J. Ryan Stewart

Ecology and ecosystem impacts of common buckthorn ( Rhamnus cathartica ): a review

In this review, we synthesize the current knowledge of the ecology and impacts of Rhamnus cathartica L., a shrub from Europe and Asia that is a successful invader in North America. Physiological studies have uncovered traits including shade tolerance, rapid growth, high photosynthetic rates, a wide tolerance of moisture and drought, and an unusual phenology that may give R. cathartica an advantage in the environments it invades. Its high fecundity, bird-dispersed fruit, high germination rates, seedling success in disturbed conditions, and secondary metabolite production may also contribute to its ability to rapidly increase in abundance and impact ecosystems. R. cathartica impacts ecosystems through changes in soil N, elimination of the leaf litter layer, possible facilitation of earthworm invasions, unsubstantiated effects on native plants through allelopathy or competition, and effects on animals that may or may not be able to use it for food or habitat.

The ecology and agronomy of Miscanthus sinensis, a species important to bioenergy crop development, in its native range in Japan: a review.

Among several candidate perennial taxa, Miscanthus×giganteus has been evaluated and promoted as a promising bioenergy crop. Owing to several limitations, however, of the sterile hybrid, both at the taxon and agronomic production levels, other options need to be explored to not only improve M. ×giganteus, which was originally collected in Japan, but to also consider the development of other members of its genus, including Miscanthus sinensis, as bioenergy crops. Indeed, there is likely much to be learned and applied to Miscanthus as a bioenergy crop from the long history of intensive interaction between humans and M. sinensis in Japan, which in some regions of the country spans several thousand years. Combined with its high amount of genetic variation, stress tolerance, biotic interactions with fauna, and function as a keystone species in diverse grasslands and other ecosystems within its native range, the unique and extensive management of M. sinensis in Japan as a forage grass and building material provides agronomists, agroecologists, and plant breeders with the capability of better understanding this species in terms of potential contribution to bioenergy crop development. Moreover, the studies described in this review may serve as a platform for future research of Miscanthus as a bioenergy crop in other parts of the world.

Invasiveness potential of Miscanthus sinensis: implications for bioenergy production in the United States

Miscanthus sinensis (Anderss.) is a perennial grass species that has been grown widely as an ornamental since the late 1800s and is now being considered for bioenergy production in the United States. With its ability to be grown from seed and tolerate cold climates, this species offers practical advantages over current cultivars of the higher‐yielding hybrid species, M.×giganteus. Yet a large‐scale release of M. sinensis for bioenergy production in colder northern regions could result in new invasions into natural areas. We show, with reference to historical records and data collected in six wild US populations of M. sinensis in 2009, that ornamental varieties of this species have a long history of localized escape in the Eastern United States, primarily within the Appalachian region. To prevent further escape and gene flow, we recommend the development of sterile or functionally sterile varieties of M. sinensis or the restriction of its usage as a donor of genetic material to new sterile cultivars of M. ×giganteus. Other appropriate precautions for new biomass varieties include experimental demonstration of low invasiveness in the target region ahead of commercial production, along with postintroduction stewardship programs.

Discovery of natural Miscanthus (Poaceae) triploid plants in sympatric populations of Miscanthus sacchariflorus and Miscanthus sinensis in southern Japan

PREMISE OF THE STUDY Looming petroleum shortages and projected negative impacts of human-induced climate change may be partly alleviated by the development and use of bioenergy feedstock crops. Miscanthus ×giganteus, a highly productive sterile triploid hybrid grass that was discovered in Japan several decades ago, has considerable potential as an alternative source of energy. Given the risks, however, involved in the reliance upon production of one clone of this hybrid, which is a natural cross between Miscanthus sacchariflorus and Miscanthus sinensis, for lignocellulosic bioenergy production, natural occurrences of triploidy were investigated in sympatric populations of tetraploid M. sacchariflorus and diploid M. sinensis in Japan. METHODS Seeds were counted and DNA content was estimated by flow cytometry for plants of M. sacchariflorus and M. sinensis in several sympatric populations throughout Japan. Chromosomes were also counted for select plants. KEY RESULTS Based on seed-set data, M. sacchariflorus has significantly lower seed set than M. sinensis in Japan. Putative triploid seeds were found on M. sacchariflorus plants in southern Japan. CONCLUSIONS This is the first report of the natural occurrence of Miscanthus triploid plants in several decades. If found to be sterile and similar in productivity to the commonly cultivated clone of M. ×giganteus, these triploid plants might serve as additional sources of genetic variation for bioenergy production. Seed set data also indicates that other triploid plants might be found in more northern regions of Japan.

