A physiological analogy of the niche for projecting the potential distribution of plants

Aim  To develop a physiologically based model of the plant niche for use in species distribution modelling. Location  Europe. Methods  We link the Thornley transport resistance (TTR) model with functions which describe how the TTR’s model parameters are influenced by abiotic environmental factors. The TTR model considers how carbon and nutrient uptake, and the allocation of these assimilates, influence growth. We use indirect statistical methods to estimate the model parameters from a high resolution data set on tree distribution for 22 European tree species. Results  We infer, from distribution data and abiotic forcing data, the physiological niche dimensions of 22 European tree species. We found that the model fits were reasonable (AUC: 0.79–0.964). The projected distributions were characterized by a false positive rate of 0.19 and a false negative rate 0.12. The fitted models are used to generate projections of the environmental factors that limit the range boundaries of the study species. Main conclusions  We show that physiological models can be used to derive physiological niche dimensions from species distribution data. Future work should focus on including prior information on physiological rates into the parameter estimation process. Application of the TTR model to species distribution modelling suggests new avenues for establishing explicit links between distribution and physiology, and for generating hypotheses about how ecophysiological processes influence the distribution of plants.     

The effects of xylanase type enzymes on the different layers of birch wood ORGANOSOLV pulp fibre walls

Some effects of the xylanase treatment on the separate birch ORGANOSOLV pulp fibre wall morphological layers were examined. These investigations were focused on the outer layers, i.e. the primary wall (P) and the outer layer of the secondary wall (S₁), as well as the central layers, i.e. the central layer of the secondary wall (S₂) and the tertiary wall (T). Step by step, the fractionation of the pulp components in the polar solvents N,N-dimethylformamide (DMFA), dimethylsulphoxide (DMSO) and DMSO/H₃PO₄ was used as a mild technique for the isolation of the lignin-carbohydrate complexes. The different residual amounts of lignin and hemicelluloses in the outer and central pulp fibre wall layers as well as the different lignin-hemicellulose ratios were determined. The size-exclusion chromatographical (SEC) analysis showed a higher initial lignin content in the region of the high molecular mass (MM) fibre wall fraction extracted with “DMSO/H₃PO₄” than the outer cell wall layers. In the central layers, the amounts of soluble lignin (calculated on the mass of total dissolved substance) were approximately the same for all the three solvents. The xylanase treatment brought the most considerable changes in the high MM part of the residual lignin (the lignin carbohydrate complex). This was true for both the P-S₁ and S₂-T layers. The careful brightness comparison of the outer and central fractions after the X-E-P-P bleaching sequence showed a surprisingly low bleachability of the outer layer fraction. The xylanase action depended on the composition of the lignin-carbohydrate complex (LCC) and the extent of the maintenance of the outer layers during the pulping process.     

Big flies, small repeats: the "Thr-Gly" region of the period gene in Diptera

The region of the clock gene period (per) that encodes a repetitive tract of threonine-glycine (Thr-Gly) pairs has been compared between Dipteran species both within and outside the Drosophilidae. All the non- Drosophilidae sequences in this region are short and present a remarkably stable picture compared to the Drosophilidae, in which the region is much larger and extremely variable, both in size and composition. The accelerated evolution in the repetitive region of the Drosophilidae appears to be mainly due to an expansion of two ancestral repeats, one encoding a Thr-Gly dipeptide and the other a pentapeptide rich in serine, glycine, and asparagine or threonine. In some drosophilids the expansion involves a duplication of the pentapeptide sequence, but in Drosophila pseudoobscura both the dipeptide and the pentapeptide repeats are present in larger numbers. In the nondrosophilids, however, the pentapeptide sequence is represented by one copy and the dipeptide by two copies. These observations fulfill some of the predictions of recent theoretical models that have simulated the evolution of repetitive sequences.      

Excitation of System I and System II in Photosynthesis as a Possible Control Mechanism of Glycolate Metabolism in the Blue-Green Alga Anacystis nidulans

Photosynthetic enhancement studies performed at 619 nm (excitation of Systems I and II) and at 446 nm (mainly excitation of System I) revealed an 18% photosynthetic enhancement simultaneously with a 31% reduction in glycolate excretion. This observation supports the hypothesis that some glycolate may be consumed in an oxidation process associated with System I when System II is poorly excited and the supply of electrons from the water splitting process of photosynthesis is low.     

