Change in pattern diversity during secondary succession in Estonian forests

Comparisons of observed variance in species diversity (exp LT) and in species richness with expectation assuming a random and independent distribution of species are used to assess the relative importance during succession of niche limitation (Wilson, Gitay & Agnew 1987; limitation of the abundance or occurrence of species by competitive interactions) and nucleation (Yarranton & Morrison 1974; the development of a community through chance establishment or persistence followed by vegetative expansion from those nuclei). Wilson, Gitay & Agnew (1987) and Palmer (1987) suggest a deficit (i.e. lower than expected) in variance of richness is consistent with a ‘niche limitation’ process where competitive sorting makes patches more similar in species number than would be expected. In contrast, variance that is greater than expected is consistent with and could result from underlying environmental heterogeneity (i.e. ‘waterhole effect’). We extend these ideas to suggest that, in addition, a deficit in variance of diversity (expLT) can be interpreted as indicating niche limitation. Further, we suggest that a deficit of variance in richness need not be interpreted as resulting from niche limitation, but could result from limited dispersal and establishment followed by localized spread that causes quadrats to have less compositional overlap than might be expected if species were distributed at random. However, there is little reason to expect that such nucleation would cause a similar reduction in the variance of diversity. First, expLT is relatively insensitive to the presence or absence of rare species, and second, if local competitive processes do restrict the values of exp LT through some form of niche limitation, this could well be independent of the specific species involved. Thus, a combination of lower than expected variance in richness and high variance in diversity suggests nucleation to be important, particularly if the mean pairwise similarity between samples is lower than expected. We first examine a secondary successional sere with stands representing post-logging and mature forest. The variance of diversity is low in the establishment phase, but not in subsequent phases where the tree canopy is well developed. Significantly low variance of species richness is observed in a young forest just entering the thinning phase. Thus, nucleation may be taking place in the establishment phase of forest development, and is almost certainly important in the early thinning phase. Second, we examine communities in the process of equilibration following fertilization, logging, and paludification. All these communities have a low variance in diversity (exp LT) suggesting niche limitation.     

Foliar nutrient concentrations of small Chamaecyparis in Taiwan

Summary Seedlings ofChamaecyparis lawsoniana, C. formosensis andC. taiwanensis were grown in a forest nursery in Taiwan. Native saplings of the latter two species were sampled in a clearcut and in the forest understory. Foliar nutrient concentrations were mostly in the mid-range of values for other conifers. However, Ca (.59–1.5%) and Cu (7–20 ppm) were almost always high. Concentrations of N, P, and K in field saplings in Taiwan were low enough (.7–1.5%, .07–.15%, .47–.60%, respectively) to indicate that these elements are probably limiting growth.Among the three species,C. lawsoniana usually had the lowest foliar nutrient values. When a difference among the species from Taiwan occurred,C. taiwanensis usually was lower. Foliar nutrient concentration varied among provenances, especially withinC. formosensis. Seasonal variability did not occur consistently; nutrients which did change increased their concentrations from the dormant to the growing season, except for K which decreased.     

ELECTRON STAINS : I. Chemical Studies on the Interaction of DNA with Uranyl Salts

Chemical studies have been carried out on the interaction of DNA with uranyl salts. The effect of variations in pH, salt concentration, and structural integrity of the DNA on the stoichiometry of the salt-substrate complex have been investigated. At pH 3.5 DNA interacts with uranyl ions in low concentration yielding a substrate metal ion complex with a UO₂⁺⁺/P mole ratio of about ½ and having a large association constant. At low pH's (about 2.3) the mole ratio decreases to about ⅓. Destruction of the structural integrity of the DNA by heating in HCHO solutions leads to a similar drop in the amount of metal ion bound. Raising the pH above 3.5 leads to an apparent increase in binding as does increasing the concentration of the salt solution. This additional binding has a lower association constant. Under similar conditions DNA binds about seven times more uranyl ion than bovine serum albumin, indicating useful selectivity in staining for electron microscopy.     

Impact of management on biodiversity-biomass relations in Estonian flooded meadows

A negative species richness–productivity relationship is often described in grasslands at smaller scales. We aimed to study the effect of management on this relationship. In particular, we addressed the relative importance of biomass cutting, hay removal and nutrient impoverishment on species richness and growth form structure. We conducted fieldwork in flooded meadows in Alam-Pedja Nature Reserve, central Estonia. We sampled vegetation in managed and abandoned stands of two types of alluvial meadows, sedge and tall forb meadow. Aboveground biomass and litter were harvested, weighed and analysed for major plant nutrients by near infrared reflectance spectroscopy. Three groups of general additive models were developed and compared, addressing the impact of (i) productivity, (ii) nutrients and (iii) management regime on species richness. Management—mowing and hay removal—reduced the amount of litter but not aboveground biomass. Management led to a decrease in nitrogen in the biomass and enhanced species richness, particularly in the tall forb meadow. The strongest determinant of species richness was the amount of litter, exhibiting a hump-shaped relationship with richness. The effect of nitrogen supply was significant, but explained less variation. Management increased the proportion of sedges in the sedge meadow and of small herbs in the tall forb meadow. We conclude that litter removal is the most important management means to support biodiversity. On highly productive sites, reducing nutrients via hay removal is of secondary importance within a timeframe of 10 years.     

