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71.
Persisting chronic gastritis and elevated Helicobacter pylori antibodies after successful eradication therapy 总被引:1,自引:0,他引:1
AIM: The persistence of chronic inflammation in gastric mucosa and elevated Helicobacter pylori antibodies after successful eradication therapy are common findings in clinical practice. We studied their possible association with each other and disappearance in long-term follow up, as well as their possible connection with gastric atrophy. PATIENTS AND METHODS: The study population consisted of 108 dyspeptic patients with successful eradication therapy median 6.4 years earlier. The patients underwent gastroscopy, and biopsies from antrum and corpus were evaluated by an experienced pathologist. Serum samples collected from 77 patients were studied for H. pylori antibodies, parietal cell antibodies, as well as for pepsinogen I, pepsinogen II, and gastrin-17 levels. RESULTS: The prevalence of chronic gastric inflammation and elevated H. pylori antibodies after successful eradication therapy decreased by time, but still after 5 years, 17 of 51 (33%) subjects had elevated H. pylori antibodies and 14 of 68 (21%) had a mild inactive chronic inflammation in gastric mucosa. In patients with and without chronic inflammation in gastric mucosa, elevated H. pylori antibodies were detected in three of 10 (30%) and 14 of 41 (34%), elevated parietal cell antibodies in one of 10 (10%) and six of 41 (15%), low pepsinogen I in one of 10 (10%) and none of 41, and elevated gastrin-17 in three of 10 (30%) and six of 41 (15%), respectively. CONCLUSION: More than 5 years after successful H. pylori eradication therapy, mild persistent chronic inflammation may occur in gastric mucosa in up to one-fifth and elevated H. pylori antibodies even in one-third of patients, although these two are independent phenomena. 相似文献
72.
Tuomi Maria Stark Sari Hoset Katrine S. Väisänen Maria Oksanen Lauri Murguzur Francisco J. A. Tuomisto Hanna Dahlgren Jonas Bråthen Kari Anne 《Ecosystems》2019,22(4):827-843
Ecosystems - Mammalian herbivores shape the structure and function of many nutrient-limited or low-productive terrestrial ecosystems through modification of plant communities and plant–soil... 相似文献
73.
74.
Kaisa Heimonen Anu Valtonen Sari Kontunen‐Soppela Sarita Keski‐Saari Matti Rousi Elina Oksanen Heikki Roininen 《Oikos》2015,124(8):1013-1022
Climate warming has been predicted to increase the abundance of herbivorous insects. Together with concurrent poleward shifts in many insect species this may increase herbivore pressure on plants. However, the manner in which plants at higher latitudes become colonized by herbivorous insects in the future is unknown. We established a translocation experiment using 26 micropropagated silver birch Betula pendula genotypes from six populations originating from 60°N to 67°N, to study the susceptibility of the translocated birches to local herbivores. The birches were planted at three different latitudes in Finland (60°N, 62°N and 67°N). We studied the effect of source population and latitudinal translocation on herbivore density, species richness, and community composition among the genotypes growing in the same environmental conditions in two years; 2011 and 2012. The source population explained the variation in the herbivore density only in 2012, whereas latitudinal translocation did not affect herbivore density. Variation in species richness was not explained by the source population or by the latitudinal translocation. At two of the study sites, the similarity of the herbivore communities among the populations decreased with increasing latitudinal distance of the source populations, possibly because birch populations that grow geographically closer to each other are genetically more similar, and therefore support a more similar composition of the arthropod community. All birch genotypes were colonized by local herbivores, suggesting that as herbivores shift their ranges polewards, they are able to colonize novel host‐plant genotypes. This enables compositional changes in insect communities on their host plants in the future, which in turn, might affect total herbivory and eventually, plant growth. 相似文献
75.
