bluuebunny/crossref_metadata_2025_split huggingface dataset:
Hepatitis B virus‐induced defect of monocyte‐derived dendritic cells leads to impaired T helper type 1 response in vitro: mechanisms for viral immune escape
Authors: Beckebaum Susanne , Cicinnati Vito R. , Zhang Xia , Ferencik Stanislav , Frilling Andrea , Grosse‐Wilde Hans , Broelsch Christoph Erich , Gerken Guido 
Published: July 2003

SummaryDendritic cells (DC) are the most potent antigen‐presenting cells and play a central role in the induction of antiviral immune responses. Recently, we have shown that monocyte‐derived DC (MoDC) from patients with chronic hepatitis B virus (HBV) infection are functionally impaired. In our present study MoDC from healthy subjects were propagated in vitro and inoculated with HBV particles to investigate the precise mechanisms that underly MoDC dysfunction. T‐cell proliferation assays revealed an impaired allostimulatory capacity of HBV‐inoculated MoDC (HBV‐MoDC) as well as a lower potential of stimulating autologous T cells against a recall antigen in comparison to control‐MoDC. Interleukin‐2, tumour necrosis factor‐α and interferon‐γ production by T cells in proliferation assays with HBV‐MoDC was significantly lower than with control‐MoDC and correlated with lower IL‐12 production in HBV‐MoDC cultures. The presence of the nucleoside analogue lamivudine (3TC), an inhibitor of HBV replication, restored impaired allostimulatory function of HBV‐MoDC and up‐regulated major histocompatibility complex class II expression. These results show that HBV infection compromises the antigen‐presenting function of MoDC with concomitant impairment of T helper cell type 1 responses. This may play an important role for viral immune escape leading to chronic HBV infection. However, 3TC treatment can overcome HBV‐MoDC‐related T‐cell hyporeactivity and this underscores its important role in enhanced immune responses to HBV.
Human secretory immunoglobulin A may contribute to biofilm formation in the gut
Authors: Randal Bollinger R. , Everett Mary Lou , Palestrant Daniel , Love Stephanie D. , Lin Shu S. , Parker William 
Published: July 2003

SummaryIt is critical, both for the host and for the long‐term benefit of the bacteria that colonize the gut, that bacterial overgrowth with subsequent bacterial translocation, which may lead to sepsis and death of the host, be avoided. Secretory IgA (sIgA) is known to be a key factor in this process, agglutinating bacteria and preventing their translocation in a process termed ‘immune exclusion’. To determine whether human sIgA might facilitate the growth of normal enteric bacteria under some conditions, the growth of human enteric bacteria on cultured, fixed human epithelial cells was evaluated in the presence of sIgA or various other proteins. Human sIgA was found to facilitate biofilm formation by normal human gut flora and by Escherichia coli on cultured human epithelial cell surfaces under conditions in which non‐adherent bacteria were repeatedly washed away. In addition, the presence of sIgA resulted in a 64% increase in adherence of E. coli to live cultured epithelial cells over a 45‐min period. Mucin, another defence factor thought to play a key role in immune exclusion, was found to facilitate biofilm formation by E. coli. Our findings suggest that sIgA may contribute to biofilm formation in the gut.
Effects of population size and genetic variation on the response of Succisa pratensis to eutrophication and acidification
Authors: Vergeer Philippine , Rengelink Ramses , Ouborg N. Joop , Roelofs Jan G. M. 
Published: July 2003

Summary

Succisa pratensis, a characteristic plant species of biodiverse, slightly acidic grasslands (NARDETEA), has declined in the Netherlands over recent decades. This process has mainly been attributed to environmental stress caused by anthropogenic acidification and eutrophication, although genetic deterioration and decreasing population size may also be involved.
We analysed the combined effects of environmental stress, genetic variation and population size on the performance of Succisa pratensis.
Individual plant performance was negatively affected by eutrophication and, to a smaller extent, by acidification. Plants originating from smaller populations performed less well and showed less genetic variation and higher inbreeding coefficients than plants from large populations. Strong interactions between population size and stress treatments reflected the fact that plants from small populations suffered more from deteriorating soil conditions than those from large populations.
abitat fragmentation may reinforce the negative effects of environmental stress, leading to even the less effective treatment (acidification) having serious consequences.
Community assembly along proglacial chronosequences in the high Arctic: vegetation and soil development in north‐west Svalbard
Authors: Hodkinson Ian D. , Coulson Stephen J. , Webb Nigel R. 
Published: July 2003

