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

C₄ 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.     

Tolerance of switchgrass to extreme soil moisture stress: Ecological implications

Switchgrass (Panicum virgatum L.), a native of eastern and central North America, is a leading candidate as a dedicated biofuel feedstock in the US due to its broad adaptability, rapid growth rate, and ability to grow in low production soils. To begin to characterize the important agronomic and ecological traits related to environmental tolerance of switchgrass, we evaluated fitness under stressful growing conditions. We assessed the germination, establishment, performance, and reproductive potential of four common accessions, both upland and lowland ecotypes, at various levels of soil moisture availability (moisture deficit to flooded) in the greenhouse. Seeds emerged and established (55–90% survival) under all soil moisture conditions (−0.3 MPa to flooded). Transplants of lowland ecotypes performed as well in flooded conditions as in field capacity controls, though flooding reduced performance of upland ecotypes. Drought treatments (−4.0 and −11.0 MPa) reduced tiller length and number, leaf area, and biomass production by up to 80%. However, once established, all plants survived at −4.0 MPa and had the same proportion of tillers in flower as at field capacity. The ability of switchgrass to germinate, establish, and flower in low moisture and flooded conditions, particularly lowland ecotypes, may increase the range of environments suitable for biofuel cultivation, and can serve as a baseline for further ecological studies and genetic improvement.     

Characterization of culturable bacterial endophytes of switchgrass (Panicum virgatum L.) and their capacity to influence plant growth

Switchgrass (Panicum virgatum L.) is a perennial warm season grass that is native to the plains of North America and is widely grown as a forage, bioenergy or groundcover crop. Despite its importance, a bottleneck in switchgrass production is poor seedling vigor, which as a perennial crop represents an important time for management. Herein, data identify a suite of culturable bacterial microflora extracted from switchgrass, and show their capability to influence host plant growth and development. A total of 307 bacterial isolates were cultured and isolated from surface sterilized switchgrass biomass and sequence identified into 76 strains (subspecies classification), 36 species and 5 phyla. Approximately 58% of bacterial strains, when reintroduced into surface‐sterilized switchgrass seeds, were documented to increase lamina length (cm from base to tip after 60 days growth) relative to uninoculated controls. Ecologically, Phylum Firmicutes was the most abundant bacterial classification and encompassed 75% of all isolates. Although the culturable bacterial community studies herein represent an unknown and assumedly minor proportion of the total microbiome, by focusing on culturable bacteria, we delineate functional feedback between the presence of isolated bacteria and switchgrass seedling growth.     

Population Dynamics of Plant Nematodes in Cultivated Soil: Effect of Summer Cover Crops in Old Agricultural Land

In a 6-year cover crop sequence study, nematode population densities varied with different cover crops. Millet favored rapid increase of Belonolaimus longicaudatus and supported relatively large numbers of Pratylenchus brachyurus. Beggarweed and ''Coastal'' bermudagrass favored rapid increase of B. Iongicaudatus and to a lesser extent P. brachyurus and Trichodorus christiei. Hairy indigo and Crotalaria supported relatively large numbers of P. brachyurus but suppressed B. longicaudatus. Hairy indigo also supported increases of T. christiei and Xiphinema americanum. Marigold did not favor development of any parasitic nematode species present. Tomato transplant yield was inversely related to nematode population, particularly to B. Iongicaudatus. Largest yields were obtained from plots with smallest numbers of B. longicaudatus and smallest yields were from plots with largest numbers of B. longicaudatus.     

Genetic Structure of Remnant Populations and Cultivars of Switchgrass (Panicum virgatum) in the Context of Prairie Conservation and Restoration

Switchgrass (Panicum virgatum L.) is a dominant, perennial C₄ grass of North American tallgrass prairies with cultivars that are widely used in grassland restoration, pastures, and landscaping. However, these cultivars may be genetically dissimilar to small, remnant populations, raising concerns about altered genetic composition of native populations through gene flow. To address this issue on a local scale in Ohio and Illinois, we used microsatellite markers to characterize genetic diversity and differentiation of 10 remnant prairie populations (5 in each state) and 8 common cultivars. The bulk of genetic variation was found to reside within rather than among wild populations, consistent with the outcrossing breeding system of switchgrass. Genetic diversity was similar among the remnant populations despite large differences in area (approximately 2–2,590 ha), highlighting the importance of small native populations as reservoirs of variation and potential seed sources for prairie restoration. Cultivars generally had similar levels of variation to the wild populations, but we found clear genetic dissimilarity between wild and cultivated gene pools (especially for Kanlow, but also Trailblazer, Blackwell, Dacotah, Summer, and Sunburst cultivars). This suggests that using cultivars in local prairie restoration efforts may alter the genetic composition of wild populations. Whether such changes are deemed as negative depends on the cultivar under consideration and specific conservation goals for preserving native switchgrass populations. Patterns of genetic variation in remnant prairie populations and potential cultivar sources can be used to develop guidelines for restoration as well as future planting of cultivars for biofuels.     

