kg−1 Zn while in the soil of site located nearby taken as the control showed 56500.00 mg kg−1 Al, 4.40 mg kg−1 Cu, 51120.00 mg kg−1 Fe, 58.20 mg kg−1 Mn, 13.00 mg kg−1 Zn. Ammophila arenaria, Miscanthus sinensis, Acacia drepanolobium and Rumex pulcher exhibited the highest metal accumulation at the ABM site, while Ocimum campechianum, Lantana camara, Panicum virgatum L., Euphorbia hirta and Holcus lanatus, Cerastium glomeratum thuill and Shorea robusta exhibited the highest metal accumulation at control site. Plant Lantana camara showed considerable TF values for Pb, Al and Fe, from the ABM soil while Shorea robusta showed high TF values for Al, Cu, Zn, and Fe from the control soil. The BAF for Cu, Mn and Zn from ABM soil were observed in Acacia drepanolobium whereas Cerastium glomeratum thuill exhibited maximum BAF values for Zn and Cu from control soil.

Comparative analysis of switchgrass chloroplast genomes provides insights into identification, phylogenetic relationships and evolution of different ecotypes

Switchgrass (Panicum virgatum L.) plays a crucial role as a valuable forage and bioenergy resource. There are two ecotypes of switchgrass, upland and lowland, which exhibit significant differences in their adaptability to various environmental stressors. To enhance ecotype identification and gain a comprehensive understanding of the evolutionary relationships between these two ecotypes at the population level, we assembled 20 switchgrass chloroplast genomes (10 uplands and 10 lowlands) collected from different latitudinal regions. All chloroplast genomes displayed the typical quadripartite structure, with sizes ranging from 139,497 bp (J170. A) to 139,746 bp (J440. A and J636. B). The annotation of these 20 switchgrass chloroplast genomes revealed a consistent number of genes, including 40 transfer RNAs, eight ribosomal RNAs, and 86 protein-coding genes. Through multiscale analyses of the chloroplast genomes, we observed conservation in the upland and lowland chloroplasts in terms of IR boundaries, repetitive sequences, and codon usage. Our comparative chloroplast genome analysis revealed that large single copy regions exhibited the highest nucleotide diversity, followed by small single copy regions, while inverted repeat regions showed a relatively conserved pattern. Additionally, we identified a hotspot, trnG-GCC-trnM-CAU, which was exclusive to the lowland ecotype, suggesting its potential to differentiate between the two ecotypes. In the phylogenetic analysis, we found that some accessions from both ecotypes were intermixed and clustered into one clade, highlighting the complexity of the phylogenetic evolution process. In conclusion, we employed population-level comparative genomic analysis to investigate genetic variations and phylogenetic relationships among different ecotypes, thereby offering novel insights into the evolutionary dynamics and classifications of switchgrass.

Interactions among soil texture, pore structure, and labile carbon influence soil carbon gains

Perennial vegetation with high plant diversity, e.g., restored prairie, is known for stimulation of soil carbon (C) gains, due in part to enhanced formation of pore structure beneficial for long-term C storage. However, the prevalence of this phenomenon across soils of different types remains poorly understood. The aim of the study was to assess the associations between pore structure, soil C, and their differences in monoculture switchgrass and polyculture restored prairie vegetation across a wide range of soils dominating the Upper Midwest of the USA. Six experimental sites were sampled, representing three soil types with texture ranging from sandy to silt loams. The two vegetation systems studied at each site were (i) monoculture switchgrass (Panicum virgatum L.), and (ii) polyculture restored prairie, also containing switchgrass as one of its species. X-ray computed micro-tomography (µCT) was employed to analyze soil pore structure. Structural equation modeling and multiple path analyses were used to assess direct and indirect effects of soil texture and pore characteristics on microbial biomass C (MBC), particulate organic matter (POM), dissolved organic C (DOC), short-term respiration (CO2), and, ultimately, soil organic C (SOC). Across studied sites, prairie increased fractions of medium (50–150 µm Ø) pores by 11–45 %, SOC by 3–69 %, and MBC by 18–59 % (except for one site). The greater were the prairie-induced increases in the medium pore volumes, the greater were the prairie-induced SOC gains. Greater C losses via CO2 and DOC contributed to slower C accumulation in the prairie soil. We surmise that the interactive feedback loop relating medium pores and soil C acts across a wide range of soil textures and is an important mechanism through which perennial vegetation with high plant diversity, such as restored prairie, promotes rapid SOC gains.

