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排序方式: 共有132条查询结果,搜索用时 31 毫秒
91.
Gesa A. Weyhenmeyer Pirkko Kortelainen Sebastian Sobek Roger Müller Miitta Rantakari 《Ecosystems》2012,15(8):1295-1307
The quantity of carbon dioxide (CO2) emissions from inland waters into the atmosphere varies, depending on spatial and temporal variations in the partial pressure of CO2 (pCO2) in waters. Using 22,664 water samples from 851 boreal lakes and 64 boreal streams, taken from different water depths and during different months we found large spatial and temporal variations in pCO2, ranging from below atmospheric equilibrium to values greater than 20,000???atm with a median value of 1048???atm for lakes (n?=?11,538 samples) and 1176???atm for streams (n?=?11,126). During the spring water mixing period in April/May, distributions of pCO2 were not significantly different between stream and lake ecosystems (P?>?0.05), suggesting that pCO2 in spring is determined by processes that are common to lakes and streams. During other seasons of the year, however, pCO2 differed significantly between lake and stream ecosystems (P?<?0.0001). The variable that best explained the differences in seasonal pCO2 variations between lakes and streams was the temperature difference between bottom and surface waters. Even small temperature differences resulted in a decline of pCO2 in lake surface waters. Minimum pCO2 values in lake surface waters were reached in July. Towards autumn pCO2 strongly increased again in lake surface waters reaching values close to the ones found in stream surface waters. Although pCO2 strongly increased in the upper water column towards autumn, pCO2 in lake bottom waters still exceeded the pCO2 in surface waters of lakes and streams. We conclude that throughout the year CO2 is concentrated in bottom waters of boreal lakes, although these lakes are typically shallow with short water retention times. Highly varying amounts of this CO2 reaches surface waters and evades to the atmosphere. Our findings have important implications for up-scaling CO2 fluxes from single lake and stream measurements to regional and global annual fluxes. 相似文献
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94.
T. Eggermann Hartmut Engels Christiane Heidrich-Kaul Inge Moderau Gesa Schwanitz 《Human genetics》1997,99(4):521-522
We report a patient with a de novo translocation 13/18, identified by high-resolution banding. The breakpoints were ascertained
by fluorescence in situ hybridisation with whole chromosome 13 and 18 paints. Short tandem repeat typing demonstrated the
aberration to be of combined maternal/paternal origin and thereby confirmed its de novo and postzygotic formation. Thus, a
gonadal mosaic in one of the parents resulting in a higher recurrence risk could be excluded.
Received: 1 September 1996 / Revised: 3 November 1996 相似文献
95.
96.
Following massive persecution and eradication, strict legal protection facilitated a successful reestablishment of wolf packs in Germany, which has been ongoing since 2000. Here, we describe this recolonization process by mitochondrial DNA control-region sequencing, microsatellite genotyping and sex identification based on 1341 mostly non-invasively collected samples. We reconstructed the genealogy of German wolf packs between 2005 and 2015 to provide information on trends in genetic diversity, dispersal patterns and pack dynamics during the early expansion process. Our results indicate signs of a founder effect at the start of the recolonization. Genetic diversity in German wolves is moderate compared to other European wolf populations. Although dispersal among packs is male-biased in the sense that females are more philopatric, dispersal distances are similar between males and females once only dispersers are accounted for. Breeding with close relatives is regular and none of the six male wolves originating from the Italian/Alpine population reproduced. However, moderate genetic diversity and inbreeding levels of the recolonizing population are preserved by high sociality, dispersal among packs and several immigration events. Our results demonstrate an ongoing, rapid and natural wolf population expansion in an intensively used cultural landscape in Central Europe.Subject terms: Conservation biology, Population genetics 相似文献
97.
Wójcik M Ramadori P Blaschke M Sultan S Khan S Malik IA Naz N Martius G Ramadori G Schultze FC 《Histochemistry and cell biology》2012,137(2):217-233
It has been suggested that cyclooxygenase-2 (COX-2)-mediated prostaglandin synthesis is associated with liver inflammation
and carcinogenesis. The aim of this study is to identify the cellular source of COX-2 expression in different stages, from
acute liver injury through liver fibrosis to cholangiocarcinoma (CC). We induced in rats acute and “chronic” liver injury
(thioacetamide (TAA) or carbon tetrachloride (CCl4)) and CC development (TAA) and assessed COX-2 gene expression in normal and damaged liver tissue by RT-PCR of total RNA.
