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Lisa Bjørnlund Søren Mørk Mette Vestergård Regin Rønn 《Biology and Fertility of Soils》2006,43(1):1-11
The aim was to study the effects of P fertilization and leaf aphid attack on the trophic interactions of bacteria and bacterial feeders in the rhizospheres of barley plants. The density of protozoa peaked in the rhizospheres of plants fertilized with N and P, whereas nematodes peaked in the rhizospheres of plants to which only N had been added. Fingerprinting of bacterial communities by length heterogeneity polymerase chain reaction revealed differences in community structure between NP rhizospheres and N rhizospheres as well as aphid-related differences within N rhizospheres. Specifically, α-proteobacteria increased with P addition. To evaluate if differences in bacteria in terms of their quality as food could partly explain the observed differences in protozoan and nematode abundances, growth of the flagellate Cercomonas sp. was assessed with 935 bacteria isolated from the different treatments. This assay indicated that bacterial isolates were of higher food quality to Cercomonas sp. in NP than in N rhizospheres when plants were subjected to aphid attack. Bacteria of high and low food quality for Cercomonas sp., respectively, were fed to the nematode Caenorhabditis elegans and larval production examined. α-Proteobacteria supported the growth of Cercomonas sp. well, whereas Actinobacteria did not. In contrast, C. elegans reproduced poorly on most α-proteobacteria but were able to reproduce well on some Actinobacteria. These results suggest that the different response of protozoa and nematodes to P addition could be mediated through a food quality-related change in community composition of bacteria and that leaf aphid attack may interfere with nutrient effects on bacterial assemblages of rhizospheres. 相似文献
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Regin Arge Magny S Thomassen Rolf K Berge Jose L Zambonino‐Infante Bendik Fyhn Terjesen Maike Oehme Kjell‐Arne Rørvik 《Aquaculture Research》2014,45(5):922-933
Effects of dietary tetradecylthioacetic fatty acid (TTA) on muscle fat, development of gonads and early sexual maturation in S0 Atlantic salmon during the first year in sea were investigated. TTA (0.5% w/w) was added to the feeds for 8 weeks in the spring. In May, at the end of the TTA‐feeding period, the fish in the TTA group had significantly (P < 0.05) less fat (10.1%) stored in muscle compared with the control group (10.8%). In September, mean male gonadosomatic index (GSI) in maturing fish in the TTA group was found to be lower compared with the maturing fish in the control group (P = 0.05). On the basis of GSI values, male sexual maturation in September was 10.0% vs. 14.4% for the TTA and the control group respectively. Thus, relative to the control group, the incidence of male sexual maturation in the TTA group was reduced by about 1/3 (P = 0.002). Production data was not affected by dietary supplementation of TTA. This study reveals that TTA significantly reduces the incidence of male sexual maturation in S0 Atlantic salmon. A significant elimination model of TTA in fish muscle that takes into account, the growth rate of the fish was further developed in this study. 相似文献
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Improving production efficiency of farmed Atlantic salmon (Salmo salar L.) by isoenergetic diets with increased dietary protein‐to‐lipid ratio 
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下载免费PDF全文 Rúni Weihe Jens‐Erik Dessen Regin Arge Magny Sissel Thomassen Bjarne Hatlen Kjell‐Arne Rørvik 《Aquaculture Research》2018,49(4):1441-1453
The effects of isoenergetic diets with high (HP) and low (LP) protein‐to‐lipid ratios on feeding rate (SFR), feed conversion (FCR), growth (TGC) and relative‐ and absolute nutrient retention were investigated using both whole‐body weight (BW) and carcass weight (CW) to assess the production efficiency. Three different feeding trials in seawater were conducted: two large‐scale trials with yearling smolt (S1) and under‐yearling smolt (S0) and one small‐scale with S1 smolt. The initial body weights in the trials were 105, 319 and 978 g, respectively, and the fish were fed and monitored until they reached harvest weights. In all three trials, the dietary HP group attained significantly higher (p < .05) CW at harvest based on fish with equal BW. Also, fish fed the HP diets significantly improved FCR (p < .05) when based on CW. In the small‐scale trial, fish fed HP diet, especially during late autumn and spring, significantly (p < .001) improved FCRBW and FCRCW. Improved FCR coincided with significantly higher (p < .05) relative energy retention in the dietary HP group. In all three trials, the HP groups had significantly higher (p < .05) TGC with regard to both BW and CW. Taken together, the present studies indicate that growth performance and feed utilization in modern salmon farming has the potential to be further improved by increasing the dietary protein‐to‐lipid ratio. In addition, dietary influence is more precisely assessed when using carcass as the weight denominator when analysing feed utilization and growth performance. 相似文献
