Spatial distribution and morphologic diversity of virioplankton in Lake Donghu, China

The spatial distribution and morphological diversity of virioplankton were determined in Lake Donghu which contains three trophic regions: hypertrophic, eutrophic and mesotrophic region. Virioplankton abundance measured by transmission electron microscope (TEM) ranged from 7.7 × 10⁸ to 3.0 × 10⁹ ml^–1, being among the highest observed in any natural aquatic system examined so far. The spatial distribution of virioplankton was correlated significantly with chlorophyll a concentration (r = 0.847; P < 0.01) at the sampling sites in Lake Donghu. 76 morphotypes were observed. Most morphotypes have tails, belonging to Siphoviridae, Myoviridae and Podoviridae. The majority of tailed phages in the lake were Myoviridae. Morphotypes which were rarely reported, such as prolate-headed virus-like particles, lemon-shaped virus-like particle, and viruses resembling Tectiviridae and Corticoviridae were all observed in the lake. It is concluded that the high viral abundance might be associated with high density of phytoplankton including algae and cyanobacteria. There was high viral diversity in this eutrophic shallow lake. In addition, cyanophage represented an important fraction of the virioplankton community in Lake Donghu.     

Identification of PaPKS1, a polyketide synthase involved in melanin formation and its use as a genetic tool in Podospora anserina

In the filamentous fungus Podospora anserina, many pigmentation mutations map to the median region of the complex locus ‘14’, called segment ‘29’. The data presented in this paper show that segment 29 corresponds to a gene encoding a polyketide synthase, designated PaPKS1, and identifies two mutations that completely or partially abolish the activity of the PaPKS1 polypeptide. We present evidence that the P. anserina green pigment is a (DHN)-melanin. Using the powerful genetic system of PaPKS1 cloning, we demonstrate that in P. anserina trans-duplicated sequences are subject to the RIP process as previously demonstrated for the cis-duplicated regions.     

The effect of grazing on granivory patterns in the temperate Monte Desert, Argentina

Structural variations result in a marked heterogeneity of processes in arid environments. Disturbances have noticeable impacts on ecosystems, and a solid way of assessing their effect is to analyze how ecological processes operate. In deserts, granivory has been considered as a keystone process. The objective of our study was to determine the effect of domestic grazing on seed removal rates by birds, ants and rodents as an indirect measure of the process of granivory. This study was carried out in grazed and ungrazed habitats in the central Monte desert ecoregion in Argentina, during February and July 2002. We analyzed three major habitats: mesquite forest, creosotebush shrubland, and sand dunes under two different treatments (grazed, ungrazed). We found significant effects of grazing and non-grazing treatments on total seed removal rates, among granivorous taxa, as well as interactions with season and habitats. Ants and birds were the taxa that differed most under grazing pressure whereas seed removal by rodents showed no significant responses towards grazing. In conclusion, grazing affects plant structure and the assemblage of granivorous taxa, which in turn translates to the granivory process, adding another source of variation to the seed removal patterns reported for the temperate Monte desert.     

Seed bank assembly in an unmanaged ruderal grassland recovering from long-term exposure to industrial emissions

The main aim of this 3-year study was to relate the temporal patterns in seed bank composition of a ruderal grassland previously subjected to industrial pollution with the successional patterns in the above-ground vegetation. In particular, we tested whether the observed changes conformed to a paradigm of declining seed numbers and diversity and decreasing similarity between seed bank and vegetation, as previously formulated for secondary successions. We found that seed numbers and the number of species per soil sample increased during the 3 years of the study. The compositional similarity between seed bank and vegetation did increase for the 0–2 cm surface layer, and remained roughly constant for deeper soil layers. Thus, the patterns found differed from those of other secondary successional communities and do not support the tested paradigm. Rather, our findings resemble those from a number of primary successional ecosystems. We suggest that temporal patterns of similarity between seed bank and vegetation should be interpreted in terms of the factors that determine the relative rates of compositional change in vegetation and seed bank at different stages of succession. Our study also provides information about the seed bank persistence of 22 species, including several species for which such knowledge previously was scarce. In particular, this study indicates the extreme longevity of the seeds of the halophytic grass Puccinellia distans. Several years after its rapid decline in the vegetation, this species dominated the seed bank, and no measurable decline in seed density was detected during this study.     

