Dihaploid Stocks of Switchgrass Isolated by a Screening Approach

Manipulation of ploidy in switchgrass has potential to accelerate inbred production and to provide insight about genome structure through either sequencing or cytogenetic approaches. We have identified two dihaploid individuals isolated from among the progeny of a controlled cross between two individuals of the cultivars Alamo and Kanlow. The dihaploid lines were initially distinguished from the parental lines by their reduced heterozygosity and were subsequently confirmed through estimation of C values by flow cytometry and chromosome counts of metaphase root tip squash preparations. These plants are functionally sterile, with floral bracts that remain closed and inviable pollen. They can be easily distinguished from tetraploid individuals by their reduced stature, smaller epidermal cell size, and lower number of chloroplasts per guard cell. Aberrant meiosis in these individuals is evidenced by a lack of regular pairing at diakinesis and metaphase I and suggests that the non-homologous genomes are distinct from one another. The reduced genome size of these dihaploids will facilitate basic genome studies and genetic analyses that are impossible or problematic in polyploid accessions.     

Nitrogen-Use Dynamics in Switchgrass Grown for Biomass

This work examines N use by switchgrass (Panicum virgatum L.). A study was conducted on two well-established ‘Cave-in-Rock’ switchgrass stands in Blacksburg (37° 11′ N, 80° 25′ W) and Orange (38° 13′ N, 78° 07′ W) Virginia, USA. Plots were fertilized in 2001 (year 1) with 0, 90, 180, or 270 kg N per hectare. No additional N was applied in 2002 (year 2) and 2003 (year 3), and biomass was harvested in July and November for years 2 and 3 (but only in November of year 1). Root and soil samples were collected in May, July, September, and November each year and analyzed for N. Nitrogen fertilization did not increase yields in 2001 (year 1), but it did provide residual benefits in 2002 (year 2) and 2003 (year 3). Root-N levels at 15 cm depth increased with fertilization, fluctuated seasonally between roots and shoots, and root-N was reduced over the course of the study. With two harvests per year, about 100 kg N hectare per year were removed in biomass, even in plots with no N added—suggesting N already present in the soils (at 15 cm depth) contributed to yields; but the soil mineral-N pools were reduced by the end of year 3. Nitrogen-use efficiency, apparent N recovery, and partial factor productivity were reduced with higher N applications. The data support the notion that biomass production can be achieved with minimal N inputs, but stands must be managed to maintain that N reserve over the long term. There is also a need to quantify the N pool to depths greater than 15 cm in other agro-ecoregions.     

Identification of a Selfing Compatible Genotype and Mode of Inheritance in Switchgrass

Switchgrass (Panicum virgatum L.) is being targeted for use as a dedicated lignocellulosic feedstock crop for producing bioenergy in the United States. The breeding of new switchgrass cultivars with enhanced performance is a research emphasis supporting the targeted use. The species is considered allogamous due to wind facilitated cross-pollination and strong genetic self-incompatibility. Plants typically produce few or no seed when self-fertilized. No attempt has been made to identify selfing-compatible plants that would potentially enable developing inbred lines. Here, using a set of 12 simple sequence repeat-based molecular markers, we identified one lowland plant, ??NL94 LYE 16?×?13?? (NL94), demonstrating high self-compatibility. A large potted plant of NL94 and a similar size plant of ??SL93 7?×?15?? were grown in a growth chamber for the purpose of producing a hybrid full-sib mapping population. Marker analyses of 456 progeny from the NL94 plant indicated that 279 (61.2%) and 177 (38.8%) resulted from self- and cross-fertilization, respectively. SSR marker segregation analyses in both the selfed and hybrid progeny populations conclusively indicated disomic inheritance in the two switchgrass parents. Disomic inheritance of switchgrass is significant to the development of switchgrass inbreds as homozygosity is approached much faster via inbreeding under disomic vs. tetrasomic inheritance. Self-compatibility in switchgrass potentially enables the development of inbred lines for use in producing heterotic F1 hybrid cultivars.     