Population-level performance of Arabidopsis thaliana (L.) Heynh in dense monocultures

尽管几乎所有的农业物种在育种过程中都经历了从多物种环境向密集单种农田的过渡,但对非农业植物物种在单一栽培条件下的表现知之甚少。鉴于最近的研究成果突出杂草物种拟南芥为作物育种提供新视角的可能性,本研究的目的是了解播种密度对拟南芥在不同光周期环境下群体和个体表现的影响。我们研究了拟南芥Cvi-0生态型的表现。Cvi-0的选择基于一项初步实验,发现Cvi-0生态型植物表现出强烈的竞争性能。播种密度处理设置为每株17.6、8.8、4.4、2.2和1.1 cm²,光周期环境为日照12小时或16小时。结果表明,植物在所有密度处理下均获得了恒定的总种子产量。播种密度和日照时间处理会有一些相互作用：在高播种密度和长日照时间的处理下,种子重量更大,而日照时间短的处理下种子重量与密度呈负相关。这些结果阐明了一年生植物在面对激烈的种内竞争时能够采取不同的策略,并有助于为提高群体表现的作物育种提供新的前景。     

Flight metabolic rate has contrasting effects on dispersal in the two sexes of the Glanville fritillary butterfly

Evolution of dispersal is affected by context-specific costs and benefits. One example is sex-biased dispersal in mammals and birds. While many such patterns have been described, the underlying mechanisms are poorly understood. Here, we study genetic and phenotypic traits that affect butterfly flight capacity and examine how these traits are related to dispersal in male and female Glanville fritillary butterflies (Melitaea cinxia). We performed two mark–recapture experiments to examine the associations of individuals’ peak flight metabolic rate (MR_peak) and Pgi genotype with their dispersal in the field. In a third experiment, we studied tethered flight in the laboratory. MR_peak was negatively correlated with dispersal distance in males but the trend was positive in females, and the interaction between MR_peak and sex was significant for long-distance dispersal. A similar but nonsignificant trend was found in relation to molecular variation at Pgi, which encodes a glycolytic enzyme: the genotype associated with high MR_peak tended to be less dispersive in males but more dispersive in females. The same pattern was repeated in the tethered flight experiment: the relationship between MR_peak and flight duration was positive in females but negative in males. These results suggest that females with high flight capacity are superior in among-population dispersal, which facilitates the spatial spreading of their reproductive effort. In contrast, males with high flight capacity may express territorial behaviour, and thereby increase the number of matings, whereas inferior males may be forced to disperse. Thus, flight capacity has opposite associations with dispersal rate in the two sexes.     

Imidazo[1,2-a]pyridines with potent activity against herpesviruses

Synthesis of a series of 2-aryl-3-pyrimidyl-imidazo[1,2-a]pyridines with potent activity against herpes simplex viruses is described. Synthetic approaches allowing for variation of the 2-aryl, 3-heteroaryl as well as other imidazopyridine substituents are outlined and resulting effects on antiviral activity are highlighted. Several compounds with in vitro antiviral activity similar or better than acyclovir are described.     

Climate Warming May Facilitate Invasion of the Exotic Shrub Lantana camara

Plant species show different responses to the elevated temperatures that are resulting from global climate change, depending on their ecological and physiological characteristics. The highly invasive shrub Lantana camara occurs between the latitudes of 35°N and 35°S. According to current and future climate scenarios predicted by the CLIMEX model, climatically suitable areas for L. camara are projected to contract globally, despite expansions in some areas. The objective of this study was to test those predictions, using a pot experiment in which branch cuttings were grown at three different temperatures (22°C, 26°C and 30°C). We hypothesized that warming would facilitate the invasiveness of L. camara. In response to rising temperatures, the total biomass of L. camara did increase. Plants allocated more biomass to stems and enlarged their leaves more at 26°C and 30°C, which promoted light capture and assimilation. They did not appear to be stressed by higher temperatures, in fact photosynthesis and assimilation were enhanced. Using lettuce (Lactuca sativa) as a receptor plant in a bioassay experiment, we also tested the phytotoxicity of L. camara leachate at different temperatures. All aqueous extracts from fresh leaves significantly inhibited the germination and seedling growth of lettuce, and the allelopathic effects became stronger with increasing temperature. Our results provide key evidence that elevated temperature led to significant increases in growth along with physiological and allelopathic effects, which together indicate that global warming facilitates the invasion of L. camara.     

Glial cells

The nervous system is built from two broad categories of cells, neurones and glial cells. The glial cells outnumber the neurones and the two cell types occupy a comparable amount of space in nervous tissue. The main glial cell types are, in the central nervous system, astrocytes and oligodendrocytes and, in the peripheral nervous system, Schwann cells, enteric glial cells and satellite cells. In the embryo, glial cells form a cellular framework that permits the development of the rest of the nervous system, and regulate neuronal survival and differentiation. The best known function of glia in the adult is the formation of myelin sheaths around axons thus allowing the fast conduction of signalling essential for nervous system function. Glia also maintain appropriate concentrations of ions and neurotransmitters in the neuronal environment. Increasing body of evidence indicates that glial cells are essential regulators of the formation, maintenance and function of synapses, the key functional unit of the nervous system.