Recruitment filtering by a moss layer disadvantages large-seeded grassland species

Calcareous grasslands are rich in biodiversity and thus receive much attention in nature conservation. In such grasslands, the formation of moss layers is perceived as a management problem. However, its impacts on the community level are complex, as not only inhibition but also facilitation of vascular plant recruitment occur. Possible filters of recruitment are shading by mosses, isolation from soil resources and the resulting desiccation. To understand how seed size and shape moderate moss effects, a combined glasshouse and field experiment was conducted in southern Germany. Seeds of 14 species from calcareous grasslands were sown either on top or underneath a moss layer, or on bare soil without moss. We determined the total number of emerged and established seedlings, i.e. the ones that survived until the end of the experiment. Both measures were reduced for most species sown on moss, while mortality was slightly enhanced by moss presence. Seed size explained a significant proportion of the moss effects on plant recruitment. Inhibitive effects on recruitment increased with seed size when seeds were placed on top of moss. When germinating underneath moss, the effect on emergence changed from negative in small-seeded plant species to positive in large-seeded species, but this effect was insignificant for establishment. The positive response in large seeds was probably due to their higher moisture requirements for imbibition, and lower dependency on light for germination. However, moss-seed-interactions were not affected by seed shape. Seedling establishment of plants with large seeds strongly depended on their initial position in moss, while small-seeded species showed no effect. Hence, moss layers constitute a selective recruitment filter by modifying seed penetration and hence germination conditions. This effect could increase beta diversity of vascular plant species in calcareous grasslands, and thus conservation should aim at intermediate and patchy moss abundance.     

The effect of flooding on the recruitment of reed marsh and tall forb plant species

Recruitment of plant species in wetlands dominated by Phragmites australis often results in a zonation of two vegetation types. A development of reed marshes takes place in the shallow flooded parts where the dominant P. australis becomes accompanied by interstitial marsh species. The vegetation on higher elevations becomes dominated by tall forbs. We investigated whether this zonation is related to the effects of flooding on the recruitment of component species of both vegetation types. All but one species had maximum germination at field capacity and germination was strongly reduced in drier soils and flooded soils. Nearly all seedlings of reed marsh species, irrespective of whether they initially supported two or six true leaves, survived eight weeks of total inundation. Survival of tall forbs was however significantly decreased by inundation. At both seedling stages a considerable number of Cirsium arvense lost their leaves when submerged, but all plants were able to recover when drained. Eupatorium cannabinum suffered extra mortality when transferred from flooded to drained conditions, whereas only young seedlings of Epilobium hirsutum died. Of all investigated species E. hirsutum was the only one with a significantly increased stem length after one week of submergence. Root porosities did not differ between reed marsh species and tall forbs but stem porosities of the reed marsh species Mentha aquatica and Lycopus europaeus were significantly higher than those of the tall forbs C. arvense and E. cannabinum. It was concluded that both reed marsh species and tall forbs require lowered water levels for germination. Flooding during the seedling stage will assign species to their position on the elevation gradient. Reed marsh species establish at lower elevations because they are best able to survive flooding and because their higher stem porosities allows them to withstand higher levels of partial submergence.     

Patch dynamics of a native grass in relation to the spread of invasive smooth brome (Bromus inermis)

The effects of invasive species on the patch dynamics (establishment, growth, and local extinction) of native species are not well studied, owing to the need for relatively fine-scale data on the distribution of species. Within the prairie pothole region of the United States and Canada, the grass, Bromus inermis (smooth brome) has become established by invading disturbed prairies, and through repeated introductions for soil retention and animal graze. In this study, the impact of smooth brome on the patch dynamics of a dominant native grass species, Spartina pectinata (prairie cordgrass), was assessed using fine-scale (sub-meter) mapping of the distribution of cordgrass and brome in three prairie fragments from 2000 to 2006. Using GIS spatial analyses, we determined that cordgrass patch growth was two times greater in areas not invaded by smooth brome versus areas that were heavily infested with smooth brome. Among sites and time periods, there was a consistent significant negative relationship between the amount of smooth brome surrounding a patch of cordgrass and the growth of that cordgrass patch. The probability of establishment of a new patch of cordgrass averaged 1.3 times higher in areas of low brome coverage (<25%) than areas of high brome coverage (>75%). Conversely, existing cordgrass patches were 7.8 times more likely to go extinct in areas of high than low brome coverage. This is one of only a few field studies to provide evidence of the negative impact of smooth brome on native flora and hopefully will serve as justification for the development of a formal management plan to limit the distribution of this species in tallgrass prairie ecosystems.     