Switchgrass Harvest Progression in the North-Central USA

In the North-Central USA, switchgrass to be used as a biomass feedstock typically will be harvested in the autumn. The accumulated area harvested over the harvest season (defined here as the harvest progression) will influence the size of the machinery fleet and seasonal labor required to complete the majority of the harvest before the first lasting snow. A harvest progression model was developed that uses drying rate, mower and baler productivity, and weather conditions as major inputs. Ten years of weather data (2005–2014) from Wisconsin, Iowa, and Nebraska (WI, IA, NE) were used. Harvest progression was modeled for four harvest systems involving conventional and intensive conditioning both swathed and tedded (CC, IC, CCT, and ICT, respectively) and two dates at which harvest began (1 September and after a killing frost). To reduce risk of exposing crop to prolonged periods of inclement weather, mowers were idled when more than 80 ha were cut but not yet baled. For all sites, the harvest start date and the mower idled constraint had greater impact on harvest progression than the type of harvest system. Harvest progression was greatest when mowing started on 1 September and continued whenever weather permitted (i.e., no mower idled constraint). Compared to the harvest system used today (CC), using the IC system resulted in more area harvested with less crop exposed to rain after cutting and considerably less area left to be baled in the spring. Starting harvest on 1 September, using intensive conditioning, and not idling the mowers might be considered the system that best balances the desire for rapid harvest progression, small equipment fleet size, low-capital expenditures, and maximum labor utilization.     

Transcriptional Analysis of Flowering Time in Switchgrass

Over the past two decades, switchgrass (Panicum virgatum) has emerged as a priority biofuel feedstock. The bulk of switchgrass biomass is in the vegetative portion of the plant; therefore, increasing the length of vegetative growth will lead to an increase in overall biomass yield. The goal of this study was to gain insight into the control of flowering time in switchgrass that would assist in development of cultivars with longer vegetative phases through delayed flowering. RNA sequencing was used to assess genome-wide expression profiles across a developmental series between switchgrass genotypes belonging to the two main ecotypes: upland, typically early flowering, and lowland, typically late flowering. Leaf blades and tissues enriched for the shoot apical meristem (SAM) were collected in a developmental series from emergence through anthesis for RNA extraction. RNA from samples that flanked the SAM transition stage was sequenced for expression analyses. The analyses revealed differential expression patterns between early- and late-flowering genotypes for known flowering time orthologs. Namely, genes shown to play roles in photoperiod response and the circadian clock in other species were identified as potential candidates for regulating flowering time in the switchgrass genotypes analyzed. Based on their expression patterns, many of the differentially expressed genes could also be classified as putative promoters or repressors of flowering. The candidate genes presented here may be used to guide switchgrass improvement through marker-assisted breeding and/or transgenic or gene editing approaches.     

Switchgrass for bioethanol and other value-added applications: a review

Switchgrass is a promising feedstock for value-added applications due to its high productivity, potentially low requirements for agricultural inputs and positive environmental impacts. The objective of this paper is to review published research on the conversion of switchgrass into bioethanol and other value-added products. Environmental benefits associated with switchgrass include the potential for carbon sequestration, nutrient recovery from runoff, soil remediation and provision of habitats for grassland birds. Pretreatment of switchgrass is required to improve the yields of fermentable sugars. Based on the type of pretreatment, glucose yields range from 70% to 90% and xylose yields range from 70% to 100% after hydrolysis. Following pretreatment and hydrolysis, ethanol yields range from 72% to 92% of the theoretical maximum. Other value-added uses of switchgrass include gasification, bio-oil production, newsprint production and fiber reinforcement in thermoplastic composites. Future prospects for research include increased biomass yields, optimization of feedstock composition for bioenergy applications, and efficient pentose fermentation to improve ethanol yields.     

