Emily A. Heaton

Miscanthus: A Promising Biomass Crop

The C4 grass Miscanthus × giganteus is of increasing interest as a biomass feedstock for renewable fuel production. This review describes what is known to date on M. × giganteus from extensive research in Europe and more recently in the US. Research trials have shown that M. × giganteus productivity is among the highest recorded within temperate climates. The crops high productivity results from greater levels of seasonal carbon fixation than other C4 crops during the growing season. Genetic sequencing of M. × giganteus has identified close homology with related crop species such as sorghum (Sorghum bicolor (L.) Moench) and sugarcane (Saccharum officinarum L.), and breeding of new varieties is underway. Miscanthus × giganteus has high water use efficiency; however, its exceptional productivity causes higher water use than other arable crops, potentially causing changes in hydrology in agricultural areas. Nitrogen use patterns are inconsistent and may indicate association with N fixing microorganisms. Miscanthus × giganteus has great promise as an economically and ecologically viable biomass crop; however, there are still challenges to widespread commercial development.

Seasonal nitrogen dynamics of Miscanthus×giganteus and Panicum virgatum

There is a tradeoff to consider when harvesting perennial biomass crops: harvest too late and yield declines, harvest too early and risk higher mineral contents, particularly nitrogen (N). Allowing the crop to completely senesce and recycle nutrients has several advantages, including improved feedstock quality and reduced fertilizer requirements, but it comes at a risk, particularly in temperate climates where snow and ice can reduce or destroy harvestable biomass. The effect of harvest time on the N concentration ([N]) and biomass of Panicum virgatum and Miscanthus×giganteus was evaluated at three sites in Illinois over two years. In both species [N] of standing biomass significantly declined with time (P<0.0001). Interestingly, there was no significant interaction effect of species and sample date on [N] (P=0.2888), but there was a highly significant interaction effect on the total N in standing biomass (P<0.0001). The amount of standing N was directly related to biomass yield. Seasonal changes in standing N differed among locations, suggesting that harvest time recommendations for N management depend on location. P. virgatum would have potentially removed as much as 187 kg N ha−1 if harvested green, and as little as 5 kg N ha−1 if harvested in late winter. Because of higher biomass yields, M. ×giganteus standing N ranged from 379 kg N ha−1 in June to <17 kg N ha−1 in February. Importantly, there was little overall change in [N] between an early winter (December) harvest and a late winter (February/March) harvest, indicating the benefits of N cycling in the system can be realized by end of the growing season and thus, at least from an N economy perspective, there is no reason to risk yield losses by delaying harvest over the winter.

Herbaceous energy crop development: recent progress and future prospects.

Oil prices and government mandates have catalyzed rapid growth of nonfossil transportation fuels in recent years, with a large focus on ethanol from energy crops, but the food crops used as first-generation energy crops today are not optimized for this purpose. We show that the theoretical efficiency of conversion of whole spectrum solar energy into biomass is 4.6-6%, depending on plant type, and the best year-long efficiencies realized are about 3%. The average leaf is as effective as the best PV solar cells in transducing solar energy to charge separation (ca. 37%). In photosynthesis, most of the energy that is lost is dissipated as heat during synthesis of biomass. Unlike photovoltaic (PV) cells this energetic cost supports the construction, maintenance, and replacement of the system, which is achieved autonomously as the plant grows and re-grows. Advances in plant genomics are being applied to plant breeding, thereby enabling rapid development of next-generation energy crops that capitalize on theoretical efficiencies while maintaining environmental and economic integrity.