Summary

Community assembly is described for two contrasting high Arctic chronosequences representing glacial regression of up to 2000 years on Svalbard. The chronosequences included a nutrient‐poor glacier foreland (Midtre Lovénbre) and a series of nutrient‐enriched islands (Lovén Islands) progressively released from below a tidewater glacier.
Soil development and community assembly paralleled proglacial sequences elsewhere but time scales were extended and mature vegetation types comprised species‐poor prostrate communities.
Initial colonization by Cyanobacteria stabilized soil surfaces and raised nutrient status. Cyanobacteria formed the dominant ground cover (up to 34%) for 60 years, after when they declined.
Vascular plants established slowly and represented minor components of ground cover for the first 100 years. Earliest colonizers were often species with ectomycorrhizal associations, followed by mid‐successional species that tended to disappear as ground cover increased. Some species present in the mature vegetation at the oldest sites, established only after 60+ years.
Species richness of vascular plants increased for c. 100 years, beyond when only occasional species were added. Bryophytes became increasingly dominant with time.
Soil development on the Midtre Lovénbre and Lovén Island chronosequences was similar after 100 years. Differences subsequently developed, with organic horizon depth, percentage organic matter and water content on the older Lovén islands significantly greater than at equivalent Midtre Lovénbre sites. This was associated with increased bryophyte cover but lower vascular plant species richness. One explanation is a slightly more favourable microclimate, coupled with nutrient input from nesting birds.
Communities progressively recruit from a limited pool of effectively dispersed species, each with particular ecological requirements that determine their point of entry into the community. A measure of determinism by default is suggested in the way communities assembled.
Under climate warming, in the absence of nutrient enrichment, community development will accelerate but will be constrained by nutrient limitations and a restricted species pool. Where nutrients are less limiting, acceleration towards a moss‐dominated community is expected, with a lower species richness of vascular plants.
Floral neighbourhoods in the sea: how floral density, opportunity for outcrossing and population fragmentation affect seed set in Zostera marina
Authors: Reusch Thorsten B. H. 
Published: July 2003

Summary

Almost nothing is known about how the floral neighbourhood affects reproductive output in plants with subaqueous pollination (hydrophily), such as seagrasses, an ecologically important group of some 60 marine angiosperms.
I studied how floral density, genetic diversity and population fragmentation affect seed set in Zostera marina (eelgrass), a functionally hermaphrodite seagrass with extensive clonal propagation.
In a field experiment in the south‐western Baltic Sea, I increased or decreased the density of flowering shoots in 6 × 6 m plots. Early seed set was a positive, saturation‐type function of density suggesting pollen limitation below approximately 5 flowering shoots m−2.
Using molecular markers, I determined local genotypic diversity and outcrossing rates as indicators of outcrossing opportunities. I found only non‐significant effects of these variables on early seed set, suggesting that density of the floral neighbourhood is more important than genetic composition.
Early seed set was 22% lower in isolated vegetation patches compared to continuous eelgrass meadow (> 50 m2).
Given the spatial scale of the observed pollen limitation, and low natural densities of flowering shoots in the field, pollen limitation may be widespread in Z. marina and, possibly, other plant species with subaqueous pollination.
Luxury consumption of soil nutrients: a possible competitive strategy in above‐ground and below‐ground biomass allocation and root morphology for slow‐growing arctic vegetation?
Authors: Van Wijk M. T. , Williams M. , Gough L. , Hobbie S. E. , Shaver G. R. 
Published: July 2003