Proteogenomic Analysis of a Thermophilic Bacterial Consortium Adapted to Deconstruct Switchgrass

Thermophilic bacteria are a potential source of enzymes for the deconstruction of lignocellulosic biomass. However, the complement of proteins used to deconstruct biomass and the specific roles of different microbial groups in thermophilic biomass deconstruction are not well-explored. Here we report on the metagenomic and proteogenomic analyses of a compost-derived bacterial consortium adapted to switchgrass at elevated temperature with high levels of glycoside hydrolase activities. Near-complete genomes were reconstructed for the most abundant populations, which included composite genomes for populations closely related to sequenced strains of Thermus thermophilus and Rhodothermus marinus, and for novel populations that are related to thermophilic Paenibacilli and an uncultivated subdivision of the little-studied Gemmatimonadetes phylum. Partial genomes were also reconstructed for a number of lower abundance thermophilic Chloroflexi populations. Identification of genes for lignocellulose processing and metabolic reconstructions suggested Rhodothermus, Paenibacillus and Gemmatimonadetes as key groups for deconstructing biomass, and Thermus as a group that may primarily metabolize low molecular weight compounds. Mass spectrometry-based proteomic analysis of the consortium was used to identify >3000 proteins in fractionated samples from the cultures, and confirmed the importance of Paenibacillus and Gemmatimonadetes to biomass deconstruction. These studies also indicate that there are unexplored proteins with important roles in bacterial lignocellulose deconstruction.     

Seasonal variability in net ecosystem carbon dioxide exchange over a young Switchgrass stand

Understanding carbon dynamics of switchgrass ecosystems is crucial as switchgrass (Panicum virgatum L.) acreage is expanding for cellulosic biofuels. We used eddy covariance system and examined seasonal changes in net ecosystem CO₂ exchange (NEE) and its components – gross ecosystem photosynthesis (GEP) and ecosystem respiration (ER) – in response to controlling factors during the second (2011) and third (2012) years of stand establishment in the southern Great Plains of the United States (Chickasha, OK). Larger vapor pressure deficit (VPD > 3 kPa) limited photosynthesis and caused asymmetrical diurnal NEE cycles (substantially higher NEE in the morning hours than in the afternoon at equal light levels). Consequently, rectangular hyperbolic light–response curve (NEE partitioning algorithm) consistently failed to provide good fits at high VPD. Modified rectangular hyperbolic light–VPD response model accounted for the limitation of VPD on photosynthesis and improved the model performance significantly. The maximum monthly average NEE reached up to ?33.02 ± 1.96 μmol CO₂ m^?2 s^?1 and the highest daily integrated NEE was ?35.89 g CO₂ m^?2 during peak growth. Although large differences in cumulative seasonal GEP and ER were observed between two seasons, total seasonal ER accounted for about 75% of GEP regardless of the growing season lengths and differences in aboveground biomass production. It suggests that net ecosystem carbon uptake increases with increasing GEP. The ecosystem was a net sink of CO₂ during 5–6 months and total seasonal uptakes were ?1128 ± 130 and ?1796 ± 217 g CO₂ m^?2 in 2011 and 2012, respectively. In conclusion, our findings suggest that the annual carbon status of a switchgrass ecosystem can be a small sink to small source in this region if carbon loss from biomass harvesting is considered. However, year‐round measurements over several years are required to assess a long‐term source‐sink status of the ecosystem.     

A Genomics Approach to Deciphering Lignin Biosynthesis in Switchgrass

It is necessary to overcome recalcitrance of the biomass to saccharification (sugar release) to make switchgrass (Panicum virgatum) economically viable as a feedstock for liquid biofuels. Lignin content correlates negatively with sugar release efficiency in switchgrass, but selecting the right gene candidates for engineering lignin biosynthesis in this tetraploid outcrossing species is not straightforward. To assist this endeavor, we have used an inducible switchgrass cell suspension system for studying lignin biosynthesis in response to exogenous brassinolide. By applying a combination of protein sequence phylogeny with whole-genome microarray analyses of induced cell cultures and developing stem internode sections, we have generated a list of candidate monolignol biosynthetic genes for switchgrass. Several genes that were strongly supported through our bioinformatics analysis as involved in lignin biosynthesis were confirmed by gene silencing studies, in which lignin levels were reduced as a result of targeting a single gene. However, candidate genes encoding enzymes involved in the early steps of the currently accepted monolignol biosynthesis pathway in dicots may have functionally redundant paralogues in switchgrass and therefore require further evaluation. This work provides a blueprint and resources for the systematic genome-wide study of the monolignol pathway in switchgrass, as well as other C4 monocot species.     