Dynamic Reconfiguration of Switchgrass Proteomes in Response to Rust (Puccinia novopanici) Infection.

Switchgrass (Panicum virgatum L.) can be infected by the rust pathogen (Puccinia novopanici) and results in lowering biomass yields and quality. Label-free quantitative proteomics was conducted on leaf extracts harvested from non-infected and infected plants from a susceptible cultivar (Summer) at 7, 11, and 18 days after inoculation (DAI) to follow the progression of disease and evaluate any plant compensatory mechanisms to infection. Some pustules were evident at 7 DAI, and their numbers increased with time. However, fungal DNA loads did not appreciably change over the course of this experiment in the infected plants. In total, 3830 proteins were identified at 1% false discovery rate, with 3632 mapped to the switchgrass proteome and 198 proteins mapped to different Puccinia proteomes. Across all comparisons, 1825 differentially accumulated switchgrass proteins were identified and subjected to a STRING analysis using Arabidopsis (A. thaliana L.) orthologs to deduce switchgrass cellular pathways impacted by rust infection. Proteins associated with plastid functions and primary metabolism were diminished in infected Summer plants at all harvest dates, whereas proteins associated with immunity, chaperone functions, and phenylpropanoid biosynthesis were significantly enriched. At 18 DAI, 1105 and 151 proteins were significantly enriched or diminished, respectively. Many of the enriched proteins were associated with mitigation of cellular stress and defense.

Climate cooling benefits of cellulosic bioenergy crops from elevated albedo

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

High-efficiency utilization of biomass and seawater resources based on a distributed system with SOFC-assisted CO2 capture: Feasibility analysis and optimization

This paper develops a distributed system with SOFC-assisted carbon capture (SACC) by integrating the Rankine cycle, double-effect absorption chiller and multi-effect distillation unit to produce electricity, cooling and freshwater. To study the feasibility of the developed system, thermodynamic, economic and carbon footprint analyses and optimization are conducted on six different cases for the system. The results reveal that regardless of the biomass sources used as fuel, the developed SACC system requires 5%-9% less power consumption for CO2 capture compared to traditional methods. Moreover, the system fueled by switch grass exhibits superior efficiencies, and the system thermal efficiency (ηth) with SACC achieves 56.35% with corresponding levelized cost of products (cp) and total global warming potential (GWPt) of 54.94 $/GJ and −0.129 kg/kWh. Exergy analysis demonstrates that the prime mover unit (PMU) deserves the greatest irreversibility for all cases with a relative exergy destruction rate (y*k) of over 65% of the whole system. Within the PMU, the gasifier and SOFC are responsible for the highest irreversibility, and the y*k of the gasifier is over 50% and the SOFC’s is close to 9%. The parameter study indicates that an increase in the gasification temperature is unfavorable to ηth, however, it is conducive to the improvement of net power output (Wnet) when the temperature exceeds a certain value (e.g., 914.3℃ and 885.7℃ for Case-5 and Case-6). An appropriate increase in current density improves ηth and Wnet, and reduces cp, albeit slightly detrimental to environment. The optimization results demonstrate that Case-2 and Case-6 have superior thermodynamics and economics but are detrimental to the environment. In contrast, Case-1 and Case-5 are the most environmentally friendly, but their economics and thermodynamics are degraded to some extent.

Arbuscular mycorrhizal fungi enhance yield and photosynthesis of switchgrass (Panicum virgatum L.) under extreme drought and alters the biomass composition of the host plant

Drought is one of the major environmental stressors that affect plant growth and performance. To cope with such stresses most plants utilize belowground association with arbuscular mycorrhizal fungi (AMF). The AMF provide plants with nutrients and water in exchange for carbon fixed by their hosts. Very little is known about how this mutualism affect plant growth and physiology under extreme drought and in the context of lignocellulosic crops such as switchgrass. We investigated how AMF association affects switchgrass growth and physiology when under extreme drought (droughted to just above the permanent wilting point) in a factorial greenhouse experiment. This extreme drought was imposed at a level slightly above the permanent wilting point of switchgrass, which we measured. Although drought significantly depressed mycorrhizal colonization by ∼37%, the aboveground biomass in mycorrhizal plants increased by more than 3-fold under drought as compared to non-mycorrhizal plants. The increase in biomass was accompanied by a significant increase in net CO2 assimilation, stomatal conductance, and an enhanced intrinsic Water Use Efficiency. Drought increased aboveground lignin, starch, and sucrose by 9%, 151% and 16% respectively whereas AMF decreased total starch by 43%. Drought also decreased total cellulose by 10% as compared to the no-drought plants. AMF and drought also altered the composition of matrix polysaccharides. In this study, we found evidence that AMF are mostly beneficial to switchgrass under extreme drought and both the factors affect switchgrass biomass quality.