Katrine S. Hoset Kukka Kyrö Tarja Oksanen Lauri Oksanen Johan Olofsson 《Ecography》2014,37(9):894-901
The relative importance of top‐down and bottom‐up mechanisms in shaping community structure is still a highly controversial topic in ecology. Predatory top‐down control of herbivores is thought to relax herbivore impact on the vegetation through trophic cascades. However, trophic cascades may be weak in terrestrial systems as the complexity of food webs makes responses harder to predict. Alternatively, top‐down control prevails, but the top‐level (predator or herbivore) changes according to productivity levels. Here we show how spatial variation in the occurrence of herbivores (lemmings and voles) and their predators (mustelids and foxes) relates with grazing damage in landscapes with different net primary productivity, generating two and three trophic level communities, during the 2007 rodent peak in northern Norway. Lemmings were most abundant on the unproductive high‐altitude tundra, where few predators were present and the impact of herbivores on vegetation was strong. Voles were most common on a productive, south facing slope, where numerous predators were present, and the impacts of herbivores on vegetation were weak. The impact of herbivores on the vegetation was strong only when predators were not present, and this cannot be explained by between‐habitat differences in the abundance of plant functional groups. We thus conclude that predators influence the plant community via a trophic cascade in a spatial pattern that support the exploitation ecosystems hypothesis. The responses to grazing also differed between plant functional groups, with implications for short and long‐term consequences for plant communities. 相似文献
76.
Johan Olofsson Lauri Oksanen Tarja Oksanen Maria Tuomi Katrine S. Hoset Risto Virtanen Kukka Kyrö 《Ecosystems》2014,17(4):606-615
Both the theory and the observations suggest that, there are strong links between herbivores and plants in terrestrial ecosystems; although, the effect of herbivores on plant community biomass is often attributed to variations in plant palatability. The existence of a strong link is commonly tested by constructing exclosures that exclude herbivores during a period of time. We here present data from two long-term (9 and 20 years, respectively) herbivore exclosure studies in lemming habitats on arctic tundra in northernmost Norway. The exclusion of all mammalian herbivores triggered strong increases in community level plant biomass and substantial changes in plant community composition. Palatable plants like graminoids and large bryophytes, as well as unpalatable plants like evergreen ericoids, deciduous shrubs, and lichens were all favored by excluding lemmings. These results reveal that a substantial increase in community biomass which occurs only when plant species capable of accumulating biomass are present, and palatability is a poor predictor of long-term responses of plants to excluding herbivores. 相似文献
77.
Hypersaline environments are dominated by archaea and bacteria and are almost entirely devoid of eukaryotic organisms. In addition, hypersaline environments contain considerable numbers of viruses. Currently, there is only a limited amount of information about these haloviruses. The ones described in detail mostly resemble head-tail bacteriophages, whereas observations based on direct microscopy of the hypersaline environmental samples highlight the abundance of non-tailed virus-like particles. Here we studied nine spatially distant hypersaline environments for the isolation of new halophilic archaea (61 isolates), halophilic bacteria (24 isolates) and their viruses (49 isolates) using a culture-dependent approach. The obtained virus isolates approximately double the number of currently described archaeal viruses. The new isolates could be divided into three tailed and two non-tailed virus morphotypes, suggesting that both types of viruses are widely distributed and characteristic for haloarchaeal viruses. We determined the sensitivity of the hosts against all isolated viruses. It appeared that the host ranges of numerous viruses extend to hosts in distant locations, supporting the idea that there is a global exchange of microbes and their viruses. It suggests that hypersaline environments worldwide function like a single habitat. 相似文献
78.
