Endo-allopolyploidy of autopolyploids and recurrent hybridization—A possible mechanism to explain the unresolved Y-genome donor in polyploid Elymus species (Triticeae: Poaceae)

The genus Elymus L. in the tribe Triticeae (Poaceae) includes economically and ecologically important forage grasses. The genus contains the pivotal St genome from Pseudoroegneria in combination with other genomes in the tribe. Many Elymus species are tetraploids containing the StY genomes. It is thought that polyploidization characterizes the speciation of the genus in which the Y is considered as another key genome. Based on data from cytological, genome in situ hybridization, and molecular studies, we hypothesized an endo-allopolyploidy origin of the StY-genome species from the autotetraploid Pseudoroegneria species. To test this hypothesis, we amplified, cloned, and sequenced five single-copy nuclear genes (i.e., alcohol dehydrogenase 1–3, Adh1–Adh3, RNA polymerase II, Rpb2; and Waxy) from Elymus, Pseudoroegneria, and Hordeum species. The phylogenetic trees constructed based on the sequencing analyses of all genes indicated that diploid and autotetraploid Pseudoroegneria species were closely related, although with considerable genetic variation in tetraploids. In addition, the StY-genome Elymus species tended to have a close relationship with the diploid and autotetraploid Pseudoroegneria species, although different phylogenetic relationships among the gene trees were detected. These results indicated that the StY-genome species may have an autotetraploid origin and experienced recurrent hybridization. The complex St genomes in Pseudoroegneria in the polyploid state may gain more opportunities for within-species differentiation and recurrent hybridization. As a result, series modified versions of St genomes evolved into the StY genomes in some Elymus species.     

Experimental and Modelling Studies of Competition for Light in Roadside Grasses

Equiproportional mixtures and monocultures of two roadside grass species (Elymus repens (L.) Gould and Puccinellia distans (L.) Pari.) were grown in experimental field plots under non-limiting water and nutrient conditions. During the course of the season, E. repens increasingly overgrew and shaded plants of P. distans which eventually died. A multispecies canopy photosynthesis model was parameterized using measurements of structural and physiological characteristics from three different stages of canopy development. Results of simulations clearly revealed that canopy photosynthesis of P. distans was highly dependent on the degree of light competition caused by E. repens. Since P. distans has recently invaded stands of roadside vegetation throughout Central Europe where it has replaced the native and highly competitive E. repens, it is hypothesized that this success is due to disturbance factors that keep E. repens from growing tall and shading P. distans.     

Elymus与普通小麦属间杂种的细胞遗传学研究

本研究以Elymus pendulinus(Nevski)Tzvelev(2n=4x=28,SSYY)、E.shandongenisis B.Salomon(2n=4x=28,SSYY)与普通小麦(Triticum aestivum L.:2n=6x=42,AABBDD)进行了属间远缘杂交。通过对杂种胚的离体培养,两个组合均产生了杂种F_1植株。杂种F_1为多年生,植株生长旺盛;形态上介于亲本种之间而兼具双亲的某些特征;穗状花序发育正常,但均完全不育。两个组合的根尖和花粉母细胞染色体数目为2n-5x=35。通过对杂种减数分裂染色体配对行为的分析,发现其MI染色体的配对水平很低,二价体均为棒状,每细胞的平均染色体交叉数在0.25-0.31之间。这表明E.pendulinus t E.shandongensis 所含的SY染色体组与普通小麦的ABD染色体之间的同源程度很低。由于在E.shandongeasis 及其它具有SY染色体组的Elymus 单倍体中,SY染色体组之间的部份同源染色体配对数均明显高于该杂种中的配对数,这表明存在于普通小麦中的ph基因及其它具类似作用的基因系统能抑制SY染色体组之间的部份同源染色体配对。     

披碱草属3个种的核型研究

首次报道了我国青藏高原３种披碱草属植物的核型,即短荒披碱草核型为２ｎ＝６ｘ＝４２＝３２ｍ＋１０ｓｍ（４ＳＡＴ）,属２Ａ类型无芳芒披碱草,核型为２ｎ＝６ｘ＝４２＝３０ｍ＋１２ｍ（２ＳＡＴ）,属２Ａ类型;硕穗披碱草,核型为２ｎ＝６ｘ＝４２＝３２ｍ＋１０ｓｍ（４ＳＡＴ）,属２Ｂ类型。     