Phenotypic plasticity of invasive Alternanthera philoxeroides in relation to different water availability, compared to its native congener

Phenotypic plasticity and genetic differentiation are two possible mechanisms that plants use to cope with varying environments. Although alligator weed (Alternanthera philoxeroides) possesses very low genetic diversity, this alien weed has successfully invaded diverse habitats with considerably varying water availability (from swamps to dry lands) in China. In contrast, its native congener (Alternanthera sessilis) has a much narrower ecological breadth, and is usually found in moist habitats. To understand the mechanisms underlying the contrasting pattern, we performed a greenhouse experiment to compare the reaction norms of alligator weed with those of its native congener, in which water availability was manipulated. Our results revealed that the two congeners had similar direction of phenotypic plasticity. However, A. philoxeroides showed greater plasticity in amount than did A. sessilis in many traits examined during the switch from wet to drought treatment. Nearly all of the phenotypic variance in A. philoxeroides could be ascribed to plasticity, while A. sessilis had a much higher fraction of phenotypic variance that could be explained by genotypic variation. These interspecific differences in plastic responses to variable water availability partially explained the difference in spatial distribution of the two congeners.     

Indications for a humid climate in the Western Desert of Egypt 11–10 Myr ago: evidence from Galagidae (Primates, Mammalia)

The timing of desertification of the Sahara Desert is poorly understood, with recent estimates indicating an onset of hyper-aridity during the Latest Miocene. Field work in Egypt in 2005 has led to the discovery of evidence that indicates that 11–10 Ma the Western Desert was covered in woodland. Fossiliferous cave breccia at Sheikh Abdallah, Western Desert, Egypt, has yielded a Late Miocene (11–10 Ma) microvertebrate fauna, which contains Galagidae, Microchiroptera, Macroscelididae, Soricidae, Erinaceidae, and Rodentia. The locality also yielded the remains of frogs, snakes, lizards, and birds. The fauna indicates a mean annual rainfall in excess of 500 mm and perhaps as much as 1,200 mm. This palaeoclimatic information is important because it reveals that the Sahara Desert, which is today the largest in the world, was either considerably smaller during the Late Miocene than it is today, or that it did not yet exist as a continuous hyper-arid belt right across the continent. This data accords with estimates of a Latest Miocene (8–7 Ma) increase in aridity in the Sahara. To cite this article: M. Pickford et al., C. R. Palevol 5 (2006).     

Ant diversity and its relationship with vegetation and soil factors in an alluvial fan of the Tehuacán Valley, Mexico

In this study, we analyze the ant community found along an alluvial fan located in the Tehuacán Valley, central Mexico. Considering that this fan is composed of four terraces with different soils and vegetation structures, our main goal was to determine whether there are significant differences in ant diversity among terraces. To accomplish this goal, we determine species richness and abundance in order to calculate diversity and evenness indices. In addition, we classify species in different feeding guilds to evaluate whether differences among terraces exist. We expected higher ant diversity and variety of food guilds in terraces with sandy soils and complex vegetation structures than in terraces with argillic and calcic horizons. Correlations between several diversity parameters, and soil percent-sand and vegetation structure were also conducted. A total of 26 ant species were recorded along the fan. Species richness was not different among terraces whereas abundance was higher in sandy soils and on terraces with complex vegetation structure. Particularly, the abundance of the harvester ant Pogonomyrmex barbatus was higher in these terraces decreasing total ant diversity and evenness. Species richness within feeding guilds was similar among terraces with the generalized foragers as the most common. Our work suggests that percentage of sand in the soil and complexity of vegetation structure of the alluvial fan studied might be influencing ant distribution and favoring the abundance of numerically dominant species which could be affecting the diversity patterns of the whole community.     

Photon emissions from rice cells elicited by N-acetylchitooligosaccharide are generated through phospholipid signaling in close association with the production of reactive oxygen species

Biophotons are ultraweak light emissions from biochemical reactions in a living body. They increase in suspension-cultured rice (Oryza sativa L.) cells when elicited by N-acetylchitooligosaccharide. Biochemical analyses were undertaken to investigate the relationship between disease response and biophotons in order to clarify the emission mechanism of biophotons caused by this elicitor. Photon emissions induced by N-acetylchitohexaose were suppressed when cells were pretreated with the reactive oxygen species (ROS)-generating inhibitors: pyrocatechol-3,5-disulfonic acid disodium salt (Tiron); diphenylene iodonium (DPI); and salicylhydroxamic acid (SHAM). Conversely, exogenously applied ROS (superoxide and hydrogen peroxide) were able to induce photon emissions. The effects of protein phosphorylation (K-252a) and the Ca(2+) signaling inhibitors, ethylene glycol-bis(beta-aminoethylether)-N,N,N',N'-tetraacetic acid (EGTA) and LaCl(3), caused photon emissions to decrease. It is clear that photon emissions from rice cells elicited by N-acetylchitohexaose are closely associated with the ROS-generating system, and are regulated by Ca(2+) signaling and protein phosphorylation. Exogenously applied phosphatidic acid (PA), the second messenger in the signal transduction of disease response, raised photon emissions in rice cells. Comparisons of photon emissions from PA and N-acetylchitohexaose regarding time courses, spectral compositions, and the inhibition ratios of several inhibitors, as well as a loss- and gain-of-function assay using the protein synthesis inhibitor cycloheximide (CHX) and PA, showed the possibility that photon emissions from rice cells elicited by N-acetylchitooligosaccharide were generated through PA, an intermediate of phospholipid signaling.     

