Extracellular release of small and large molecules by phytoplankton in the Southern Bight of the North Sea     

Christiane Lancelot 《Estuarine, Coastal and Shelf Science》1984,18(1):65-77

Extracellular release by phytoplankton of small and large metabolites (molecular weight 〈and〉 500 d) is determined kinetically in various marine ecosystems including the eutrophic Scheldt estuary, the Belgian coastal zone and the oligotrophic English Channel. Kinetic curves show that while small metabolites are immediately released in the external medium, a lag phase is always observed in the release of large metabolites. Results indicate that 9–48% of the total excreted amount ends up in the small metabolites pool with no dependence on light intensity or nutritive conditions. Relative rates of heterotrophic uptake of the phytoplankton extracellular metabolites are calculated from the time dependent distribution of ¹⁴C labelled extracellular products. The data indicate that small molecules with high turnover rates (up to 25% h^?1) may occasionally be excreted by phytoplankton cells. The turnover time of high molecular weight excreted compounds is much longer. A correlation is found between the rate of production of these large extracellular metabolites and the exoenzymatic activity of the bacterial populations.  相似文献   

Metabolic changes in Phaeocystis poucheti (Hariot) Lagerheim during the spring bloom in Belgian coastal waters     

Christiane Lancelot 《Estuarine, Coastal and Shelf Science》1984,18(5):593-600

Incorporation of ¹⁴C-bicarbonate into the major intracellular end-products of photosynthesis (protein, polysaccharide, lipid) and two classes of exoproducts (oligomers and polymers) was measured in Belgian coastal waters at different stages of the spring phytoplankton bloom, entirely dominated by the alga Phaeocystis poucheti. It was shown that intracellular protein synthesis contributed 20–42% of the total intracellular ¹⁴C fixed and was positively correlated with the inorganic nitrogen content of the surrounding medium. The decrease of protein synthesis following nitrogen depletion is balanced by an increase of intracellular polysaccharide synthesis, which varies from 22 to 42% of the intracellular ¹⁴C fixed, and by an increase in extracellular release of high molecular weight material (18–60% of total ¹⁴C fixed) which forms a mucous envelope where cells are embedded. Lipid synthesis is not correlated with the ambient inorganic nitrogen content and represents a rather constant proportion (about 20%) of the intracellular ¹⁴C fixed.  相似文献   

Climate shifts vs. edaphic humidity and the difficulty of palaeoreconstructions – a malacological study on stable isotopes in Quaternary dune sequences of Fuerteventura     

Christiane Richter  Christopher-Bastian Roettig  Daniel Wolf  Andreas Gärtner  Thomas Kolb  Dominik Faust 《第四纪科学杂志》2021,36(3):426-440

Dune palaeosurface sequences on the Eastern Canary Islands were investigated for stable isotope records in gastropod shells of the genus Theba. Due to the ecology of the taxon and the special oceanic insularity of the study site, we assume that δ¹⁸O_shell signals in our case mainly reflect shifts in δ¹⁸O signals of sea surface water. We found that a rapid decrease in δ¹⁸O_shell signals is associated with significant changes in gastropod associations. We suggest that these faunal changes were caused by strong (hot) winds at the end of glacial phases, that were described previously by Moreno et al. In addition, we assume that rapid declines in δ¹⁸O_shell signals due to marine transgressions were followed by geomorphologically stable phases, dominated by dust enrichment. Such palaeosurfaces correlate with maxima of gastropod biodiversity and with more negative δ¹³C_shell signals indicating a higher proportion of C3 plants. Based on our results, we also assume that these silty palaeosurfaces were associated with increased soil moisture conditions due to a higher water storage capacity of the finer substrate, independent of climatic moisture conditions.  相似文献   

Characterization of a landslide-triggered debris flow at a rainforest-covered mountain region in Brazil     

Cabral  Victor Carvalho  Reis  Fábio Augusto Gomes Vieira  D’Affonseca  Fernando Mazo  Lucía  Ana  dos Santos Corrêa  Claudia Vanessa  Veloso  Vinicius  Gramani  Marcelo Fischer  Ogura  Agostinho Tadashi  Lazaretti  Andrea Fregolente  Vemado  Felipe  Pereira Filho  Augusto José  dos Santos  Claudia Cristina  Lopes  Eymar Silva Sampaio  Rabaco  Lis Maria Reoni  do Carmo Giordano  Lucilia  Zarfl  Christiane 《Natural Hazards》2021,108(3):3021-3043

Natural Hazards - Debris flows represent great hazard to humans due to their high destructive power. Understanding their hydrogeomorphic dynamics is fundamental in hazard assessment studies,...  相似文献