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41.
Host trees for obligate epiphytes are dynamic patches that emerge, grow and fall, and metacommunity diversity critically depends
on efficient dispersal. Even though species that disperse by large asexual diaspores are strongly dispersal limited, asexual
dispersal is common. The stronger dispersal limitation of asexually reproducing species compared to species reproducing sexually
via small spores may be compensated by higher growth rates, lower sensitivity to habitat conditions, higher competitive ability
or younger reproductive age. We compared growth and reproduction of different groups of epiphytic bryophytes with contrasting
dispersal (asexual vs. sexual) and life history strategies (colonists, short- and long-lived shuttle species, perennial stayers)
in an old-growth forest stand in the boreo-nemoral region in eastern Sweden. No differences were seen in relative growth rates
between asexual and sexual species. Long-lived shuttles had lower growth rates than colonists and perennial stayers. Most
groups grew best at intermediate bark pH. Interactions with other epiphytes had a small, often positive effect on growth.
Neither differences in sensitivity of growth to habitat conditions nor differences in competitive abilities among species
groups were found. Habitat conditions, however, influenced the production of sporophytes, but not of asexual diaspores. Presence
of sporophytes negatively affected growth, whereas presence of asexual diaspores did not. Sexual species had to reach a certain
colony size before starting to reproduce, whereas no such threshold existed for asexual reproduction. The results indicate
that the epiphyte metacommunity is structured by two main trade-offs: dispersal distance vs. reproductive age, and dispersal
distance vs. sensitivity to habitat quality. There seems to be a trade-off between growth and sexual reproduction, but not
asexual. Trade-offs in species traits may be shaped by conflicting selection pressures imposed by habitat turnover and connectivity
rather than by species interactions.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
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We studied the relative importance of local habitat conditions and landscape structure for species richness of vascular plants, bryophytes and lichens in dry grasslands on the Baltic island of Öland (Sweden). In addition, we tested whether relationships between species richness and vegetation cover indicate that competition within and between the studied taxonomic groups is important. We recorded species numbers of vascular plants, bryophytes and lichens in 4 m2 plots (n=452), distributed over dry grassland patches differing in size and degree of isolation. Structural and environmental data were collected for each plot. We tested effects of local environmental conditions, landscape structure and vegetation cover on species richness using generalized linear mixed models. Different environmental variables explained species richness of vascular plants, bryophytes and lichens. Environmental effects, particularly soil pH, were more important than landscape structure. Interaction effects of soil pH with other environmental variables were significant in vascular plants. Plot heterogeneity enhanced species richness. Size and degree of isolation of dry grassland patches significantly affected bryophyte and lichen species richness, but not that of vascular plants. We observed negative relationships between bryophyte and lichen species richness and the cover of vascular plants. To conclude, effects of single environmental variables on species richness depend both on the taxonomic group and on the combination of environmental factors on a whole. Dispersal limitation in bryophytes and lichens confined to dry grasslands may be more common than is often assumed. Our study further suggests that competition between vascular plants and cryptogams is rather asymmetric. 相似文献
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Alexandra Philipsen Alexandra P. Lam Sigrid Breit Caroline Lücke Helge H. Müller Swantje Matthies 《Attention deficit and hyperactivity disorders》2017,9(2):101-111
