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Summary: Improving plant biomass yield and/or feedstock quality for highly efficient lignocellulose conversion has been the main research focus in genetic modification of switchgrass (Panicum virgatum L.), a dedicated model plant for biofuel production. Here, we proved that overexpression of miR396 (OE‐miR396) leads to reduced plant height and lignin content mainly by reducing G‐lignin monomer content. We identified nineteen PvGRFs in switchgrass and proved thirteen of them were cleaved by miR396. MiR396‐targeted PvGRF1, PvGRF9 and PvGRF3 showed significantly higher expression in stem. By separately overexpressing rPvGRF1, 3 and 9, in which synonymous mutations abolished the miR396 target sites, and suppression of PvGRF1/3/9 activity via PvGRF1/3/9‐SRDX overexpression in switchgrass, we confirmed PvGRF1 and PvGRF9 played positive roles in improving plant height and G‐lignin content. Overexpression of PvGRF9 was sufficient to complement the defective phenotype of OE‐miR396 plants. MiR396‐PvGRF9 modulates these traits partly by interfering GA and auxin biosynthesis and signalling transduction and cell wall lignin, glucose and xylan biosynthesis pathways. Moreover, by enzymatic hydrolysis analyses, we found that overexpression of rPvGRF9 significantly enhanced per plant sugar yield. Our results suggest that PvGRF9 can be utilized as a candidate molecular tool in modifying plant biomass yield and feedstock quality. [ABSTRACT FROM AUTHOR]

Abstract: Current knowledge of yield potential and best agronomic management practices for perennial bioenergy grasses is primarily derived from small‐scale and short‐term studies, yet these studies inform policy at the national scale. In an effort to learn more about how bioenergy grasses perform across multiple locations and years, the U.S. Department of Energy (US DOE)/Sun Grant Initiative Regional Feedstock Partnership was initiated in 2008. The objectives of the Feedstock Partnership were to (1) provide a wide range of information for feedstock selection (species choice) and management practice options for a variety of regions and (2) develop national maps of potential feedstock yield for each of the herbaceous species evaluated. The Feedstock Partnership expands our previous understanding of the bioenergy potential of switchgrass, Miscanthus, sorghum, energycane, and prairie mixtures on Conservation Reserve Program land by conducting long‐term, replicated trials of each species at diverse environments in the U.S. Trials were initiated between 2008 and 2010 and completed between 2012 and 2015 depending on species. Field‐scale plots were utilized for switchgrass and Conservation Reserve Program trials to use traditional agricultural machinery. This is important as we know that the smaller scale studies often overestimated yield potential of some of these species. Insufficient vegetative propagules of energycane and Miscanthus prohibited farm‐scale trials of these species. The Feedstock Partnership studies also confirmed that environmental differences across years and across sites had a large impact on biomass production. Nitrogen application had variable effects across feedstocks, but some nitrogen fertilizer generally had a positive effect. National yield potential maps were developed using PRISM‐ELM for each species in the Feedstock Partnership. This manuscript, with the accompanying supplemental data, will be useful in making decisions about feedstock selection as well as agronomic practices across a wide region of the country. [ABSTRACT FROM AUTHOR]

If the US mandates for the use of cellulosic biofuels are ultimately enforced, cellulosic feedstock will be demanded. Native switchgrass is a cellulosic feedstock that has been of substantial interest for this purpose because it is widely grown across the USA, it can be grown on marginal cropland and thus compete minimally with food supplies, it has a low carbon footprint, and in many ways, it is a sustainable source of energy. The purpose of the research reported here is to quantify the potential willingness of producers across 358 counties in a 10-state area in North Central USA to produce this biomass. We conducted a contingent valuation survey of randomly selected farm operators in this area. From the more than 1100 responses, we found that the mean reservation price at which respondents were willing to supply switchgrass from their least productive field is a return of about $228 per acre, which translates to about $82 per dry ton. Respondents were somewhat less willing to lease out their land for this purpose, requiring an additional $3.50 per dry ton to be willing to lease. In sub-regions of counties grouped by opportunity cost, mean reservation prices are equivalent to $75 per ton, $82 per ton, and $99 per ton, very close in the first two subregions to the Department of Energy goal of $84 per dry ton delivered to the biorefinery. Thus, prospects appear favorable that substantial fractions of farmers would be willing to supply switchgrass in this area, particularly in the sub-areas with lower land costs. © 2017 Society of Chemical Industry and John Wiley & Sons, Ltd [ABSTRACT FROM AUTHOR]

