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The lipid composition of swimming spores, cysts and five hour germlings was established. Spores utilized triglycerides first, then phospholipids. Upon encystment all glycolipid components decreased, while in germlings the phospholipids, monoglycerides and sterol esters exhibited a marked increase. 相似文献
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Various laboratory techniques have been utilized worldwide for measuring lead-210 in sub-recent deposits through its grand-daughter product polonium-210. Isotope dilution alpha spectrometry proved a suitable tool for absolute determination of lead-210 for the dating of aquatic deposits. Moreover, isotope dilution alpha spectrometry along with speciation experiments can be used to resolve depositional anomalies arising from supported lead-210/Ra-226 disequilibrium levels and unsupported lead-210 mobile fractions. Isotope dilution alpha spectrometry of sub-recent sediment and peat deposits has been critically evaluated for more than ten years. Our results show that type, size and composition of deposits analyzed as well as radiochemical procedures used, together with alpha counting techniques, are important factors influencing lead-210 determinations and tailing corrections using its granddaughter product polonium-210. Optimization of these parameters is of prime importance to achieve economic and accurate analyses, especially at low lead-210 concentrations and small sample sizes. 相似文献
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《Plant Ecology & Diversity》2013,6(2-3):227-241
Background: Although forest floor forms a large biomass pool in forested peatlands, little is known about its role in ecosystem carbon (C) dynamics. Aim: We aimed to quantify forest floor photosynthesis (P FF) and respiration (R FF) as a part of overall C dynamics in a drained peatland forest in southern Finland. Methods: We measured net forest floor CO2 exchange with closed chambers and reconstructed seasonal CO2 exchange in the prevailing plant communities. Results: The vegetation was a mosaic of plant communities that differed in CO2 exchange dynamics. The reconstructed growing season P FF was highest in the Sphagnum community and lowest in the feather moss communities. On the contrary, R FF was highest in the feather moss communities and lowest in the Sphagnum community. CO2 assimilated by the forest floor was 20–30% of the total CO2 assimilated by the forest. The forest floor was a net CO2 source to the atmosphere, because respiration from ground vegetation, tree roots and decomposition of soil organic matter exceeded the photosynthesis of ground vegetation. Conclusions: Tree stand dominates C fluxes in drained peatland forests. However, forest floor vegetation can have a noticeable role in the C cycle of peatlands drained for forestry. Similarly to natural mires, Sphagnum moss-dominated communities were the most efficient assimilators of C. 相似文献
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Estimating the extent of biological invasions is critical in predicting the effect of exotic species. We investigated the occurrence and number of alien freshwater plants and give information on the composition of alien aquatic flora, their trend in time, invasion pathway, and their invasive character. 相似文献