A roadmap for research on crassulacean acid metabolism (CAM) to enhance sustainable food and bioenergy production in a hotter, drier world

Crassulacean acid metabolism (CAM) is a specialized mode of photosynthesis that features nocturnal CO2 uptake, facilitates increased water-use efficiency (WUE), and enables CAM plants to inhabit water-limited environments such as semi-arid deserts or seasonally dry forests. Human population growth and global climate change now present challenges for agricultural production systems to increase food, feed, forage, fiber, and fuel production. One approach to meet these challenges is to increase reliance on CAM crops, such as Agave and Opuntia, for biomass production on semi-arid, abandoned, marginal, or degraded agricultural lands. Major research efforts are now underway to assess the productivity of CAM crop species and to harness the WUE of CAM by engineering this pathway into existing food, feed, and bioenergy crops. An improved understanding of CAM has potential for high returns on research investment. To exploit the potential of CAM crops and CAM bioengineering, it will be necessary to elucidate the evolution, genomic features, and regulatory mechanisms of CAM. Field trials and predictive models will be required to assess the productivity of CAM crops, while new synthetic biology approaches need to be developed for CAM engineering. Infrastructure will be needed for CAM model systems, field trials, mutant collections, and data management.

Genetic variation in Miscanthus × giganteus and the importance of estimating genetic distance thresholds for differentiating clones.

Miscanthus × giganteus (Mxg) is an important bioenergy feedstock crop, however, genetic diversity among legacy cultivars may be severely constrained. Only one introduction from Japan to Denmark of this sterile, triploid, vegetatively propagated crop was recorded in the 1930s. We sought to determine if the Mxg cultivars in North America were all synonyms, and if they were derived from the European introduction. We used 64 nuclear and five chloroplast simple sequence repeat (SSR) markers to estimate genetic similarity for 27 Mxg accessions from North America, and compared them with six accessions from Europe, including the species’ type‐specimen. A subset of accessions was also evaluated by restriction‐site associated DNA sequencing (RAD‐seq). In addition, we assessed the potential of new crosses to increase Mxg genetic diversity by comparing eight new triploid Mxg progeny grown from seed, along with samples of the parental species M. sacchariflorus and M. sinensis. Estimates of genotyping error rates were essential for distinguishing between experimental error and true genotypic differences among accessions. Given differences in estimated error rates and costs per marker for SSRs and RAD‐seq, the former is currently more cost‐effective for determining if two accessions are genetically identical. We concluded that all of the Mxg legacy cultivars were derived via vegetative propagation from a single genet. In contrast with the Mxg legacy cultivars, genetic similarity to the type‐specimen of eight new triploid Mxg progeny ranged from 0.46 to 0.56. Though genetic diversity among the Mxg legacy cultivars is critically low, new crosses can provide much‐needed variation to growers.

The Gene Pool of Miscanthus Species and Its Improvement

For more than a thousand years, people have used Miscanthus from wild stands or managed landscapes, to feed their livestock, roof their homes, make paper, dye possessions, and beautify their gardens. In recent decades there has been a call to develop Miscanthus into a fully domesticated biomass crop for sustainable renewable energy needs. Miscanthus is broadly distributed throughout eastern Asia and the Pacific islands, ranging from southern Siberia to tropical Polynesia, with a current center of diversity in temperate northern latitudes. Adaptation to cold and temperate environments is a distinctive feature of Miscanthus relative to other Saccharinae, facilitating its potential to become an important biomass crop in Europe and the USA. Auto- and allopolyploidy have played a role in the evolution of Miscanthus and polyploidy will likely be of central importance for the development and improvement of this crop. Variation for flowering time, including short-day flower induction, will permit plant breeders to optimize local adaptation and biomass-yield of Miscanthus, just as they have done for maize, sorghum and sugarcane. Germplasm collections that are representative of the genus and publicly available need to be established and characterized. Questions of taxonomy, origins, and evolution need attention from the research community. A multidisciplinary approach that includes population genetics, cytogenetics, molecular genetics, and genomics will be needed to rapidly increase our knowledge of the Miscanthus gene pool, which will facilitate the development of improved cultivars.