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Nematodes and flagellates are important bacterial predators in soil and sediments. Generally, these organisms are considered to be competitors for bacterial food. We studied the interaction among flagellates and nematodes using axenic liquid cultures amended with heat-killed bacteria as food and showed for the first time that a small and common soil flagellate (Cercomonas sp.) is able to attack and kill the much larger nematode Caenorhabditis elegans. The killing process is not caused by soluble metabolites but requires direct contact between the flagellate cells and the nematode surface and occurs rapidly (within a few hours) at high flagellate density. At lower flagellate density, adult nematodes sometimes avoid attachment of flagellates, feed on them and become the dominant bacterial predator. Considering that bacterial feeders affect bacterial communities differently, and that one bacterial feeder can control the abundance of another, suggests a new perspective on how bacterial diversity and trophic interactions are linked in the soil food web. 相似文献
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Sandel B Arge L Dalsgaard B Davies RG Gaston KJ Sutherland WJ Svenning JC 《Science (New York, N.Y.)》2011,334(6056):660-664
The effects of climate change on biodiversity should depend in part on climate displacement rate (climate-change velocity) and its interaction with species' capacity to migrate. We estimated Late Quaternary glacial-interglacial climate-change velocity by integrating macroclimatic shifts since the Last Glacial Maximum with topoclimatic gradients. Globally, areas with high velocities were associated with marked absences of small-ranged amphibians, mammals, and birds. The association between endemism and velocity was weakest in the highly vagile birds and strongest in the weakly dispersing amphibians, linking dispersal ability to extinction risk due to climate change. High velocity was also associated with low endemism at regional scales, especially in wet and aseasonal regions. Overall, we show that low-velocity areas are essential refuges for Earth's many small-ranged species. 相似文献
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The increase in protozoan and nematode populations following addition of glucose or barley leaf material to five different mixtures of a sandy loam and a silty clay loam was investigated in 2 experiments. Prescribed soil textures (varying in clay content from 15.6% to 28.6%) were incubated at a matric potential of —10 kPa at 15 °C, and the number of protozoa and nematodes and the amount of inorganic nitrogen were estimated after 0, 2 and 5 weeks. In the first experiment, the effect of amendment with glucose was compared with amendment with barley leaves. Numbers of protozoa increased in soil mixtures amended with both glucose and barley leaves, but nematodes only increased in the treatment with barley leaves. There was a large positive effect of the amount of fine-textured soil on the number of protozoa, whereas the nematodes were not affected by soil texture. In the second experiment, the effect of nematodes on protozoa and nitrogen mineralization was examined. Soil mixtures prepared with sterilised soil were amended with barley leaves and either (1) a soil suspension filtered through a 5 μm mesh to remove nematodes, or (2) a filtered soil suspension and a mixture of nematodes extracted from soil. The nematodes that multiplied in the soil mixtures were almost exclusively bacterial-feeding rhabditids. The nematodes had a significantly positive effect on the number of protozoa but an insignificant effect on N-mineralization. Both protozoa and nematodes were affected positively by the proportion of the fine-textured soil in the soil mixtures, but the positive effect on protozoa was larger than the effect on nematodes. 相似文献
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Three pesticides, dimethoate, pirimicarb and fenpropimorph, had a negative impact on the colonization of a sterilized soil by a natural population of soil protozoa. Fenpropimorph has an effect at the lowest concentration applied; 25 mg litre?1. Dimethoate reduced the soil respiration significantly for about 10 days after application. In single species cultures of soil protozoa in liquid media, a flagellate Cercomonas sp., was a better test organism than a ciliate, Colpoda sp., or an amoeba, Acanthamoeba sp., with respect to interpretation of dose-response curves and ease of observation. 相似文献
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