Tissue composition and higher heating values differ among six bioenergy grasses

Perennial crops are considered as one of the most promising substitutions for fossil fuels for both ethanol production and direct combustion, but the quality and suitability of bioenergy feedstock is species dependent. The bioenergy feedstock value of different perennial crops is mainly determined by tissue composition and higher heating value (HHV). A common garden field experiment with four replications was conducted to investigate differences in cellulose, hemicellulose, lignin, ash, and 14 different tissue elemental concentrations as well as HHV from tissues of switchgrass (Panicum virgatum L.), Miscanthus (Miscanthus×giganteus), indiangrass (Sorghastrum nutans), eastern gamagrass (Tripsacum dactyloides), reed canary grass (Phalaris arundinacea), and giant reed (Arundo donax L.) grown in 2020 and 2021 in Midwest USA. Results showed that Miscanthus, switchgrass, and indiangrass exhibited higher holocellulose (cellulose + hemicellulose) concentrations compared with eastern gamagrass, reed canary grass as well as giant reed: 684–687 g kg-1 vs 597–646 g kg-1 (2-yr averages). Switchgrass and Miscanthus had higher lignin concentrations (97–108 g kg-1) than the other four species (66–84 g kg-1). Greater 2-yr averaged HHVs were observed in switchgrass (18.1 MJ kg-1) and Miscanthus (17.8 MJ kg-1) than for giant reed (17.3 MJ kg-1), eastern gamagrass (17.0 MJ kg-1), indiangrass (16.9 MJ kg-1), and reed canary grass (16.5 MJ kg-1), which was correlated with differences in ash concentration between switchgrass and Miscanthus (25–29 g kg-1) and the other four species (42–91 g kg-1). Switchgrass, Miscanthus, and indiangrass exhibited significantly lower nitrogen, sulfur, and potassium concentrations than the other grass species, which would lead to less NOx and SOx emission, and sintering or slag formation in the combustion chamber. Giant reed obtained the greatest potential ethanol and combustion yields on a single plant basis, followed by Miscanthus, switchgrass, indiangrass, eastern gamagrass, and reed canary grass; however, further studies are needed to evaluate biomass yields on an area basis.

A 30% reduction in switchgrass rhizome reserves did not decrease biomass yield

AbstractA long‐standing question in perennial grass breeding and physiology is whether yield improvement strategies could compromise winter survival. Since perennial grasses rely on stored carbohydrates for winter maintenance and spring regrowth, yield improvement strategies could reduce winter survival if they increase biomass and grain yields at the expense of carbon allocation to storage. Therefore, it is crucial to comprehend the dependence of regrowth on storage reserves. We experimentally depleted switchgrass (Panicum virgatum L.) rhizome reserves by storing rhizomes for 2 weeks at 5°C (control treatment) and 25°C (reserve‐depleted treatment). During the storage period rhizome respiration was 5.3× higher at 25°C (0.010 μmol CO2 g−1 min−1 at 5°C vs. 0.054 μmol CO2 g−1 min−1 at 25°C; p < 0.0001) and the starch content was depleted by 30% by the end of storage. Surprisingly, reserve‐depleted switchgrass had 60% larger leaf area (LA; LAcontrol = 149 cm2 pot−1 vs. LAdepleted = 239 cm2 pot−1; p = 0.013) and produced ~40% more aboveground biomass than control plants (9.46 g pot−1 vs. 6.63 g pot−1; p = 0.112). In addition, reserve‐depleted switchgrass restored its rhizome starch reserves to pre‐storage levels. Switchgrass showed a large plasticity among its source‐sink components to buffer the imposed reserve depletion. It increased plant photosynthesis by increasing the photosynthetic leaf area while keeping photosynthesis constant on a leaf area basis and readjusted the timing and activity of sink organs. These results suggest that switchgrass, and potentially other perennial grasses, largely over‐invest in storage reserves. Therefore, current breeding strategies in perennial grasses aimed to extend the aboveground growing season should not compromise crop persistence. Our study also has implications on long‐term yield dynamics as it highlights sink limitations as potential driver of the yield decline commonly observed in perennial grasses 5+ years after cultivation.