Simple Experimental Methods for Determining the Apparent Focal Shift in a Microscope System

Three-dimensional optical microscopy is often complicated by a refractive index mismatch between the sample and objective lens. This mismatch causes focal shift, a difference between sample motion and focal-plane motion, that hinders the accuracy of 3D reconstructions. We present two methods for measuring focal shift using fluorescent beads of different sizes and ring-stained fluorescent beads. These simple methods are applicable to most situations, including total internal reflection objectives and samples very close to the interface. For distances 0–1.5 μm into an aqueous environment, our 1.49-NA objective has a relative focal shift of 0.57 ± 0.02, significantly smaller than the simple n ₂/n ₁ approximation of 0.88. We also expand on a previous sub-critical angle theory by means of a simple polynomial extrapolation. We test the validity of this extrapolation by measuring the apparent focal shift in samples where the refractive index is between 1.33 and 1.45 and with objectives with numerical apertures between 1.25 and 1.49.     

Genetic Diversity in Switchgrass Collections Assessed by EST-SSR Markers

Switchgrass (Panicum virgatum L.), is a warm season C₄ perennial grass, native to North American tall grass prairies. The high biomass production potential of switchgrass with low inputs makes it an excellent choice as a sustainable bioenergy crop. The objective of this study was to determine the genetic variability within and among 31 switchgrass populations obtained from Germplasm Resources Information Network (GRIN). Six plants from each population (186 genotypes) were characterized with 24 conserved grass expressed sequence tag-simple sequence repeats (EST-SSR) and 39 switchgrass EST-SSR markers. The partitioning of variance components based on the analysis of molecular variance (AMOVA) revealed that the variability within population was significantly higher (80%) than among populations (20%). Pair-wise genetic distance estimates based on SSR data revealed dissimilarity coefficients for genotypes ranging from 0.45 to 0.81. The uplands and lowlands were generally grouped in distinct sub-clusters. The genotypes were grouped into the different adaptive zones based on the geographical locations of the collections. Ploidy estimation showed that 20 of the accessions were tetraploid, four of them were octoploids and the remaining seven had mixed ploidy levels. Flow cytometry analysis of genotypes within cultivars collected from commercial seed sources did not always support the ploidy mixtures that were found in GRIN collections. Three genotypes of two accessions that clustered differently from other genotypes of the same accessions also had different ploidy levels.     

Searching for a Role of Nursing Personnel in Developing Landscape of Ehealth: Factors Determining Attitudes toward Key Patient Empowering Applications

IntroductionNurses may play an important role in the delivery of medical services based on the use of ehealth tools. Nevertheless, their taking an active role in an ehealth environment depends on their possessing the appropriate skills and mindset. The main objective of this paper was to assess nurses’ opinions and to analyze the predictors of their acceptance of ehealth features relevant to patient empowerment with a strong focus on chronic care.MethodsA survey was conducted among nurses from hospital centers of south-eastern Poland based on a questionnaire designed to assess their attitudes toward the ehealth domain. The predictors of the nurses’ acceptance of ehealth usage within specific contexts were assessed with uni- and multivariate logistic regression.ResultsAn analysis was performed on data from 648 questionnaires retained after a quality check. The duration of Internet use was consistently related to higher acceptance of ehealth applications and more certainty regarding the reliability of health-related information available on the Internet. Nurses from urban medical centers were more skeptical about the use of specific ehealth solutions.ConclusionPrevious experience in using information technologies is the main factor influencing the acceptance of specific ehealth solutions relevant for care provided to patients suffering from chronic conditions.     

Photoshop在园林设计后期处理中的运用

介绍了Photoshop在园林设计中的应用,对平面图进行后期处理中的操作步骤进行一定的探讨。     

Natural Variation for Nutrient Use and Remobilization Efficiencies in Switchgrass