Summary

A field‐experiment was used to determine how plant species might retain dominance in an arctic ecosystem receiving added nutrients. We both measured and modelled the above‐ground and below‐ground biomass allocation and root morphology of non‐acidic tussock tundra near Toolik Lake, Alaska, after 4 years of fertilization with nitrogen and phosphorus.
Compared with control plots, the fertilized plots showed significant increases in overall root weight ratio, and root biomass, root length and root nitrogen concentration in the upper soil layers. There was a strong trend towards relatively more biomass below ground.
We constructed an individual teleonomic (i.e. optimality) plant allocation and growth model, and a competition model in which two plants grow and compete for the limiting resources.
The individual plant model predicted a strong decrease in root weight ratio with increased nutrient availability, contrary to the results obtained in the field.
The increased investment in roots in the fertilized plots found in the field could be explained in the competition model in terms of luxury consumption of nutrients (i.e. the absorbance of nutrients in excess of the immediate plant growth requirements). For slow‐growing species with relatively low phenological and physiological plasticity it can be advantageous to increase relative investment into root growth and root activity. This increased investment can limit nutrient availability to other fast‐growing species and, thereby, preclude the successful invasion of these species.
These results have implications for the transient response of communities and ecosystems to global change.
Response of forest plant species to land‐use change: a life‐history trait‐based approach
Authors: Verheyen Kris , Honnay Olivier , Motzkin Glenn , Hermy Martin , Foster David R. 
Published: July 2003

Summary

Classifying species by shared functional characteristics is important if common functional response groups are to be identified among different taxa.
We investigated plant traits that determine the response of forest plant species to land use changes using literature data. Sources from eight European countries and four North‐eastern American states, comprising 20 field studies yielded information on 216 forest plant species. For these species, data on 13 life history traits were collected.
Trait correlation structure was similar in the European and American data‐sets and corresponded well to those described in the literature. The European and American herbs and the European graminoids were clustered into distinct emergent groups based on their plant traits. The profiles of the European and American emergent groups were similar.
Herb species belonging to emergent groups characterized by low dispersability (i.e. large seeds, low fecundity, unassisted dispersal) were relatively slow colonizers. Dispersability (and not recruitment) seems to be a key factor limiting the colonization of some forest plant species. The relationship between dispersability and colonizing capacity was less clear for graminoids.
A life history trait‐based approach offers good opportunities to gain insight into the mechanisms behind species response to land‐use change.
The dynamics of nitrogen movement in an Arctic salt marsh in response to goose herbivory: a parameterized model with alternate stable states
Authors: Walker N. A. , Henry H. A. L. , Wilson D. J. , Jefferies R. L. 
Published: July 2003

Summary

LPBN is a parameterized simulation model of flows of nitrogen (N) in an ecosystem of cyanobacteria, grass and grazers, based on the N dynamics of a grazed Puccinellia lawn in an intertidal marsh on Hudson Bay. This system shows two alternate stable states: (a) lawns that either support a foraging population of lesser snow geese, or are not grazed by geese; and (b) exposed saline sediments that support little or no vegetation. The model represents the flow of N from cyanobacterial fixation, the major N input into the system, to the geese that migrate in autumn; those that do not return represent the major N output from the system. We have modelled N fixation, the transformations of N in the soil, plant growth, lawn regeneration, and goose grazing and grubbing.
The model simulates steady‐state flows of N similar to those observed in the field at zero and at moderate goose density, and it also simulates the transition to the state of zero plant biomass, a consequence of increased grubbing at high goose density. The simulated steady‐state flows are found to be more sensitive to changes in the parameters that describe N fixation and goose biology, than to similar changes in the parameters describing plant biology.
Because the model shows the alternate stable states and the transition between them, with values for the state variables that are consistent with field data, we conclude that N dynamics are crucial in determining the stability of the real salt marsh‐goose system. The determining factor is the loss of the input of N from fixation when lawn area is reduced because the rate of goose grubbing exceeds that of plant re‐establishment.
Plant amino acid uptake, soluble N turnover and microbial N capture in soils of a grazed Arctic salt marsh
Authors: Henry Hugh A. L. , Jefferies Robert L. 
Published: July 2003