Seasonal dynamics of above- and below-ground biomass and nitrogen partitioning in Miscanthus × giganteus and Panicum virgatum across three growing seasons

The first replicated productivity trials of the C4 perennial grass Miscanthus × giganteus in the United States showed this emerging ligno‐cellulosic bioenergy feedstock to provide remarkably high annual yields. This covered the 5 years after planting, leaving it uncertain if this high productivity could be maintained in the absence of N fertilization. An expected, but until now unsubstantiated, benefit of both species was investment in roots and perennating rhizomes. This study examines for years 5–7 yields, biomass, C and N in shoots, roots, and rhizomes. The mean peak shoot biomass for M. × giganteus in years 5–7 was 46.5 t ha−1 in October, declining to 38.1 t ha−1 on completion of senescence and at harvest in December, and 20.7 t ha−1 declining to 11.3 t ha−1 for Panicum virgatum. There was no evidence of decline in annual yield with age. Mean rhizome biomass was significantly higher in M. × giganteus at 21.5 t ha−1 compared to 7.2 t ha−1 for P. virgatum, whereas root biomass was similar at 5.6–5.9 t ha−1. M. × giganteus shoots contained 339 kg ha−1 N in August, declining to 193 kg ha−1 in December, compared to 168 and 58 kg ha−1 for P. virgatum. The results suggest substantial remobilization of N to roots and rhizomes, yet still a substantial loss with December harvests. The shoot and rhizome biomass increase of 33.6 t ha−1 during the 2‐month period between June and August for M. × giganteus corresponds to a solar energy conversion of 4.4% of solar energy into biomass, one of the highest recorded and confirming the remarkable productivity potential of this plant.

Does greater leaf-level photosynthesis explain the larger solar energy conversion efficiency of Miscanthus relative to switchgrass?

C(4) perennial grasses are being considered for bioenergy because of their high productivity and low inputs. In side-by-side replicated trials, Miscanthus (Miscanthus x giganteus) has previously been found more than twice as productive as switchgrass (Panicum virgatum). The hypothesis that this difference is attributable to higher leaf photosynthetic rates was tested on established plots of switchgrass and Miscanthus in central Illinois with >3300 individual measurements on 20 dates across the 2005 and 2006 growing seasons. Seasonally integrated leaf-level photosynthesis was 33% higher in Miscanthus than switchgrass (P < 0.0001). This increase in carbon assimilation comes at the expense of additional transpiration since stomatal conductance was on average 25% higher in Miscanthus (P < 0.0001). Whole-chain electron transport rate, measured simultaneously by modulated chlorophyll fluorescence, was similarly 23% higher in Miscanthus (P < 0.0001). Efficiencies of light energy transduction into whole chain photosynthetic electron transport, leaf nitrogen use and leaf water use were all significantly higher in Miscanthus. These may all contribute to its higher photosynthetic rates, and in turn, productivity. Systematic measurement of photosynthesis over two complete growing seasons in the field provides a unique dataset explaining why the productivity of these two species differs and for validating mechanistic production models for these emerging bioenergy crops.

Germination tests for assessing biochar quality.

Definition, analysis, and certification of biochar quality are crucial to the agronomic acceptance of biochar. While most biochars have a positive impact on plant growth, some may have adverse effects due to the presence of phytotoxic compounds. Conversely, some biochars may have the ability to adsorb and neutralize natural phytotoxic compounds found in soil. We evaluated the effects of biochars on seedling growth and absorption of allelochemicals present in corn ( L.) residues. Corn seeds were germinated in aqueous extracts of six biochars produced from varied feedstocks, thermochemical processes, and temperatures. Percent germination and shoot and radicle lengths were evaluated at the end of the germination period. Extracts from the six biochars had no effect on percent germination; however, extracts from three biochars produced at high conversion temperatures significantly inhibited shoot growth by an average of 16% relative to deionized (DI) water. Polycyclic aromatic hydrocarbons detected in the aqueous extracts are believed to be at least partly responsible for the reduction in seedling growth. Repeated leaching of biochars before extract preparation eliminated the negative effects on seedling growth. Biochars differ significantly in their capacity to adsorb allelochemicals present in corn residues. Germination of corn seeds in extracts of corn residue showed 94% suppression of radicle growth compared to those exposed to DI water; however, incubation of corn residue extracts with leached biochar for 24 h before initiating the germination test increased radicle length 6 to 12 times compared to the corn residue extract treatments. Germination tests appear to be a reliable procedure to differentiate between effects of different types of biochar on corn seedling growth.