Structural characteristics and chemical composition of birch (Betula pendula) leaves are modified by increasing CO2 and ozone 总被引:1,自引:0,他引:1
Elina Oksanen Johanna Riikonen†‡ Seija Kaakinen‡ Toini Holopainen† Elina Vapaavuori‡ 《Global Change Biology》2005,11(5):732-748
Impacts of ozone and CO2 enrichment, alone and in combination, on leaf anatomical and ultrastructural characteristics, nutrient status and cell wall chemistry in two European silver birch (Betula pendula Roth) clones were studied. The young soil‐growing trees were exposed in open‐top chambers over three growing seasons to 2 × ambient CO2 and/or ozone concentrations in central Finland. The trees were measured for changes in altogether 35 variables of leaf structure, nutrients and cell wall chemistry of green leaves, and 20 of the measured variables were affected by CO2 and/or O3. Elevated CO2 increased the size of chloroplasts and starch grains, number of mitochondria, P : N ratio, and contents of cell wall hemicellulose. Elevated CO2 decreased the total leaf thickness, specific leaf area, concentrations of N, K, Cu, S and Fe, and contents of cell wall α‐cellulose, uronic acids, acid‐soluble lignin and acetone‐soluble extractives. Elevated ozone led to thinner leaves, higher palisade to spongy ratio, increased number of peroxisomes and mitochondria, reduced content of Mn, Zn, Cu, hemicellulose and uronic acids, and lower Mn : N and Zn : N ratios. In the combined exposure, interactions were antagonistic. Ultrastructural changes became more evident towards the end of the exposure. Young leaves were tolerant against ozone‐caused oxidative stress, whereas oxidative H2O2 accumulation was found in older leaves. CO2 enrichment improved ozone tolerance not only through increased photosynthesis rates, but also through changes in cell wall chemistry (hemicellulose, in particular). However, nutrient imbalances due to ozone and/or CO2 may predispose the trees to other biotic and abiotic stresses. Down‐regulation and up‐regulation of photosynthesis under elevated CO2 through anatomical changes is discussed. 相似文献
79.
V. Freiwald E. Häikiö R. Julkunen-Tiitto J. K. Holopainen & E. Oksanen 《Entomologia Experimentalis et Applicata》2008,128(1):66-72
In this study, we tested the impact of moderately elevated ozone (O3 ) – 1.5 × ambient, equivalent to predicted near-future ozone concentrations – on the feeding behaviour of the common leaf weevil Phyllobius pyri L. (Coleoptera: Curculionidae), on two hybrid aspen [ Populus tremula × Populus tremuloides (Salicaceae)] clones (clones 55 and 110) differing in ozone sensitivity using the open-air ozone exposure site in Kuopio, Finland. Three host-selection tests (test between treatments, test between clones, and test between treatments* clones) with common leaf weevil females were carried out in the laboratory in the 2nd year of ozone exposure. The beetles were offered two (four for the tests between treatments and clones) freshly cut leaf discs from first flush leaves. After 24 h, the beetles were removed and the leaf disc area consumed was measured. In the field, the unfolding of the buds was followed and samples were taken for anatomical and chemical (salicylates, condensed tannins, nitrogen, and water content) leaf analyses. Phyllobius pyri significantly preferred leaves from clone 55 to those from clone 110 in the ambient air treatment, whereas this preference was less evident under elevated ozone. Leaves from ozone-exposed trees were significantly preferred to leaves grown in ambient air. Our results suggest that the preference of clone 55 and of ozone-exposed leaves can be explained by phenotypic properties of the plant and prevailing ozone concentration through shifts in leaf development process, phenolic composition, and leaf thickness. 相似文献
80.
Janne Sundell Lenka Trebatická Tarja Oksanen Otso Ovaskainen Marko Haapakoski Hannu Ylönen 《Population Ecology》2008,50(3):257-266
In prey communities with shared predators, variation in prey vulnerability is a key factor in shaping community dynamics.
Conversely, the hunting efficiency of a predator depends on the prey community structure, preferences of the predator and
antipredatory behavioural traits of the prey. We studied experimentally, under seminatural field conditions, the preferences
of a predator and the antipredatory responses of prey in a system consisting of two Myodes species of voles, the grey-sided vole (M. rufocanus Sund.) and the bank vole (M. glareolus Schreb.), and their specialist predator, the least weasel (Mustela nivalis nivalis L.). To quantify the preference of the weasels, we developed a new modelling framework that can be used for unbalanced data.
The two vole species were hypothesised to have different habitat-dependent vulnerabilities. We created two habitats, open
and forest, to provide different escape possibilities for the voles. We found a weak general preference of the weasels for
the grey-sided voles over the bank voles, and a somewhat stronger preference specifically in open habitats. The weasels clearly
preferred male grey-sided voles over females, whereas in bank voles, there was no difference. The activity of voles changed
over time, so that voles increased their movements immediately after weasel introduction, but later adjusted their movements
to times of lowered predation risk. Females that were more active had an elevated mortality risk, whereas in the case of males,
the result was the opposite. We conclude that, in vulnerability to predation, the species- or habitat-specific characteristics
of these prey species are playing a minor role compared to sex-specific characteristics. 相似文献