Summary

The uptake of free amino acids by the grass Puccinellia phryganodes was investigated in soils of an Arctic coastal salt marsh, where low temperatures and high salinity limit inorganic nitrogen (N) availability, and the availability of soluble organic N relative to inorganic N is often high.
Following the injection of 13C15N‐amino acid, 15N‐ammonium and 15N‐nitrate tracers into soils, rates of soluble nitrogen turnover and the incorporation of 13C and 15N into plant roots and shoots were assessed. Chloroform fumigation‐extraction was used to estimate the partitioning of labelled substrates into microbial biomass.
Free amino acids turned over rapidly in the soil, with half‐lives ranging from 8.2 to 22.8 h for glycine and 8.9 to 25.2 h for leucine, compared with 5.6 to 14.7 h and 5.6 to 15.6 h for ammonium and nitrate, respectively. 15N from both organic and inorganic substrates was incorporated rapidly into plant tissue and the ratio of 13C/15N incorporation into plant tissue indicated that at least 5–11% of 13C15N‐glycine was absorbed intact.
Microbial C and N per unit soil volume were 1.7 and 5.4 times higher, respectively, than corresponding values for plant C and N. Plant incorporation of 15N tracer was 56%, 83% and 68% of the comparable incorporation by soil microorganisms of glycine, ammonium and nitrate ions, respectively.
These results indicate that P. phryganodes can absorb amino acids intact from the soil despite competition from soil microorganisms, and that free amino acids may contribute substantially to N uptake in this important forage grass utilized by lesser snow geese in the coastal marsh.
Lack of relationship between below‐ground competition and allocation to roots in 10 grassland species
Authors: Cahill James F. 
Published: July 2003

Summary

A field experiment in a native grassland in Central Alberta, Canada, tested whether plants alter relative allocation to roots vs. shoots in response to below‐ground competition, and whether the mass of a species’ root system accounts for interspecific differences in below‐ground competitive response.
Seedlings of each of 10 native species were transplanted into the naturally occurring vegetation in the field at the start of the growing season. Root interactions between the target plants and their neighbours were manipulated through the use of PVC root exclusion tubes, with target plants grown with or without potential root interactions with their neighbours. Neighbour shoots were also tied back, forcing any target–neighbour interactions to be below ground.
Below‐ground competition generally reduced plant growth, with its relative magnitude varying among species.
An allometric analysis indicated that competition below ground did not result in an increase in the relative biomass allocated to roots for any of the 10 target species. This is counter to the growth‐balance hypothesis (and optimal foraging theory). Below‐ground competition did increase root : shoot ratios, but this was due to reduced plant size (small plants have larger root : shoot ratios), rather than adaptive plasticity.
A species’ below‐ground competitive ability was not related to its root system size. Although this finding is counter to commonly made assumptions, it is supported by other work demonstrating below‐ground competition to be generally size‐symmetric.
Despite the majority of plant–plant interactions in grasslands being below ground, our understanding of plant competition above ground is significantly more robust. Several wide‐spread assumptions regarding below‐ground competition are suspect, and more multispecies studies such as this are required to provide a fuller picture of how plants respond to, and compete for, soil resources.
Habitat fragmentation affects the common wetland specialist Primula farinosa in north‐east Switzerland
Authors: Lienert Judit , Fischer Markus 
Published: July 2003