Long‐term changes in soil carbon and nitrogen fractions in switchgrass, native grasses, and no‐till corn bioenergy production systems

AbstractCellulosic bioenergy is a primary land‐based climate mitigation strategy, with soil carbon (C) storage and nitrogen (N) conservation as important mitigation elements. Here, we present 13 years of soil C and N change under three cellulosic cropping systems: monoculture switchgrass (Panicum virgatum L.), a five native grasses polyculture, and no‐till corn (Zea mays L.). Soil C and N fractions were measured four times over 12 years. Bulk soil C in the 0–25 cm depth at the end of the study period ranged from 28.4 (± 1.4 se) Mg C ha−1 in no‐till corn, to 30.8 (± 1.4) Mg C ha−1 in switchgrass, and to 34.8 (± 1.4) Mg C ha−1 in native grasses. Mineral‐associated organic matter (MAOM) ranged from 60% to 90% and particulate organic matter (POM) from 10% to 40% of total soil C. Over 12 years, total C as well as both C fractions persisted under no‐till corn and switchgrass and increased under native grasses. In contrast, POM N stocks decreased 33% to 45% across systems, whereas MAOM N decreased only in no‐till corn and by less than 13%. Declining POM N stocks likely reflect pre‐establishment land use, which included alfalfa and manure in earlier rotations. Root production and large soil aggregate formation explained 69% (p < 0.001) and 36% (p = 0.024) of total soil C change, respectively, and 60% (p = 0.020) and 41% (p = 0.023) of soil N change, demonstrating the importance of belowground productivity and soil aggregates for producing and protecting soil C and conserving soil N. Differences between switchgrass and native grasses also indicate a dependence on plant diversity. Soil C and N benefits of bioenergy crops depend strongly on root productivity and pre‐establishment land use.

Seed yield and quality of switchgrass formed in different plant tiers

Purpose. To establish the features of yield formation and seed quality in switchgrass (Panicum virgatum L.) depending on its location on the plant – panicles of the 1st and 2nd tiers. Methods. Laboratory, measuring and weighing, mathematical and statistical. Results. There was no significant difference in the yield of cleaned seeds depending on the place of their formation. On average over four years, the yield of seeds from panicles of the first tier was 91.9% and from the second tier 90.6%. It was found out that in the Central Forest Steppe of Ukraine, the yield of switchgrass seeds significantly depended on both the growing conditions (year) and the panicle tier. On average over the years of research, significantly higher seed yield was formed on the panicle of the first tier of both varieties. It was 0.83 g on the panicle of the first tier in variety 'Cave-in-Rock' and 0.70 g in 'Sunburst'. On the panicle of the second tier, the productivity was significantly lower − by 0.35 and 0.31 g, respectively (LSD0.05 tier = 0.24), and was 0.48 g and 0.39 g per panicle. Any significant difference based on varietal characteristics was not detected. The biggest influence on seed yield made cultivation conditions of the year (47.7%) followed by panicle layer (32.9%). The influence of other factors and their interaction was insignificant. The quality of the seed depended both on varietal characteristics and on the place of its formation on the plants. On average, over four years, the seed quality indicators - germination energy and germination – from panicles of the first tier were significantly higher in ‘Cave-in-Rock’, amounting 33% and 34%, respectively. In the second tier, on the contrary, the indicators were higher in ‘Sunburst’ and amounted to 35% (LSD0.05 variety = 0.3%). Conclusions. The yield and quality of switchgrass seeds was significantly affected by cultivation conditions of the year, varietal characteristics and the place of grain formation. The highest yield was formed on the panicle of the first tier in both varieties. 'Cave-in-Rock' formed significantly higher seed yield on the panicles of all tiers, compared to 'Sunburst'. A significantly higher seed germination and germination energy was obtained with the seeds harvested from the panicles of the first tier.