Effects of UV-B radiation on terrestrial plants and ecosystems: interaction with CO2 enrichment

UV-B radiation is just one of the environmental factors, that affect plant growth. It is now widely accepted that realistic assessment of plant responses to enhanced UV-B should be performed at sufficiently high Photosynthetically Active Radiation (PAR), preferably under field conditions. This will often imply, that responses of plants to enhanced UV-B in the field will be assessed under simultaneous water shortage, nutrient deficiency and variation of temperature. Since atmospheric CO₂ enrichment, global warming and increasing UV-B radiation represent components of global climatic change, interactions of UV-B with CO₂ enrichment and temperature are particularly relevant. Only few relevant UV-B× CO₂ interaction studies have been published. Most of these studies refer to greenhouse experiments. We report a significant CO₂ × UV-B interaction for the total plant dry weight and root dry weight of the C₃-grass Elymus athericus. At elevated CO₂ (720 mol mol^-1, plant growth was much less reduced by enhanced UV-B than at ambient atmospheric CO₂ although there were significant (positive) CO₂ effects and (negative) UV-B effects on plant growth. Most other CO₂ × UV-B studies do not report significant interactions on total plant biomass. This lack of CO₂ × UV-B interactions may result from the fact that primary metabolic targets for CO₂ and UVB are different. UV-B and CO₂ may differentially affect plant morphogenetic parameters: biomass allocation, branching, flowering, leaf thickness, emergence and senescence. Such more subtle interactions between CO₂ and UV-B need careful and long term experimentation to be detected. In the case of no significant CO₂× UV-B interactions, combined CO₂ and UV-B effects will be additive. Plants differ in their response to CO₂ and UV-B, they respond in general positively to elevated CO₂ and negatively to enhanced UV-B. Moreover, plant species differ in their responsiveness to CO₂ and UV-B. Therefore, even in case of additive CO₂ and UV-B effects, plant competitive relationships may change markedly under current climatic change with simultaneous enhanced atmospheric CO₂ and solar UV-B radiation.     

Growth, gas exchange, leaf nitrogen and carbohydrate concentrations in NAD‐ME and NADP‐ME C4 grasses grown in elevated CO2

Plants with the C₄ photosynthetic pathway have predominantly one of three decarboxylation enzymes in their bundle sheath cells. Within the grass family (Poaceae) bundle sheath leakiness to CO₂ is purported to be lowest in the nicotinamide adenine dinucleotide phosphate-malic enzyme (NADP-ME, EC 1.1.1.40) group, highest in the NAD-ME (EC 1.1.1.39) group and intermediate in the phosphoenolpyruvate carboxykinase (PCK, EC 4.1.1.32) group. We investigated the hypothesis that growth and photosynthesis of NAD-ME C₄ grasses would respond more to elevated CO₂ treatment than NADP-ME grasses. Plants were grown in 8-1 pots in growth chambers with ample water and fertilizer for 39 days at a continuous CO₂ concentration of either 350 or 700 µl l^?1. NAD-ME species included Bouteloua gracilis Lag. ex Steud (Blue grama), Buchloe dactyloides (Nutt.) Engelm. (Buffalo grass) and Panicum virgatum L. (Switchgrass) and the NADP-ME species were Andropogon gerardii Vittman (Big bluestem), Schizachyrium scoparium (Michx.) Nash (Little bluestem), and Sorghastrum nutans (L.) Nash (Indian grass). Contrary to our hypothesis, growth of the NADP-ME grasses was generally greater under elevated CO₂ (significant for A. gerardii and S. nutans), while none of the NAD-ME grasses had a significant growth response. Increased leaf total non-structural carbohydrate (TNC) was associated with greater growth responses of NADP-ME grasses. Decreased leaf nitrogen in NADP-ME species grown at elevated CO₂ was found to be an artifact of TNC dilution. Assimilation (A) vs intercellular CO₂ (C_i) curves revealed that leaf photosynthesis was not saturated at 350 µl l^?1 CO₂ in any of these C₄ grasses. Assimilation of elevated CO₂-grown A. gerardii was higher than in plants grown in ambient CO₂. In contrast, B. gracilis grown in elevated CO₂ displayed lower A, a trait more commonly reported in C₃ plants. Photosynthetic acclimation in B. gracilis was not related to leaf TNC or nitrogen concentrations, but A:C_i curves suggest a reduction in activity of both phosphoenolpyruvate (PEP) carboxylase (EC 4.1.1.31) and ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco, EC 4.1.1.39). Some adaptation of stomatal functioning was also seen in B. gracilis and A. gerardii leaves grown in elevated CO₂. Our study shows that C₄ grasses have the capacity for increased growth and photosynthesis under elevated CO₂ even when water and nutrients are non-limiting. While it was the NADP-ME species which had significant responses in the present study, we have previously reported significant growth increases in elevated CO₂ for B. gracilis.     