Summary

Fragmentation reduces size and increases isolation of plant habitats, and increases the ratio between edge and centre area. Consequences of habitat fragmentation have rarely been studied for common plants, and edge effects are rarely studied for plants in general. We studied density, population structure, fitness components and biotic interactions in the locally abundant distylous fen plant Primula farinosa in the centres and at the edges of 27 Swiss fen habitats of different size and degree of isolation.
Population sizes ranged from 80 to 106 450 flowering plants and were larger in larger fen habitats than in smaller ones.
The densities of plants were lower in more isolated habitats (by 26–46% depending on developmental stage). In the less isolated habitats, the density of seedlings and juveniles was higher in larger habitats. Plant densities were lower at the edge than in the centre of habitats (34–55%), and edges had fewer plants of younger developmental states. Densities of reproductive plants differed only in the centres of habitats, where they were higher in larger habitats, while at the edges these densities were independent of habitat area.
Flower morph proportions were independent of size and isolation of habitats.
Plants in larger habitats had larger rosette diameters and tended to have more flowers.
At edges, seed set was on average 11% lower, and occurrence and degree of herbivory more than 50% higher, than in centres. Capsule frugivory was less likely in larger habitats. Infection by the smut fungus Urocystis primulicola was more likely in larger habitats.
We conclude that size, isolation and edge to centre ratio of fen habitats all affect the abundant P. farinosa and recommend that edge effects and more common species are given more attention.
Facilitated invasion by hybridization of Sarcocornia species in a salt‐marsh succession
Authors: Figueroa M. E. , Castillo J. M. , Redondo S. , Luque T. , Castellanos E. M. , Nieva F. J. , Luque C. J. , Rubio‐Casal A. E. , Davy A. J. 
Published: July 2003

Summary

We examined salt marsh development over 17 years (1984–2001) in a rapidly accreting, well‐drained lagoon of a macrotidal marsh in south‐west Spain. Scattered, elevated tussocks of colonizing Spartina maritima expanded radially until they either coalesced or were separated only by narrow drainage channels. We recorded changes in elevation of the tussocks and investigated the cover and biomass of successive species invading them.
Sediment accretion produced a mean annual increase in tussock elevation of 3.5 cm. Sarcocornia perennis had begun to invade the raised centres of the tussocks by 1984, subsequently displacing Spartina maritima radially to become dominant by 1990. A hybrid form of Sarcocornia, which appeared on some of the tussocks occupied by S. perennis in 1997, also expanded radially and had achieved dominance on many of the invaded tussocks by 2001, by virtue of its more erect growth form and rapid accumulation of high above‐ and below‐ground biomass.
Tussocks not yet invaded by the hybrid remain dominated by S. perennis and have maintained sediment accretion rates and redox potentials similar to those that have been invaded.
Genetic analysis, using random amplified DNA (RAPD) markers, indicated that the hybrid was a cross between the diploid Sarcocornia perennis (2n = 18) and the octaploid S. fruticosa (2n = 72), a high‐marsh species, and suggested that each hybrid individual may have resulted from a separate pollination of an indigenous S. perennis plant.
Invasion by the new hybrid thus probably occurred as a result of pollen flow from high‐marsh S. fruticosa, some 1 km distant, to the stigmas of the established dominant S. perennis. Succession might therefore be facilitated genetically rather than simply by the enhanced sediment accretion, which ameliorated the effects of submersion and low sediment redox potentials that presumably exclude S. fruticosa from lower parts of the marsh.
Self/non‐self discrimination in roots
Authors: Falik Omer , Reides Perla , Gersani Mordechai , Novoplansky Ariel 
Published: July 2003

Summary

Competition usually involves the allocation of limiting resources to non‐reproductive functions. Natural selection is expected to favour mechanisms that increase competition with non‐self neighbours and limit wasteful competition with self.
We used Pisum sativum plants that had two roots and ‘double plants’ with two shoots and two roots that could be either longitudinally separated into two genetically identical but physiologically distinct individuals or left intact.
Root development was significantly greater in split‐root plants whose neighbours belonged to different plants. Furthermore, root development was relatively greater in the presence of roots of a different plant, regardless of its identity. This discrimination had a vectorial component whereby plants developed more and longer lateral roots towards neighbouring roots of different plants than towards other roots of the same plant.
The results thus demonstrate a mechanism of avoiding self‐competition that is based on physiological co‐ordination among different organs of the same plant rather than on allochemical recognition that depends on genetic differences.
The ability to discriminate between self and non‐self could be expected to increase resource use efficiency and ecological performance in plants. It could also be expected that tight physiological co‐ordination will be selected for between organs of the same plant that have greater probability of being engaged in direct competitive interactions with each other.