Transgenic tobacco (Nicotiana tabacum L. cv. Samsun-NN) plants over-expressing a synthetic HRP-C gene are altered in growth, development and susceptibility to abiotic stress

The physiological role of class III peroxidases (EC 1.11.1.7) in controlling plant growth and development has been investigated by over-expression of both native and heterologous peroxidases. However, it has remained an enigma as to why the phenotypes of different peroxidase over-expressing transgenics vary. In order to resolve the conflicting information about the consequences of peroxidase over-expression, we have explored the role of the subcellular targeting of HRP-C in controlling stem growth, root development, axillary branching and abiotic stress tolerance in tobacco (Nicotiana tabacum L.). Altering the sub-cellular targeting of vacuolar HRP-C, such that over-expressed peroxidase accumulates in the cytoplasm and cell wall, induced phenotypic changes that are typically associated with altered auxin homeostasis, and over-expression of cell wall located peroxidases. We conclude that sub-cellular targeting is a determinant of the phenotype of peroxidase over-expressing plants.     

Incompatibility and pollen competition in Alnus glutinosa: Evidence from pollination experiments

Different types of incompatibility systems were found to operate simultaneously in alnus glutinosa in the course of numerous pollination experiments, including self-pollination and pollination with controlled pollen mixtures. Isozyme genetic markers were used to identify the pollen parent of each offspring from the mixed pollination experiments, thus allowing specification of the fertilization success of each pollen parent. In a first step, these results were compared with observations on in vitro pollen germination experiments. This comparison allows for exploration of the explanatory value of different germination media as models of germination conditions on stigmas. In most cases, the data suggest that the in vitro germination conditions resemble the fertilization conditions in vivo, at least in the sense that they favor the same pollen parents. By providing a generic and operable definition of the two basic types of incompatibility, eliminating (inability to fertilize ovules) and cryptic (resulting in lowered fertilization success of a pollen parent under competition), evidence was detected for the existence of both types of incompatibility in alnus glutinosa, where eliminating incompatibility occurred as self-incompatibility only. However, since this incompatibility seems to act primarily via pollen elimination, seed production is not likely to be negatively affected in natural populations, even for comparatively large amounts of self-pollination. This revised version was published online in July 2006 with corrections to the Cover Date.     

Cyanobacteria and Cyanobacterial Lichens from Inselbergs of the Ivory Coast,Africa

This study focuses on the saxicolous lichens and cyanobacteria of the open, exposed rock surface of inselbergs. Twenty-three species of cyanobacteria and 17 cyanobacterial lichen species (“cyanolichens”) from several inselbergs and other rocky outcrops of three major climatic regions, savanna, transition zone and rain forest, are reported from the Ivory Coast. Inselbergs are isolated and frequently mountains consisting of Precambrian granites or gneisses that abruptly rise from the surrounding plains. Cyanobacteria were found to be the dominating organisms on all rock surfaces. The lichens found mainly belong to the family Peltulaceae and a few were present from the family Lichinaceae. Nine species of the cyanolichens and most of the cyanobacteria are new for the Ivory Coast. A gradient in total species number (cyanolichens and cyanobacteria) occurs from the savanna to the rain forest, with a decrease in species number towards the rain forest. Saxicolous cyanobacterial lichens reached a higher species number in the savanna type ecosystem (11) than on inselbergs in the rain forest (7). The cyanolichens and cyanobacteria found are characteristic for larger, light-exposed rock surfaces and species like P. congregate, P. lingulata, P. tortuosa and P. umbilicata preferentially occur on the granite or sandstone of inselbergs.     