垂穗披硷草个体大小与种群密度的关系

本文以垂穗披硷草为材料研究了多年生植物群个体大小与密度的关系。研究结果表明,垂穗披硷草个体生物量与密度间的直线回归斜率β的绝对值于生长初期较小,随着生长时间的延长有所增加,但最大的β绝对值仅为１．０２从未达到－３／２。单株分孽数与密度间的回归斜率始终保持在较小的绝对值上。生活第三年种群密度对自生幼苗具有一定的影响。     

An ecosystem-level perspective of allelopathy

Allelopathy is an interference mechanism by which plants release chemicals which affect other plants; while it has often been proposed as a mechanism for influencing plant populations and communities, its acceptance by plant ecologists has been limited because of methodological problems as well as difficulties of relating the results of bioassays used for testing allelopathy to vegetation patterns in the field. Here we argue that the concept of allelopathy is more appropriately applied at the ecosystem-level, rather than the traditional population/community level of resolution. Firstly, we consider the wide ranging effects of secondary metabolites (widely regarded as allelochemicals) on organisms and processes which regulate ecosystem function, including herbivory, decomposition and nutrient mineralization. It is apparent that plants with allelopathic potential against other organisms induce net changes in ecosystem properties, which may in turn impact upon the plant community in the longer term. We then illustrate these concepts using two contrasting examples of how invasive plant species with allelopathic potential may alter ecosystem properties through the production of secondary metabolites, i.e. Carduus nutans (nodding thistle) in New Zealand pastures and Empetrum hermaphroditum (crowberry) in Swedish boreal forests. In both cases the production of secondary metabolites by the invasive species induces important effects on other organisms and key processes, which help determine how the ecosystem functions and ultimately the structure of the plant community. These examples help demonstrate that the concept of allelopathy is most effectively applied at the ecosystem-level of resolution, rather than at the population-level (i.e. plant-plant interference).     

Comparison of the Giemsa C-banded and N-banded karyotypes of twoElymus species,E. dentatus andE. glaucescens (Poaceae: Triticeae)

The karyotypes ofElymus dentatus from Kashmir andE. glaucescens from Tierra del Fuego, both carrying genomesS andH, were investigated by C- and N-banding. Both taxa had 2n = 4x = 28. The karyotype ofE. dentatus was symmetrical with large chromosomes. It had 18 metacentric, four submetacentric and six satellited chromosomes. The karyotype ofE. glaucescens resembled that ofE. dentatus, but a satellited chromosome pair was replaced by a morphologically similar, non-satellited pair. The C-banding patterns of both species had from one to five conspicuous and a few inconspicuous bands per chromosome. N-banding differentiated the chromosomes of the constituent genomes by producing bands in theH genome only. TheS genomes of both species were similar with five metacentric and two satellited chromosomes having most conspicuous C-bands at telomeric and distal positions. They resembled theS genome of the genusPseudoroegneria. TheH genomes had four similar metacentric and two submetacentric chromosomes. The seventhH genome chromosome ofE. dentatus was satellited, that ofE. glaucescens nonsatellited, but otherwise morphologically similar. The C-bands were distributed at no preferential positions. TheH genome ofE. dentatus resembles theH genomes of some diploidHordeum taxa.     

生化他感作用与高寒草甸上人工草场自然退化现象的研究

细叶亚菊是海北地区垂穗披碱草人工草场上主要入侵杂草之一。本文探讨了垂穗披碱草和细叶亚菊草种间抑制与促进作用以及细叶亚菊各种代谢产物对垂穗披碱草种子萌发与幼苗生长的抑制作用。实验表明:在垂穗披碱草人工草场自然退化过程中存在着生化他感作用。牧草的自然退化速度与主要杂草入侵程度呈明显的相关性。