Cohesin Acetylation Promotes Sister Chromatid Cohesion Only in Association with the Replication Machinery

Acetylation of the Smc3 subunit of cohesin is essential to establish functional cohesion between sister chromatids. Smc3 acetylation is catalyzed by members of the Eco family of acetyltransferases, although the mechanism by which acetylation is regulated and how it promotes cohesion are largely unknown. In vertebrates, the cohesin complex binds to chromatin during mitotic exit and is converted to a functional form during or shortly after DNA replication. The conserved proliferating cell nuclear antigen-interacting protein box motif in yeast Eco1 is required for function, and cohesin is acetylated during the S phase. This has led to the notion that acetylation of cohesin is stimulated by interaction of Eco1 with the replication machinery. Here we show that in vertebrates Smc3 acetylation occurs independently of DNA replication. Smc3 is readily acetylated before replication is initiated and after DNA replication is complete. However, we also show that functional acetylation occurs only in association with the replication machinery: disruption of the interaction between XEco2 and proliferating cell nuclear antigen prevents cohesion establishment while having little impact on the overall levels of Smc3 acetylation. These results demonstrate that Smc3 acetylation can occur throughout interphase but that only acetylation in association with the replication fork promotes sister chromatid cohesion. These data reveal how the generation of cohesion is limited to the appropriate time and place during the cell cycle and provide insight into the mechanism by which acetylation ensures cohesion.     

Construction of bacteria–eukaryote synthetic mutualism

Mutualism is ubiquitous in nature but is known to be intrinsically vulnerable with regard to both population dynamics and evolution. Synthetic ecology has indicated that it is feasible for organisms to establish novel mutualism merely through encountering each other by showing that it is feasible to construct synthetic mutualism between organisms. However, bacteria–eukaryote mutualism, which is ecologically important, has not yet been constructed. In this study, we synthetically constructed mutualism between a bacterium and a eukaryote by using two model organisms. We mixed a bacterium, Escherichia coli (a genetically engineered glutamine auxotroph), and an amoeba, Dictyostelium discoideum, in 14 sets of conditions in which each species could not grow in monoculture but potentially could grow in coculture. Under a single condition in which the bacterium and amoeba mutually compensated for the lack of required nutrients (lipoic acid and glutamine, respectively), both species grew continuously through several subcultures, essentially establishing mutualism. Our results shed light on the establishment of bacteria–eukaryote mutualism and indicate that a bacterium and eukaryote pair in nature also has a non-negligible possibility of establishing novel mutualism if the organisms are potentially mutualistic.     

Neopolyploidy and diversification in Heuchera grossulariifolia

Newly formed polyploid lineages must contend with several obstacles to avoid extinction, including minority cytotype exclusion, competition, and inbreeding depression. If polyploidization results in immediate divergence of phenotypic characters these hurdles may be reduced and establishment made more likely. In addition, if polyploidization alters the phenotypic and genotypic associations between traits, that is, the P and G matrices, polyploids may be able to explore novel evolutionary paths, facilitating their divergence and successful establishment. Here, we report results from a study of the perennial plant Heuchera grossulariifolia in which the phenotypic divergence and changes in phenotypic and genotypic covariance matrices caused by neopolyploidization have been estimated. Our results reveal that polyploidization causes immediate divergence for traits relevant to establishment and results in significant changes in the structure of the phenotypic covariance matrix. In contrast, our results do not provide evidence that polyploidization results in immediate and substantial shifts in the genetic covariance matrix.     