The cellular localization of COX-2 protein in liver tissue was analyzed by immunohistochemistry as well as in isolated rat
liver cells by Western blotting. The findings were compared with those obtained in human cirrhotic liver tissue. The specificity
of the antibodies was tested by 2-DE Western blot and mass spectrometric identification of the positive protein spots. RT-PCR
analysis of total RNA revealed an increase of hepatic COX-2 gene expression in acutely as well as “chronically” damaged liver.
COX-2-protein was detected in those ED1+/ED2+ cells located in the non-damaged tissue (resident tissue macrophages). In addition COX-2 positivity in inflammatory mononuclear
phagocytes (ED1+/ED2−), which were also present within the tumoral tissue was detected. COX-2 protein was clearly detectable in isolated Kupffer
cells as well as (at lower level) in isolated “inflammatory” macrophages. Similar results were obtained in human cirrhotic
liver. COX-2 protein is constitutively detectable in liver tissue macrophages. Inflammatory mononuclear phagocytes contribute
to the increase of COX-2 gene expression in acute and chronic liver damage induced by different toxins and in the CC microenvironment. 相似文献
98.
99.
Karin Ekl?f Andrea Kraus Gesa A. Weyhenmeyer Markus Meili Kevin Bishop 《Ecosystems》2012,15(8):1308-1320
Forestry has been reported to cause elevated mercury (Hg) concentrations in runoff water. However, the degree to which forestry operations influence Hg in runoff varies among sites. A synoptic study, covering 54 catchments distributed all over Sweden, subjected to either stump harvest (SH), site preparation (SP) or no treatment (Ref), was undertaken to reveal the degree of forestry impact and causes of eventual variation. All streams were sampled twice, in autumn 2009 and summer 2010. There were no significant differences in total mercury (THg) and methylmercury (MeHg) concentrations between the three treatments in either 2009 or 2010. However, when pooling the treated catchments (that is, SH and SP) and taking catchment properties such as latitude into account, the treatment had a significant influence on the THg and MeHg concentrations. Although the treatment effect on THg and MeHg did not differ between SH and SP, the study did reveal significant forestry effects on potassium (K) and total nitrogen (TN) that were greater in the SH catchments and lower in the SP catchments. Partial least square (PLS) regressions indicated that organic matter was the most important variable influencing both the THg and MeHg concentrations. There were no significant differences between the treatment groups when comparing the ratios of THg/total organic carbon (TOC) and MeHg/TOC, suggesting that the high concentrations of THg and MeHg observed at some of the treated catchments are associated with increased concentrations of TOC rather than new methylation or increased mobilization caused by factors other than TOC. 相似文献
100.
Renee M. van Dorst Anna Grdmark Richard Svanbck Ulrika Beier Gesa A. Weyhenmeyer Magnus Huss 《Global Change Biology》2019,25(4):1395-1408
Climate change studies have long focused on effects of increasing temperatures, often without considering other simultaneously occurring environmental changes, such as browning of waters. Resolving how the combination of warming and browning of aquatic ecosystems affects fish biomass production is essential for future ecosystem functioning, fisheries, and food security. In this study, we analyzed individual‐ and population‐level fish data from 52 temperate and boreal lakes in Northern Europe, covering large gradients in water temperature and color (absorbance, 420 nm). We show that fish (Eurasian perch, Perca fluviatilis) biomass production decreased with both high water temperatures and brown water color, being lowest in warm and brown lakes. However, while both high temperature and brown water decreased fish biomass production, the mechanisms behind the decrease differed: temperature affected the fish biomass production mainly through a decrease in population standing stock biomass, and through shifts in size‐ and age‐distributions toward a higher proportion of young and small individuals in warm lakes; brown water color, on the other hand, mainly influenced fish biomass production through negative effects on individual body growth and length‐at‐age. In addition to these findings, we observed that the effects of temperature and brown water color on individual‐level processes varied over ontogeny. Body growth only responded positively to higher temperatures among young perch, and brown water color had a stronger negative effect on body growth of old than on young individuals. Thus, to better understand and predict future fish biomass production, it is necessary to integrate both individual‐ and population‐level responses and to acknowledge within‐species variation. Our results suggest that global climate change, leading to browner and warmer waters, may negatively affect fish biomass production, and this effect may be stronger than caused by increased temperature or water color alone. 相似文献