Switchgrass ( Panicum virgatum L.) is a C4 grass with high biomass yield potential and is now a model species for the Bioenergy Feedstock Development Program. Two distinct ecotypes (e.g., upland and lowland) and a range of plant morphotypes (e.g., leafy and stemmy) have been observed in switchgrass. The objective of this study was to determine the influence of ecotype and morphotype on biomass feedstock quality. Leaf and stem tissues of leafy and stemmy morphotypes from both lowland and upland ecotypes were analyzed for key feedstock traits. The leaf : stem ratio of leafy morphotype was more than 40% higher than the stemmy morphotype in both upland and lowland ecotypes. Therefore, the stemmy morphotype has significant advantages over leafy morphotype during harvesting, storage, transportation and finally the feedstock quality. Remarkable differences in feedstock quality and mineral composition were observed in switchgrass genotypes with distinct ecotypic origins and variable plant morphotypes. Lignin, hemicelluloses and cellulose concentrations were higher in stems than in the leaves, while ash content was notably high in leaves. A higher concentration of potassium was found in the stems compared to the leaves. In contrast, calcium was higher and magnesium was generally higher in the leaves compared to stems. The upland genotypes demonstrated considerably higher lignin (14.4%) compared with lowland genotypes (12.4%), while hemicellulose was higher in lowland compared with upland. The stemmy type demonstrated slightly higher lignin compared with leafy types ( P < 0.1). Differences between the ecotypes and morphotypes for key quality traits demonstrated the potential for improving feedstock composition of switchgrass through selection in breeding programs. [ABSTRACT FROM AUTHOR]

Biofuel crops may help achieve the goals of energy-efficient renewable ethanol production and greenhouse gas ( GHG) mitigation through carbon (C) storage. The objective of this study was to compare the aboveground biomass yields and soil organic C ( SOC) stocks under four crops (no-till corn, switchgrass, indiangrass, and willow) 7 years since establishment at three sites in Ohio to determine if high-yielding biofuel crops are also capable of high levels of C storage. Corn grain had the highest potential ethanol yields, with an average of more than 4100 L ha−1, and ethanol yields increased if both corn grain and stover were converted to biofuel, while willow had the lowest yields. The SOC concentration in soils under biofuels was generally unaffected by crop type; at one site, soil in the top 10 cm under willow contained nearly 13 Mg C ha−1 more SOC (or 29% more) than did soils under switchgrass or corn. Crop type affected SOC content of macroaggregates in the top 10 cm of soil, where macroaggregates in soil under corn had lower C, N and C : N ratios than those under perennial grasses or trees. Overall, the results suggest that no-till corn is capable of high ethanol yields and equivalent SOC stocks to 40 cm depth. Long-term monitoring and measurement of SOC stocks at depth are required to determine whether this trend remains. In addition, ecological, energy, and GHG assessments should be made to estimate the C footprint of each feedstock. [ABSTRACT FROM AUTHOR]

Before planting millions of hectares to switchgrass (Panicum virgatum L.) monocultures for producing biomass feedstock for biorefineries, it has been proposed that monocultures be tested against polycultures so, among other issues, the economics of both systems can be compared. This research was conducted to determine the lowest cost lignocellulosic biomass feedstock production system from among four monocultures and four polycultures. Randomized complete block designs with four replications were established at two Oklahoma locations. Plots were managed to represent anticipated production activities if perennial species were established in a low input system and harvested once a year to produce biorefinery feedstock. The four monocultures included switchgrass, sand bluestem (Andropogon hallii Hack.), Old World bluestem (OWB) (Bothriochloa ischaemum L. Keng), and big bluestem (A. gerardii Vitman). The four polycultures included mixtures of four grasses, four grasses and four forbs, eight grasses and eight forbs, and OWB with alfalfa (Medicago sativa L.). Plots were harvested once a year for 3 yr. For every treatment that included a mix of species, a dominant species emerged by the third harvest, suggesting that over time these treatments may not differ greatly from monocultures with minor representation of other species. The average yield was 4.6 Mg ha-1yr-1 for treat- ments seeded as monocultures at one location compared with 4.0 Mg ha-1yr-1 for the treatments seeded as polycultures. At the second location, monocultures averaged 7.9 Mg ha-1yr-1 and polycultures 6.5 Mg ha-1yr-1. Economics favored monocultures for the location and environmental conditions that occurred during the time period studied. [ABSTRACT FROM AUTHOR]

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

Biofuels from crops are emerging as a Jekyll & Hyde – promoted by some as a means to offset fossil fuel emissions, denigrated by others as lacking sustainability and taking land from food crops. It is frequently asserted that plants convert only 0.1% of solar energy into biomass, therefore requiring unacceptable amounts of land for production of fuel feedstocks. The C4 perennial grass Miscanthus× giganteus has proved a promising biomass crop in Europe, while switchgrass ( Panicum virgatum) has been tested at several locations in N. America. Here, replicated side-by-side trials of these two crops were established for the first time along a latitudinal gradient in Illinois. Over 3 years of trials, Miscanthus× giganteus achieved average annual conversion efficiencies into harvestable biomass of 1.0% (30 t ha−1) and a maximum of 2.0% (61 t ha−1), with minimal agricultural inputs. The regionally adapted switchgrass variety Cave-in-Rock achieved somewhat lower yields, averaging 10 t ha−1. Given that there has been little attempt to improve the agronomy and genetics of these grasses compared with the major grain crops, these efficiencies are the minimum of what may be achieved. At this 1.0% efficiency, 12 million hectares, or 9.3% of current US cropland, would be sufficient to provide 133 × 109 L of ethanol, enough to offset one-fifth of the current US gasoline use. In contrast, maize grain from the same area of land would only provide 49 × 109 L, while requiring much higher nitrogen and fossil energy inputs in its cultivation. [ABSTRACT FROM AUTHOR]