Yields of Miscanthus × giganteus and Panicum virgatum decline with stand age in the Midwestern USA

For the C4 perennial grasses, Miscanthus × giganteus 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. virgatum over 8–10 years at seven locations across Illinois. The effect of stand age was determined by using a linear regression model that included effects of weather. Miscanthus × giganteus produced yields more than twice that of P. virgatum averaging 23.4 ± 1.2 Mg ha−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, suggesting a stronger effect of stand age on 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. These appear manageable numbers for the United States, given the 16.0 Mha in the farmland Conservation Reserve Program in addition to another 13.0 Mha abandoned from agriculture in the last decade.

Agronomic experiences with Miscanthus x giganteus in Illinois, USA.

Since 2002, researchers at the University of Illinois, Urbana-Champaign, Illinois, have been studying the perennial warm-season grass Miscanthus x giganteus (M. x g.) to determine its potential as a biomass feedstock. M. x g. originated in Japan and is a hybrid believed to have M. sinensis and M. sacchariflorus as its parents. Until recently, it was used as a landscape plant in the United States, but it is now the subject of research interest because of its potentially great biomass production. In central Illinois, M. x g. begins growth in April, typically reaches 2 m by the end of May, and is normally greater than 3 m by the end of September. The grass is sterile and propagated asexually using plantlets produced in tissue culture or by rhizome divisions. Following field planting, it generally takes at least three growing seasons to become fully established and reach optimal biomass production. In central Illinois, the senesced stems are harvested from early December through early March and can potentially be treated to produce ligno-cellulosic ethanol. In University of Illinois, research started in 2002. M. x g. produced an annual average of 22.0 t/ha in northern Illinois, 34.7 t/ha in central Illinois, and 35.4 t/ha in southern Illinois per year in 2004, 2005, and 2006.

SoyFACE: the Effects and Interactions of Elevated [CO2] and [O3] on Soybean

The SoyFACE experiment is the first to focus on the affects of e[CO2] and e[O3] on a seed legume under fully open-air conditions. The experiment mimicked e[CO2] and e[O3] predicted for the middle of this century and was conducted in one of the world’s major production areas for corn and soybean under cultivation and management techniques standard for the industry in the United States corn-belt region.Growth of soybean at e[CO2] resulted in an approximately 25 % increase in the daily integral of net leaf CO2 uptake, a 20% increase in the rate of light saturated CO2 uptake, a 15 % increase in seed yield, a 15 % increase in above ground primary productivity, and a 20 % increase in node number. Growth of soybean at e[CO2] also resulted in approximately a 30 % decrease in mid-day stomatal conductance, a 10 % decrease in stomatal conductance averaged over the day, an 8% decrease in the limitation of photosynthesis by stomatal conductance, and a 2–3 % decrease in harvest index.

Stem-Boring Caterpillars of Switchgrass in the Midwestern United States

ABSTRACT Lepidopteran stem borers were collected from switchgrass, Panicum virgatum L., tillers showing symptoms of infestation at seven locations in Illinois and Iowa, with additional observations made on larval and adult activity. Blastobasis repartella (Dietz) (Coleophoridae), whose only known host is switchgrass, was common in plots grown for >5 yr, whereas the polyphagous stalk borer, Papaipema nebris (Guenée) (Noctuidae), was abundant in newly established (i.e., first- and second-year) switchgrass. Haimbachia albescens Capps (Crambidae) was collected from two locations in Illinois, making switchgrass the first known host for this species. Entry holes made by B. repartella and H. albescens were usually 1–2 cm above the soil surface, precluding discrimination between these species based on external appearance of damage. Although P. nebris often entered stems within 5 cm of the soil surface, they also seemed to move between stems and were the only species entering stems at heights >15 cm. Adults of B. repartella were active on and above the switchgrass canopy by 2130 hours, with peak activity at ≈0230 hours. Activity of B. repartella adults seemed greatly reduced on one night with relatively cool temperatures and low wind speeds. Data from switchgrass and giant ragweed, Ambrosia trifida L., suggest P. nebris larvae move out of switchgrass during July in search of hosts with larger diameter stems, although by then hosts such as corn, Zea mays L., or Miscanthus spp. may have outgrown the potential for serious damage. However, switchgrass could contribute to greater adult populations of P. nebris if thick-stemmed hosts such as giant ragweed are not managed.