Reactivity and composition of phytoplankton-derived organic matter: implications for the marine Carbon cycle
[eng] Marine phytoplankton are responsible for approximately half of the photosynthetic production of organic matter (OM) and oxygen in Earth. The composition and reactivity of phytoplankton- derived OM influences two of the main C-sequestration mechanisms of the ocean: the biological carbon pump an...
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| Tipo de recurso: | tesis doctoral |
| Estado: | Versión publicada |
| Fecha de publicación: | 2023 |
| País: | España |
| Institución: | Universidad de Barcelona |
| Repositorio: | Dipòsit Digital de la UB |
| OAI Identifier: | oai:diposit.ub.edu:2445/195982 |
| Acceso en línea: | https://hdl.handle.net/2445/195982 http://hdl.handle.net/10803/687986 |
| Access Level: | acceso abierto |
| Palabra clave: | Fitoplàncton marí Geoquímica orgànica Espectròmetres Cicle del carboni (Biogeoquímica) Marine phytoplankton Organic geochemistry Spectrometers Carbon cycle (Biogeochemistry) |
| Sumario: | [eng] Marine phytoplankton are responsible for approximately half of the photosynthetic production of organic matter (OM) and oxygen in Earth. The composition and reactivity of phytoplankton- derived OM influences two of the main C-sequestration mechanisms of the ocean: the biological carbon pump and the microbial carbon pump. Phytoplankton-derived OM can be classified as particulate (POM) or dissolved (DOM) and these size-fractions are subject to diverse production, consumption and transport processes involving biotic and abiotic interactions. Understanding how these processes influence OM composition and reactivity is essential to accurately describe the role of phytoplankton ecology in the marine Carbon cycle and ultimately in the regulation of Earth climate. This thesis aims, precisely, to better understand the controls over these processes. To do so, we combined fluorescence spectroscopy and elemental analysis of POM and DOM with multiple biotic and abiotic parameters during the development and decay of phytoplankton proliferations in micro- and mesocosm experiments and under natural conditions. The microcosm degradation experiment revealed that POM derived from diatom-dominated proliferations is degraded at a much slower rate than that of POM produced by a mixed phytoplankton community. In addition, accumulation of DOM of apparent recalcitrant nature was observed during the processing of diatom-derived POM. The analysis of four phytoplankton proliferations in Antarctic waters revealed that protein-like fluorescent OM was contributed by dissolved and particulate materials. The abundance and composition of phytoplankton and their interactions with viruses and grazers were identified as the main controls over the quantity and fractionation of protein-like fluorescent OM. By contrast, humic-like substances were mostly in the dissolved fraction, and their composition was related to photochemical degradation and microbial transformation. The mesocosm experiment showed that the balance between production and degradation of protein-like fluorescent DOM was controlled by the nitrogen availability of the planktonic community. Whereas the humic-like fluorescent DOM composition was influenced by photochemical processes and production of specific humic-like substances by autotrophic and heterotrophic prokaryotes, the taxonomic composition of eukaryotic phytoplankton did not have a profound influence over the fluorescent DOM composition. Overall, this thesis shows that the composition of plankton assemblages, and the interactions between organisms and between organisms and environmental conditions influence the composition and reactivity of phytoplankton-derived OM, ultimately determining its fate and role in the marine Carbon cycle. |
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