Empirical evidence of long-distance dispersal in Miscanthus sinensis and Miscanthus × giganteus

Abstract Many perennial bioenergy grasses have the potential to escape cultivation and invade natural areas. We quantify dispersal, a key component in invasion, for two bioenergy candidates:Miscanthus sinensis and M. × giganteus. For each species, approximately 1 × 106 caryopses dispersed anemochorously from a point source into traps placed in annuli near the source (0.5 to 5 m; 1.6 to 16.4 ft) and in arcs (10 to 400 m) in the prevailing wind direction. For both species, most caryopses (95% for M. sinensis and 77% for M. × giganteus) were captured within 50 m of the source, but a small percentage (0.2 to 3%) were captured at 300 m and 400 m. Using a maximum-likelihood approach, we evaluated the degree of support in our empirical dispersal data for competing functions to describe seed-dispersal kernels. Fat-tailed functions (lognormal, Weibull, and gamma (Γ)) fit dispersal patterns best for both species overall, but because M. sinensis dispersal distances were significantly affected by wind speed, curves were also fit separately for dispersal distances in low, moderate, and high wind events. Wind speeds shifted the M. sinensis dispersal curve from a thin-tailed exponential function at low speeds to fat-tailed lognormal functions at moderate and high wind speeds. M. sinensis caryopses traveled farther in higher wind speeds (low, 30 m; moderate, 150 m; high, 400 m). Our results demonstrate the ability of Miscanthus caryopses to travel long distances and raise important implications for potential escape and invasion of fertile Miscanthus varieties from bioenergy cultivation. Nomenclature: Eulaliagrass, Miscanthus sinensis Anderss.; giant miscanthus, Miscanthus × giganteus Anderss Interpretive Summary: Eulaliagrass (Miscanthus sinensis) has already escaped from ornamental plantings to form large naturalized populations hundreds of meters from original planting locations (Quinn et al. 2010). Our results suggest that these new populations could have established following long-distance seed dispersal. Because the potential for long-distance dispersal and subsequent establishment has been demonstrated, it is important to take preventive measures to avoid further propagule pressure and gene flow into naturalized populations. As has been pointed out, breeders of bioenergy and ornamental varieties can take steps to minimize the potential for escape by selecting for nonshattering seedheads, engineering glabrous seeds, and inducing sterility (Quinn et al. 2010). Our results indicate a strong effect of wind speed on dispersal distance in M. sinensis. Growers should be aware of the need to monitor for escaped plants, particularly if producing fertile varieties. Because we show that most giant miscanthus (Miscanthus × giganteus) and M. sinensis seeds were trapped near the source, exhaustive monitoring efforts should be conducted on a regular basis within 50 m of production fields. In addition, because we know that a small proportion of seeds can disperse several hundred meters from a source, growers should also coordinate efforts with local land managers to ensure early detection and control of escaped plants in nearby natural areas.

Genetic structure of Miscanthus sinensis and Miscanthus sacchariflorus in Japan indicates a gradient of bidirectional but asymmetric introgression

Summary Using high-density genetic markers, gene flow is identified from diploid Miscanthus sinensis to tetraploid M. sacchariflorus in Japan, in contrast to genetic isolation between these species in China.

Carbon budget and methane and nitrous oxide emissions over the growing season in a Miscanthus sinensis grassland in Tomakomai, Hokkaido, Japan

Species in the Miscanthus genus have been proposed as biofuel crops that have potential to mitigate elevated atmospheric carbon dioxide (CO2) levels and nitrous oxide (N2O) and methane (CH4) emissions. Miscanthus sinensis is widespread throughout Japan and has been used for biomass production for centuries. We assessed the carbon (C) budget and N2O and CH4 emissions over the growing season for 2 years in a M. sinensis‐dominated grassland that was naturally established around 1972 in Tomakomai, Hokkaido, Japan, which is near the northern limit for M. sinensis grassland establishment on Andisols. Average C budget was −0.31 Mg C ha−1, which indicates C was released from the grassland ecosystem to the atmosphere. Dominant components in the C budget appeared to be aboveground net primary production of plants (1.94–2.80 Mg C ha−1) and heterotrophic respiration (2.27–3.11 Mg C ha−1). The measurement of belowground net primary production (BNPP) of plants in the M. sinensis grassland was extremely variable, thus only an approximate value could be calculated. Mean C budget calculated with the approximated BNPP value was 1.47 and −0.23 Mg C ha−1 for 2008 and 2009, respectively. Given belowground biomass (9.46–9.86 Mg C ha−1) was 3.1–6.5 times higher than that of aboveground biomass may provide additional evidence suggesting this grassland represents a C sink. Average CH4 emissions across years of −1.34 kg C ha−1 would indicate this grassland acts as an atmospheric CH4 sink. Furthermore, average N2O emissions across years were 0.22 kg N ha−1. While the site may contribute N2O to the atmosphere, this value is lower compared with other grassland types. Global warming potential calculated with the approximated BNPP value was −5.40 and 0.95 Mg CO2 Eq ha−1 for 2008 and 2009, respectively, and indicates this grassland could contribute to mitigation of global warming.