Nutrient management in biomass production systems serves to maximize yield and minimize production costs and environmental impact. Loss of soil nutrients with harvested biomass can be reduced by the judicious choice of genotype and harvest time. Sustainable production of switchgrass for biofuel will depend, in part, on breeding of varieties that are conservative in their use of soil nutrients to produce biomass. To aid such breeding programs, we assessed the natural variation in nutrient-use and remobilization efficiencies of 31 accessions of Panicum virgatum by measuring the concentration of 20 elements (N, P, K, Li, B, Na, Mg, Ca, Mn, Fe, Co, Ni, Cu, Zn, As, Se, Rb, Sr, Mo, and Cd) in shoots of field-grown plants harvested at two different stages of development. Significant differences between accessions were found for elemental composition at maturity and after senescence. The concentration of several elements (N, P, K, and Rb) decreased in the shoots of all accessions during senescence, although the efficiency of remobilization ranged from 20% to 61% for N, 31% to 65% for P, 25% for 84% for K, and 33% to 84% for Rb. The accessions/cultivars with the greatest nutrient-use efficiency (smallest loss of nutrient per unit biomass) were BN-14668-65, Kanlow, Caddo from the point of view of N content, and Kanlow, Cave-in-Rock, and Blackwell from the point of view of P content in senescent shoots. Finally, differences in elemental composition between upland and lowland ecotypes were also found. The information presented here will help to guide future breeding programs and nutrient management practices.     

An Improved Tissue Culture System for Embryogenic Callus Production and Plant Regeneration in Switchgrass (Panicum virgatum L.)

The increased emphasis on research of dedicated biomass and biofuel crops begs for biotechnology method improvements. For switchgrass (Panicum virgatum L.), one limitation is inefficient tissue culture and transformation systems. The objectives of this study were to investigate the utility of a new medium described here, LP9, for the production and maintenance of switchgrass callus and its regeneration, which also enables genetic transformation. LP9 medium is not based on Murashige and Skoog (MS) medium, the basal medium that all published switchgrass transformation has been performed. We demonstrate an efficient tissue culture system for switchgrass Alamo 2, which yields increased viability of callus and the ability to maintain callus for a duration of over 6 months. This longevity gives a greater useful callus lifetime than for published switchgrass MS-based media. This increased longevity enables greater potential efficiency and throughput for a transformation pipeline. Callus produced on LP9 is categorized as type II callus, which is more friable and easier to multiply, maintain and transfer than type I callus obtained from previously described tissue culture systems.     

Landscape heterogeneity metrics as indicators of bird diversity: Determining the optimal spatial scales in different landscapes

Species distribution models are often used to study the biodiversity of ecosystems. The modelling process uses a number of parameters to predict others, such as the occurrence of determinate species, population size, habitat suitability or biodiversity. It is well known that the heterogeneity of landscapes can lead to changes in species’ abundance and biodiversity. However, landscape metrics depend on maps and spatial scales when it comes to undertaking a GIS analysis.We explored the goodness of fit of several models using the metrics of landscape heterogeneity and altitude as predictors of bird diversity in different landscapes and spatial scales. Two variables were used to describe biodiversity: bird richness and trophic level diversity, both of which were obtained from a breeding bird survey by means of point counts. The relationships between biodiversity and landscape metrics were compared using multiple linear regressions. All of the analyses were repeated for 14 different spatial scales and for cultivated, forest and grassland environments to determine the optimal spatial scale for each landscape typology.Our results revealed that the relationships between species’ richness and landscape heterogeneity using 1:10,000 land cover maps were strongest when working on a spatial scale up to a radius of 125–250 m around the sampled point (circa 4.9–19.6 ha). Furthermore, the correlation between measures of landscape heterogeneity and bird diversity was greater in grasslands than in cultivated or forested areas. The multi-spatial scale approach is useful for (a) assessing the accuracy of surrogates of bird diversity in different landscapes and (b) optimizing spatial model procedures for biodiversity mapping, mainly over extensive areas.     

学生参与的大学校园景观设计研究—以清华大学为例

校园通过环境育人的作用潜移默化地影响着学生的成长,校园景观设计研究已成为设计类专业学生学位论文及设计课选题的主要对象之一。清华大学的教学与实践中,设计类专业学生参与校园景观营造的过程主要与其专业学习相结合,本科生与研究生各有侧重。非设计类专业学生是校园学生使用者中的多数,其参与过程以公众参与理论为指导,通过多种形式进行。合理进行资源整合与计划协调,校园景观设计研究可以成为学生价值塑造、能力培养、知识传授的理想平台。