Succession of mycorrhizal fungi in stands of Pinus sylvestris in the Netherlands

The mycorrhizal mycoflora was investigated in 35 stands of Pinus sylvestris in three types of young (4-13 yr) and three of old (50-80 yr) stands in the Netherlands, differing in number of rotations and soil type. A plot of 1050 m² (30 m x 35 m) within each stand was searched for carpophores during the autumns of 1986 and 1987. 10 soil samples per plot were taken in October 1987 in order to assess the mycorrhizal status of the tree roots. The composition of mycorrhizal mycoflora in the different plots was subjected to TWINSPAN cluster analysis and Detrended Correspondence Analysis. Plot groupings generated by these analyses largely parallelled the stand types, indicating that each stand type has its own mycoflora. Differences in myco-floristic composition between stand types were parallelled by differences in the composition of green vegetation. The young stand types had 3.5–27 x more carpophores and 1.4–6.8 x more species than two of the old stand types One old stand type was intermediate. Considerable differences in species composition between the young stand types were observed. It is concluded that the succession of mycorrhizal fungi is not primarily influenced by ageing of the trees, but rather by changes in the soil. The results were compared with data on changes in the occurrence of fruiting species of mycorrhizal fungi in the Netherlands during this century. It appeared that species which have declined according to these data were more frequent in the young plots than in the old plots. However, these species are reported to be frequent in old stands of P. sylvestris in Estonia and Finland. It is argued that this difference is related to the high nitrogen deposition in the Netherlands.     

Pollen and gene flow in fragmented habitats

Abstract. Habitat fragmentation affects both plants and pollinators. Habitat fragmentation leads to changes in species richness, population number and size, density, and shape, thus to changes in the spatial arrangement of flowers. These changes influence the amount of food for flower-visiting insects and the quantity and quality of pollinations. Seed set in small populations is often reduced and genetic variation is expected but not always found to be low. The majority of studies show that low flower densities have reduced pollination success and higher inbreeding. Density effects are stronger than size effects. Most studies concluded that species richness in flower-visiting insects is directly related to richness in plant species. However, the consequences of low insect species richness for pollination are not always clear, depending on the studied pollinator-plant relationship. The effects of the presence of simultaneously flowering species are highly dependent on the circumstances and may range from competition to facilitation. Other flowering plant species may play a role as stepping stones or corridor in the connection between populations. In the absence of stepping stones even short distances between populations act as strong barriers for gene flow. We illustrate the present review paper with own data collected for three plant species, rare in The Netherlands: Phyteuma spicatum ssp. nigrum (Campanulaceae), Salvia pratensis (Labiatae) and Scabiosa columbaria (Dipsacaceae). The species differ in their breeding systems and in the assemblage of visitor species. Data are shown on the effects of population size on species richness with consequences for seed set. Effects of flower density and isolation on pollen exchange are given. Since plant reproduction depends on the behaviour of individual insects and not on the overall behaviour of the species, the examples all point to individual insects and extrapolate to effects at the species level.     

Topographic complexity and the power to detect structural and functional changes in temperate reef fish assemblages: The need for habitat-independent sample sizes

Functional approaches have shown promising results to detect degradation in marine fish assemblages. However, background variability significantly affects the amplitude of change that is detectable by a monitoring plan, and failing to detect such changes can have devastating consequences and carry aggravated recovery costs due to unnoticed degradation. The present study aimed to understand the relationship between topographic complexity in temperate reefs and the power to detect variations in fish-based metrics. Underwater visual census of fish assemblages was performed using strip transects and a Monte Carlo simulation approach was used to generate a large number of replicates and simulate three alternative hypotheses representing different magnitudes of change. Statistical power to detect differences between null and alternative hypotheses was estimated through 10,000 Mann–Whitney tests for numbers of replicates ranging from 2 to 15. Power tended to vary with topographic complexity particularly with small and medium changes in metric values and when using small sample sizes. While power increased with complexity for most metrics, some showed decreasing trends. With a large effect, 5–15 transects were needed, depending on the metric, to stabilise power above 0.80 independently of habitat features. A power of 0.95, however, could not be achieved for most metrics in all sites, even when using 15 transects. The observation that the power to detect degradation and recovery in temperate reef fish seems to vary with habitat features means that a monitoring programme that is correctly planned for a particular area may not be directly applicable in a nearby reef. Adding to the need to maximise power in monitoring, this study highlights the need to take into account habitat variability in these calculations and estimate habitat-independent sample sizes that are appropriate for the scale and location of interest.     

Reaction of haem containing proteins and enzymes with hydroperoxides: The radical view

The reaction between hydroperoxides and the haem group of proteins and enzymes is important for the function of many enzymes but has also been implicated in a number of pathological conditions where oxygen binding proteins interact with hydrogen peroxide or other peroxides. The haem group in the oxidized Fe³⁺ (ferric) state reacts with hydroperoxides with a formation of the Fe⁴⁺=O (oxoferryl) haem state and a free radical primarily located on the π-system of the haem. The radical is then transferred to an amino acid residue of the protein and undergoes further transfer and transformation processes. The free radicals formed in this reaction are reviewed for a number of proteins and enzymes. Their previously published EPR spectra are analysed in a comparative way. The radicals directly detected in most systems are tyrosyl radicals and the peroxyl radicals formed on tryptophan and possibly cysteine. The locations of the radicals in the proteins have been reported as follows: Tyr133 in soybean leghaemoglobin; αTyr42, αTrp14, βTrp15, βCys93, (αTyr24−αHis20), all in the α- and β-subunits of human haemoglobin; Tyr103, Tyr151 and Trp14 in sperm whale myoglobin; Tyr103, Tyr146 and Trp14 in horse myoglobin; Trp14, Tyr103 and Cys110 in human Mb. The sequence of events leading to radical formation, transformation and transfer, both intra- and intermolecularly, is considered. The free radicals induced by peroxides in the enzymes are reviewed. Those include: lignin peroxidase, cytochrome c peroxidase, cytochrome c oxidase, turnip isoperoxidase 7, bovine catalase, two isoforms of prostaglandin H synthase, Mycobacterium tuberculosis and Synechocystis PCC6803 catalase-peroxidases.     