Cationized starch-based material as a new ion-exchanger adsorbent for the removal of C.I. Acid Blue 25 from aqueous solutions

This article describes the use of a cationized starch-based material as new ion-exchanger adsorbent for the removal of C.I. Acid Blue 25 (AB 25) from aqueous solutions. Batch adsorption studies concerning the effects of contact time, pH and temperature are presented and discussed. Adsorption experimental data showed that: (i) the process was uniform and rapid: adsorption of dye reached equilibrium in 50 min in the wide pH range of dye solutions; (ii) adsorption kinetics followed the pseudo-second order model; (iii) the Langmuir model yielded a much better fit than the Freundlich model for the dye concentration range under study; (iv) this adsorbent exhibited interesting adsorption capacities: on the basis of the Langmuir analysis, the maximum adsorption capacity was determined to be 322 mg of dye per gram of material at 25 degrees C; (v) the adsorption capacity decreased with increasing temperature; and (vi) the negative value of free energy change indicated the spontaneous nature of adsorption.     

The fauna and associated artefacts from the Lower Pleistocene site of Mansourah (Constantine, Algeria)

The site of Mansourah (Constantine, Algeria) had yielded to the early authors, and more recently to the late G. Laplace, a lithic industry associated with a fauna of large Mammals, which looks contemporaneous with that of Aïn Hanech, although it is well-distinct ecologically, and might even be slightly older. The lithic assemblage is completely devoid of any bifacial artefact or cleaver and can only be referred to the Oldowan. Thus, the Mansourah site documents a very early human occupation of North Africa, and perhaps one of the earliest. To cite this article: Y. Chaid-Saoudi et al., C. R. Palevol 5 (2006).     

Use of regression analysis in plant cell,tissue, and organ culture experiments

Several authors have suggested that plant biotechnologists perform regression or trend analysis to compare means of related quantitative treatments (e.g., doses of inositol). The present paper compares two statistical strategies to determine the effect of inositol (0–400 mg l⁻¹) on proteolytic activity in the culture medium during pineapple growth in temporary immersion bioreactors. Strategy 1 involved one-way analysis of variance (ANOVA) followed by Tukey’s Honestly Significant Difference (HSD). Strategy 2 consisted in the development of different regression analyses to determine the best fit equations to describe the experimental results. Curvefit software (version 2.10-0, May 15, 1987, Thomas S. Cox) was used. Cauchy, Normal, Parabola, and Hoerl equations were the best fitted according to their determination coefficients (R ²). The optimal inositol concentrations to increase proteolytic activity were determined from the equations. Quite different results were obtained following strategy 2: 126.76 mg l⁻¹ inositol from Cauchy, 131.29 mg l⁻¹ from Normal, 145.06 mg l⁻¹ from Parabola, and 14.05 mg l⁻¹ from Hoerl equations. In contrast, experimental data identified 200 mg l⁻¹ inositol as the most adequate concentration to increase proteolytic activity in the culture medium. The statistical strategy 1, one-way ANOVA followed by Tukey HSD clearly supported this biological observation. In this paper, regression analysis was not useful to describe our experimental results.     

Long-term ecosystem level experiments at Toolik Lake, Alaska, and at Abisko, Northern Sweden: generalizations and differences in ecosystem and plant type responses to global change

Long‐term ecosystem‐level experiments, in which the environment is manipulated in a controlled manner, are important tools to predict the responses of ecosystem functioning and composition to future global change. We present the results of a meta‐analysis performed on the results of long‐term ecosystem‐level experiments near Toolik Lake, Alaska, and Abisko, Sweden. We quantified aboveground biomass responses of different arctic and subarctic ecosystems to experimental fertilization, warming and shading. We not only analysed the general patterns but also the differences in responsiveness between sites and regions. Aboveground plant biomass showed a broad similarity of responses in both locations, and also showed some important differences. In both locations, aboveground plant biomass, particularly the biomass of deciduous and graminoid plants, responded most strongly to nutrient addition. The biomass of mosses and lichens decreased in both locations as the biomass of vascular plants increased. An important difference between the two regions was the smaller positive aboveground biomass response of deciduous shrubs in Abisko as compared with Toolik Lake. Whereas in Toolik Lake Betula nana increased its dominance and replaced many of the other plant types, in Abisko all vascular plant types increased in abundance without major shifts in relative abundance. The differences between the responses of the dominant vegetation types of the Toolik Lake region, i.e. tussock tundra systems, and that of the Abisko region, i.e. heath systems, may have important implications for ecosystem development under expected patterns of global change. However, there were also large site‐specific differences within each region. Several potential mechanistic explanations for the differences between sites and regions are discussed. The response patterns show the need for analyses of joint data sets from many regions and sites, in order to uncover common responses to changes in climate across large arctic regions from regional or local responses.     