The main purpose of this study was to examine whether adult patients with attention deficit hyperactivity disorder (ADHD) demonstrate sets of dysfunctional cognitive beliefs and behavioural tendencies according to Jeffrey Young’s schema-focused therapy model. Sets of dysfunctional beliefs (maladaptive schemas) were assessed with the Young Schema Questionnaire (YSQ-S2) in 78 adult ADHD patients and 80 control subjects. Patients with ADHD scored significantly higher than the control group on almost all maladaptive schemas. The ‘Failure’, ‘Defectiveness/Shame’, ‘Subjugation’ and ‘Emotional Deprivation’ schemas were most pronounced in adult ADHD patients, while only ‘Vulnerability to Harm or Illness’ did not differ between the two groups. The schemas which were most pronounced in adult patients with ADHD correspond well with their learning histories and core symptoms. By demonstrating the existence of early maladaptive schemas in adults suffering from ADHD, this study suggests that schema theory may usefully be applied to adult ADHD therapy. 相似文献
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Anaerobic bacteria are the oldest terrestrial creatures. They occur ubiquitously in soil and in the intestine of higher organisms and play a major role in human health, ecology, and industry. However, until lately no antibiotic or any other secondary metabolite has been known from anaerobes. Mining the genome sequences of Clostridium spp. has revealed a high prevalence of putative biosynthesis genes (PKS and NRPS), and only recently the first antibiotic from the anaerobic world, closthioamide, has been isolated from the cellulose degrading bacterium Clostridium cellulolyticum. The successful genetic induction of antibiotic biosynthesis in an anaerobe encourages further investigations of obligate anaerobes to tap their hidden biosynthetic potential. 相似文献
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The anaerobic rumen bacterium Wolinella succinogenes was able to grow by respiration with dimethylsulphoxide (DMSO) as electron acceptor and formate or H2 as electron donors. The growth yield amounted to 6.7 g and 6.4 g dry cells/mol DMSO with formate or H2 as the donors, respectively. This suggested an ATP yield of about 0.7 mol ATP/mol DMSO. Cell homogenates and the membrane fraction contained DMSO reductase activity with a high K
m (43 mM) for DMSO. The electron transport from H2 to DMSO in the membranes was inhibited by 2-(heptyl)-4-hydroxyquinoline N-oxide, indicating the participation of menaquinone. Formation of DMSO reductase activity occurred only during growth on DMSO, presence of other electron acceptors (fumarate, nitrate, nitrite, N2O, and sulphur) repressed the DMSO reductase activity. DMSO can therefore be used by W. succinogenes as an acceptor for phosphorylative electron transport, but other electron acceptors are used preferentially.Abbreviations
DMN
2,3-Dimethyl-1,4-naphthoquinone
-
DMNH
2
Reduced DMN
-
DMS
Dimethylsulphide (CH3)2S
-
DMSO
Dimethylsulphoxide (CH3)2SO
-
HQNO
2-(Heptyl)-4-hydroxyquinoline-N-oxide
-
TMAO
Trimethylamine-N-oxide
-
Y
s
Growth yield for substrate S 相似文献
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Rapid antigenic-type replacement and DNA sequence evolution of canine parvovirus. 总被引:34,自引:14,他引:20
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C R Parrish C F Aquadro M L Strassheim J F Evermann J Y Sgro H O Mohammed 《Journal of virology》1991,65(12):6544-6552
Analysis of canine parvovirus (CPV) isolates with a panel of monoclonal antibodies showed that after 1986, most viruses isolated from dogs in many parts of the United States differed antigenically from the viruses isolated prior to that date. The new antigenic type (designated CPV type 2b) has largely replaced the previous antigenic type (CPV type 2a) among virus isolates from the United States. This represents the second occurrence of a new antigenic type of this DNA virus since its emergence in 1978, as the original CPV type (CPV type 2) had previously been replaced between 1979 and 1981 by the CPV type 2a strain. DNA sequence comparisons showed that CPV types 2b and 2a differed by as few as two nonsynonymous (amino acid-changing) nucleotide substitutions in the VP-1 and VP-2 capsid protein genes. One mutation, resulting in an Asn-Asp difference at residue 426 in the VP-2 sequence, was shown by comparison with a neutralization-escape mutant selected with a non-CPV type 2b-reactive monoclonal antibody to determine the antigenic change. The mutation selected by that monoclonal antibody, a His-Tyr difference in VP-2 amino acid 222, was immediately adjacent to residue 426 in the three-dimensional structure of the CPV capsid. The CPV type 2b isolates are phylogenetically closely related to the CPV type 2a isolates and are probably derived from a common ancestor. Phylogenetic analysis showed a progressive evolution away from the original CPV type. This pattern of viral evolution appears most similar to that seen in some influenza A viruses. 相似文献
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