土壤中棉花黄萎病菌SYBR Green Ⅰ荧光RT-PCR定量检测技术研究

为实现田间土壤棉花黄萎病菌的早期检测,建立了土壤中棉花黄萎病菌的SYBR Green I荧光定量PCR检测方法。以含342bp PCR扩增产物的阳性质粒为参考,构建了标准曲线,并对该曲线的特异性、敏感性、可重复性进行了评价。结果表明,该方法具有快速、特异性强、敏感度高等特点。检测范围在3.8×103-3.8×108copies/μL之间有良好的线性关系,相关系数R2为0.996,扩增效率为101.5%,灵敏度比常规PCR方法高102倍。     

Last glacial maximum biomes reconstructed from pollen and plant macrofossil data from northern Eurasia

Pollen and plant macrofossil data from northern Eurasia were used to reconstruct the vegetation of the last glacial maximum (LGM: 18,000 ± 2000 ¹⁴C yr bp ) using an objective quantitative method for interpreting pollen data in terms of the biomes they represent ( Prentice et al., 1996 ). The results confirm previous qualitative vegetation reconstructions at the LGM but provide a more comprehensive analysis of the data. Tundra dominated a large area of northern Eurasia (north of 57°N) to the west, south and east of the Scandinavian ice sheet at the LGM. Steppe‐like vegetation was reconstructed in the latitudinal band from western Ukraine, where temperate deciduous forests grow today, to western Siberia, where taiga and cold deciduous forests grow today. The reconstruction shows that steppe graded into tundra in Siberia, which is not the case today. Taiga grew on the northern coast of the Sea of Azov, about 1500 km south of its present limit in European Russia. In contrast, taiga was reconstructed only slightly south of its southern limit today in south‐western Siberia. Broadleaved trees were confined to small refuges, e.g. on the eastern coast of the Black Sea, where cool mixed forest was reconstructed from the LGM data. Cool conifer forests in western Georgia were reconstructed as growing more than 1000 m lower than they grow today. The few scattered sites with LGM data from the Tien‐Shan Mountains and from northern Mongolia yielded biome reconstructions of steppe and taiga, which are the biomes growing there today.     

Heliobacterium sulfidophilum sp. nov. andHeliobacterium undosum sp. nov.: Sulfideoxidizing heliobacteria from thermal sulfidic springs

Two new species of heliobacteria isolated from cyanobacterial mats of two alkaline sulfidic hot springs are formally described. Strains BR4 and BG29 are assigned to anoxygenic phototrophic bacteria of the familyHeliobacteriaceae, since they possess the unique properties of this taxon: strict anaerobiosis, formation of bacteriochlorophyllg, the lack of extensive intracytoplasmic membranes and chlorosomes, an unusual cell wall structure, and phylogenetic relatedness to the low G+C gram-positive eubacteria. Based on the 16S rDNA sequence similarity, strains BR4 and BG29 are assigned to the genusHeliobacterium and described as two new species of this genus:Heliobacterium sulfidophilum sp. nov. andHeliobacterium undosum sp. nov. The G+C content of the DNA is 51.3 mol % inHbt. sulfidophilum and 57.2-57.7 mol % inHbt. undosum. The cells ofHbt. sulfidophilum are rods, and the cells ofHbt. undosum are slightly twisted spirilla or short rods. Both new bacteria are motile by peritrichous flagella.Hbt. sulfidophilum produces endospores. The new bacteria are strict anaerobes growing photoheterotrophically on a limited range of organic compounds. In the dark, they can switch from photosynthesis to the slow fermentation of pyruvate. Biotin is required as a growth factor. Both species are highly tolerant to sulfide (up to 2 mM at pH 7.5) and oxidize it photoheterotrophically to elemental sulfur; photoautotrophic growth was not observed. The temperature optimal for growth ofHbt. sulfidophilum andHbt undosum is 30–35‡C, and the optimal pH is 7–8.     

(鼲)属(啮齿目,仓鼠科)同域分布物种形态学鉴别特征组的筛选

现有的分类系统尚缺乏可用于减少䶄属物种种间鉴定不确定性的形态学鉴别特征。鉴于此,本研究旨在筛选出能够对同域分布的棕背䶄（Myodes rufocanus）, 红背䶄（M. rutilus）和堤岸䶄（M. glareolus）进行可靠鉴定的头骨形态指标和方法。为了达到以上目的,本文一方面筛选出能够用于种间鉴别的头骨和齿列形态特征,另一方面提出可用于鉴别以上三个物种的计算公式。对不同研究者提出来用于鉴别以上三个同域分布物种的35个特征进行筛选。头骨形态测量数据的获取需要花费较长的时间,而且结果变异很大。在本研究中,在分析中剔除15个形态特征,20个相对保守的特征被选择用于分析（包括来自头盖骨、牙齿和头骨其它部位的特征）。在20个特征中,有8个特征被选择出来,并使用Statistica 10 计算出判别公式。这些特征使准确鉴定不同个体各自所属种类成为可能。