重组酶聚合酶等温扩增快速检测肺炎支原体方法的建立和初步应用

摘要 目的：建立基于重组酶聚合酶扩增技术（RPA）技术快速检测肺炎支原体的方法。方法：本研究以肺炎支原体编码P1黏附蛋白为靶基因,利用Primer Premier 5软件进行引物、探针的设计,最终筛选出最佳引物。同时设计相应的实时荧光定量PCR（RT-PCR）引物用于后续的验证试验。对反应体系试剂比例、反应时间、反应温度、引物探针浓度进行确定。肺炎支原体、解脲支原体、人型支原体、肺炎克雷伯菌、肺炎双球菌、大肠杆菌和链球菌作为对照评估RPA检测肺炎支原体的特异性及敏感度。结果：RPA快速检测肺炎支原体方法仅需14 min,检测灵敏度达200 copies/mL;6种非肺炎支原体均不能扩增,特异性较高。结论：本研究建立了肺炎支原体的RPA快速检测方法,具有迅速、简便、经济等优势,为肺炎支原体的快速检测提供一个新的有利工具。     

Isolation affects tree‐scale epiphytic lichen community structure on New Zealand mountain beech trees

Question: Is epiphytic lichen community structure significantly affected by isolation from source community? Location: Foothills of the Southern Alps, South Island, New Zealand. Methods: Epiphytic lichen richness and environmental variables were measured on 382, young Nothofagus solandri var. cliffortioides (Hook. f.) Poole (mountain beech) trees that had recently colonized grassland adjacent to a forest remnant. Richness and the presence of individual lichen taxa were modelled as a function of isolation from the forest fragment, tree size and other habitat conditions. Results: Richness of epiphytic lichen communities was negatively related to tree isolation, although this effect was much smaller than the effects of tree size and other local (tree‐scale) habitat conditions. Different lichen taxa responded in different ways to isolation, area effects and local habitat conditions. Conclusions: This study shows that many epiphytic lichens on mountain beech are limited in their ability to colonize new substrate, even over distances of less than 1 km, which may be due to limitation in dispersal and/or establishment. Lichens are greatly influenced by local habitat conditions, such as tree size, and in this particular environment their negative interaction with sooty moulds is an important driver of community structure.     

Pine weevil damage to Norway spruce seedlings: effects of nutrient‐loading,soil inversion and physical protection during seedling establishment

• 1 The pine weevil Hylobius abietis (L.) feeds on the bark of young conifer seedlings and is one of the most economically important forest pests in Europe.
• 2 In a field experiment, we examined the combined effects of the treatments: nutrient‐loading of seedlings, planting in scarified plots and protection of seedlings against pine weevil damage for either half a season or a full season.
• 3 Nutrient loading had no significant effect on the amount of pine weevil feeding.
• 4 Seedling mortality was significantly reduced when seedlings were protected from pine weevil feeding during establishment. This occurred even though the debarked area of protected seedlings 5 weeks after the shields had been removed was similar to that of the unprotected seedlings. This indicates that initial protection rendered the seedlings more tolerant to later wounding by pine weevil.
• 5 Planting in soil inversion significantly reduced feeding compared with planting in humus.
• 6 We conclude that nutrient‐loading of seedlings in the autumn before planting would not increase pine weevil feeding after planting. Mortality could be reduced by treatments that postpone the start of pine weevil feeding on seedlings. Such treatments, combined with planting in soil inversion, would result in increased seedling growth, vitality and tolerance to pine weevil attack.

     

山羊传染性胸膜肺炎病原快速诊断方法的建立

为准确快速鉴定临床疑似山羊传染性胸膜肺炎(CCPP)病原,针对丝状支原体山羊亚种(Mmc)与绵羊肺炎支原体(Mo)16S rRNA基因设计两对特异性引物Ps/Pa、Ms/Ma,通过优化反应条件及体系,建立检测CCPP两种主要致病支原体的双重PCR方法,并检测了所建方法特异性、敏感性及临床应用。当引物、Mg2+及dNTP浓度分别为0.8 pmol/μL、1.5 nmol/μL、0.2 nmol/μL,Ps/Pa与Ms/Mo比例为1 1时,于54℃退火40 s,可最小检出Mmc与Mo核酸量分别为0.1 ng、0.01 ng,敏感性良好。通过特异性与临床疑似病例检测,证明所建方法具较好特异性,可初步应用于临床诊断。