Changing Estuaries, Changing Views

During the design and the execution of the Delta project, carried out after the storm flood of 1953 in the SW Netherlands, the importance of the long-term effects of morphological and ecological developments driven by tides and currents, have been underestimated. Due to these processes the height of the dams will have to be increased for centuries to come, because the land behind the levees cannot grow in elevation anymore with the rising of the sea. Maintenance of the civil-engineering structures, and mitigating their unpredictable impacts on ecosystems, involve very high recurrent costs. The chance of flooding is reduced, but the potential damage after a storm flood is enlarged: seawalls and dykes provide a false sense of safety against flooding. Changes in the role of agricultural use in the European context, offer an opportunity to abandon arable fields and to retrocede them to the sea in order to absorb tidal energy and to allow the land to rise concomitant with the sea. A cost-benefit analysis of this approach should assess the direct and indirect economic values, as well as the non-use (intrinsic) values, whereby public engagement in management questions, facilitates decision-making processes. Reversible and resilient economic measures within the limits of the natural processes are preferable. A future, speculative perspective is an urbanised landscape, where people and investments are located in safe places, e.g. on floating, or sea-encircled artificial dwelling-mounds, surrounded by a landscape that is ruled by the forces of nature. New approaches such as developed in the Westerschelde offer flexible solutions to flooding problems, and are worth a broader evaluation. A worldwide platform of experts should be organised to study the future management of estuaries and deltas, and to develop and exchange new ideas and techniques.     

中国西南地区水龙骨属植物(水龙骨科)孢子形态研究

利用光学显微镜和扫描电子显微镜对水龙骨属(PolypodiodesCh ing)植物11种(包括1变种)的孢子进行了观察和比较研究。其中,大部分种为首次报道。水龙骨属植物的孢子单裂缝,两侧对称,极面观椭圆形,赤道面观豆形或超半圆形,表面具疣状纹饰,多不具周壁。对光茎水龙骨(P.wattii)和日本水龙骨(P.niponica)、栗柄水龙骨(P.m icrorhizoma)与篦齿蕨(M etapolypodium manm eiense)亲缘关系进行了讨论,为该属植物的系统分类提供了孢粉学方面的证据。根据水龙骨属植物孢粉形态上的证据,水龙骨属植物是一个自然的分类群,赞成秦仁昌1978分类系统的分类处理。     

Long-term spatio-temporal expansion of the native-invasive Retama monosperma on coastal dunes: Importance of land-use and natural dispersal vectors

Expansion of invasive species inducing sands stabilization is becoming an important ecological problem in coastal dunes in some parts of the world. Retama monosperma, an endemic to coasts of SE Spain and NE of Morocco, late-colonizing shrub occurring in sandy coastal areas, was planted along the coast of SW Spain during the 20th century to stabilize dunes. In recent decades, the species has spread rapidly, becoming invasive, and sometimes incurring notable changes in its environment and plant community. The expansion patterns of R. monosperma from 1956 to 2001 were described and quantified at the landscape scale within a protected dune system, using GIS. The differential effects on expansion patterns of the main factor controlling the population spread, grazing by domestic livestock and the abundance of wild rabbits, were analyzed comparatively. R. monosperma displays an exponential, invasive-type expansion trend, presenting a mean annual coverage increase of 15% and a mean lateral spread rate of 65.5 m yr⁻¹ from the original population nucleus to the Western and Eastern ends of the study area. The dispersal activity primarily of rabbits and the absence of competing woody species contribute to this rapid expansion. The highest local increases in plant coverage could be related to increased rabbit abundance and to the improved germination rates of seeds which have passed through the rabbit gut. In contrast, areas highly grazed by livestock present the lowest increases, and an open-type plant community is maintained there for a longer time.     

Expression of integrins α3β1 and α5β1 and GlcNAc β1,6 glycan branching influences metastatic melanoma cell migration on fibronectin

Acquisition of metastatic potential is accompanied by changes in cell surface N-glycosylation. One of the best-studied changes is increased expression of N-acetylglucosaminyltransferase V enzyme (GnT-V) and its products, β1,6-branched N-linked oligosaccharides, observed in the tumorigenesis of many cancers. In this study we demonstrate that during the transition from the vertical growth phase (VGP) (WM793 cell line) to the metastatic stage (WM1205Lu line), β1,6 glycosylation of melanoma cell surface proteins increases as a consequence of elevated expression of the GnT-V-encoding Mgat-5 gene. Treatment with swainsonine led to reduced cell motility on fibronectin in both cell lines; the effect was stronger in metastatic cells, probably due to the higher content of GlcNAc β1,6-branched glycans on the main fibronectin receptors – integrins α5β1 and α3β1. Our results show that GlcNAc β1,6 N-glycosylation of cell surface receptors, which increases with the aggressiveness of melanoma cells, is an important factor influencing melanoma cell migration.     

Paced QRS morphology predicts incident left ventricular systolic dysfunction and atrial fibrillation

Background

The prognostic significance of paced QRS complex morphology on surface ECG remains unclear. This study aimed to assess long-term outcomes associated with variations in the paced QRS complex.