Competition intensity and its importance: results of field experiments with<Emphasis Type="Italic"> Anthoxanthum odoratum</Emphasis>

The effect of community productivity on competition was studied in 82 permanent plots using two removal experiments with the rhizomatous perennial grass Anthoxanthum odoratum. The removal of neighbouring plants had a positive effect on the number of shoots and total above-ground biomass of Anthoxanthum but no significant effect on mean shoot biomass. The relative competition intensity coefficient (RCI) calculated from these data showed that competition intensity increased with increasing community productivity. Similarly, the importance of competition and the difference between local maximum and local average population density increased with increasing community productivity. We concluded that for Anthoxanthum the impact of competition is greater in high-productivity areas and that competition reduces population density. No evidence was found supporting the importance of positive interactions between plants in tundra areas. Received: 22 June 1999 / Accepted: 3 April 2000     

Evidence for a nutritional disorder of Oxalis acetosella L. on acid forest soils; II. Diagnostic field experiments and nutrient solution studies

Different field experiments were performed to discover the main factor(s) responsible for the poor leaf growth, moderate propagation and leaf chlorosis of Oxalis acetosella in an old Norway spruce stand with acid soil (Höglwald Forest). A previous study had suggested, that Ca (or Mg) deficiency or Mn toxicity could be involved.In a Main Diagnostic Field Experiment with an intact population, Ca and Mg were either applied as sulphate or carbonate to distinguish between nutritional and pH effects. Mn and Si were also applied to aggravate or overcome possible effects of Mn toxicity. Enhancement experiments with different amounts of CaSO₄ were conducted to investigate the Ca dose-effect relationship under field conditions. Additional trials with SrCO₃, BaCO₃ and NaHCO₃ had the goal to raise the soil pH without supply of nutrients.Greenhouse experiments with Oxalis acetosella supplemented the field studies by investigating the Ca and Mn dose-effect relationships under controlled conditions. Growth, vitality and nutrition of Oxalis were studied in a nutrient solution culture at pH 4.0 over a range of concentrations of Ca (20 to 5000 mol L_-1) and Mn (5 to 1000 mol L_-1) respectively. Furthermore, the effects of two contrasting ammonium/nitrate ratios were tested. The nutritional composition of the basal nutrient solution and the microclimate in the greenhouse were as far as possible adjusted to the environmental conditions of the plant in the Höglwald Forest.All these studies led to the conclusion, that the moderate growth and vitality of Oxalis in the Höglwald Forest was mainly due to an insufficient Ca supply, rather than an effect of Mg deficiency, low soil pH or Mn toxicity. The application of CaSO₄ caused a similar stimulation of the growth as CaCO₃. A clearly positive, close CaSO₄ dose-effect relationship was detected in field experiments as well as in the nutrient solution study. The same type of leaf chloroses as in the field was reproduced through low Ca nutrient solutions. Predominant ammonium nutrition may significantly impair Ca uptake.Oxalis acetosella displayed a relatively high leaf tissue tolerance of excessive Mn. There was no indication for a Mn-induced Ca deficiency in the Höglwald Forest. Enhanced Si uptake led to a partial vitalization of Oxalis; the reason for that remained unclear.     

Influence of temperature,oxygen and food availability on the migrational activity of bathyal benthic foraminifera: evidence by microcosm experiments

Foraminifera are a dominant group of amoeboid protists in the deep-sea and play possibly a significant role in decomposition processes of incoming organic matter. In order to study the poorly known ecology of these protozoans, microcosm experiments with living bathyal benthic foraminifera have been conducted. Foraminifera from 2880 m and shallower water depths were successfully maintained and their movement patterns investigated. By video documentation, high mean migration speed of 20,02 (N = 22) and 24,48 m min^-1 (N = 10) at 4 °C were found for species such as Hoeglundina elegans and Quinqueloculina seminula from 1847 m and 1921 m water depth, respectively. The results demonstrate that some bathyal foraminifera have migration speeds comparable to those of shallow water species. Environmental factors such as temperature, food concentration and oxygen content showed a marked influence on the migration of some species. An increase in temperature from 10 °C to 15 °C resulted in an increase of 35% in the migration speed of Allogromia spp. However, other species reacted differently. Higher food concentration resulted in a decrease in speed of some species. While in Quinqueloculina lamarckiana speed was not greatly affected by a low oxygen content in the sediment, other foraminifera responded to oxygen depletion by migration to the surface layers. Observations of benthic foraminifera in the laboratory microcosms are discussed in relation to microhabitats and the fate of organic matter on the sea floor and in the sediment.