Functional Genomics of Drought Tolerance in Bioenergy Crops

With predicted global changes in temperature and precipitation, drought will increasingly impose a challenge to biomass production. Most of the bioenergy crops have some degree of drought susceptibility as revealed for example through measures of low water-use efficiency (WUE). It is imperative to improve drought tolerance and WUE in bioenergy crops for sustainable biomass production in arid and semi-arid regions. Genetics and functional genomics can play critical roles in generating knowledge to inform and aid genetic improvement for drought tolerance in bioenergy crops. The molecular aspects of drought response have been extensively investigated in model plants like Arabidopsis, yet our understanding of the molecular mechanisms underlying drought tolerance in bioenergy crops is limited. Plants in general exhibit various responses to drought stress depending on species and genotype. A rational strategy for studying drought tolerance in bioenergy crops is to translate the knowledge from model plants relative to the unique features associated with individual bioenergy species and genotypes. In this review, we summarize the general knowledge concerning drought responsive pathways, with a focus on the identification of commonality and specialty in drought responsive mechanisms among alternate species and genotypes. We describe the genomic resources developed for bioenergy crops and discuss genetic and epigenetic regulation of drought responses. We also examine comparative and evolutionary genomics as a means to leverage the ever-increasing genomics resources and provide new insights beyond what is known from studies on individual species. Finally, we outline future opportunities for studying drought tolerance using the emerging technologies.     

利用SCoT分析柳枝稷遗传资源的多样性

本研究利用SCoT标记对96份柳枝稷种质的亲缘关系和遗传变异进行了研究。筛选出20条引物对96份供试材料进行PCR扩增,共获得445条带,其中多态性条带402条,平均多态性条带比率(PPB)达90.31%,多态性信息含量(PIC)为0.166~0.410,平均值为0.332,标记指数(MI)为10.20。遗传相似系数(GS)为0.498~0.912,平均值为0.688。表明SCoT标记能够揭示柳枝稷种质间的遗传变异。通过UPGMA分析表明,96份种质资源聚为高地型和低地型两大类。经POPGENE1.32软件分析结果显示:96份柳枝稷基因多样性指数(H)为0.285,Shannon指数(I)为0.431,表明供试的种质间遗传多样性丰富,遗传多样性水平高。经AMOVA 1.55方差分析揭示:96份柳枝稷生态型内的遗传变异占总变异的72.85%,生态型间遗传变异占总变异的27.15%,结果表明ScoT可用于柳枝稷遗传多样性研究,该研究结果可为柳枝稷种质资源的进一步开发利用提供重要信息。     

Construction of a GFP-BAR plasmid and its use for switchgrass transformation

 A dual marker plasmid comprising the reporter gene sgfp (green fluorescent protein) and the selectable bar gene (Basta tolerance) was constructed by replacing the uidA (β-glucuronidase, GUS) gene in a uidA-bar construct with sgfp. A particle inflow gun was used to propel tungsten particles coated with this plasmid into immature inflorescence-derived embryogenic callus of switchgrass (Panicum virgatum L.). GFP was observed in leaf tissue and pollen of transgenic plants. Nearly 100 plants tolerant to Basta were obtained from the experiments, and Southern blot hybridization confirmed the presence of both the bar and sgfp genes. Plants regenerated from in vitro cultures of transgenic plants grew on medium with 10 mg l^–1 bialaphos. When the pH indicator chlorophenol red was in the medium, the transgenic plantlets changed the medium from red to yellow. Basta tolerance was observed in T₁ plants resulting from crosses between transgenic and nontransgenic control plants, indicating inheritance of the bar transgene. Received: 11 May 2000 / Revision received: 21 August 2000 / Accepted: 22 August 2000     

异质养分环境中一年生分蘖草本黍根系的生长特征

为揭示黍（Panicum miliaceum L.)根系对异质养分环境的生长反应,作研究了黍根系从起始斑块向目标斑块水平生长时,时始斑块和目标斑块养分水平根生长的影响,就低养分起始珏块而言,粗根生物量,粗根长度,粗根表面积和细极长度在高养分目标斑块中的分配比例均小于其在低养分目标斑块中的分配比例,而细根长度及其密度,细根表面积指及其密度的变化恰好相反,就高养分起始斑块而言,高养分目标斑块的细根长度,细根长度密度,细根表面积指数和细根表面积密均不于低养分目标斑块,而粗根对目标斑块中养分状的反应不明显。当黍根系从桢的起始斑块进入不同的目标斑块后,目标斑块的养分状况对细根生物量及其分配无影响,而显影响细根长度和表现积,这指示细根是通过长度和表面积可塑性而不是生物量变化响应目标斑块中的养分差异。     

An integrative insight on dormancy alleviation in diaspores of Urochloa humidicola (Rendle) Morrone & Zuloaga,a tropical grass with great economic and ecological impact

• Even though exhaustively studied, dormancy alleviation in diaspores of Urochloa humidicola (Rendle) Morrone & Zuloaga remains a mystery. To clarify this, we asked the following question: could dormancy alleviation in diaspores of this species be associated with ageing, GA/ABA balance and remaining structures of the panicoid spikelet?
• We answer this question using diaspores of U. humidicola cv. BRS Tupi as a biological model, a cultivar with a wide edaphoclimatic range in Neotropical areas and whose diaspores possess ‘deep dormancy’ when dispersed. We analysed both germination and early plant development using a split‐plot model.
• Our findings demonstrate that dormancy alleviation in diaspores of U. humidicola is a synergic phenomenon driven by crosstalk between age, GA/ABA balance and remaining structures of the panicoid spikelet covering caryopses, since this interaction acts on the dynamics of germination and early plant development.
• We demonstrate that: (i) spreading germination time is a maternal survival mechanism of this species, which has repercussions for occupational aggressiveness of the species; (ii) remaining structures of the panicoid spikelet covering caryopses are the main modulator of embryo development. These structures control the after‐ripening process, which is modulated by some molecular factor. We also highlight that it is necessary to review concepts about dormancy of dispersal units in this grass species.