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Assembly processes of bacterioplankton communities in shallow lakes along anthropogenic gradients

Boek - Dissertatie

Bacteria play a fundamental role in the most important biogeochemical cycles in terrestrial and aquatic ecosystems. Despite the importance of bacterial communities for ecosystem processes and biodiversity, microbial ecology was for a long time limited to cultivation for the identification of species. However, over the last decades, a revolution occurred due to Next Generation Sequencing (NGS) methods that allow the identification of an elevated number of species and the possibility to correlate functional roles to the different species. As other communities, bacteria living in freshwater systems are facing different pressures related to anthropogenic actions (e.g., pollution, land use change and climate change). Thus, understanding how these bacterial communities are dealing with these different stressors and anthropogenic changes is urgent. Here, using the metacommunity framework, we evaluated the effects of different environmental pressures on bacterioplankton assembly. We estimated the relative importance of local and regional processes on taxonomic and functional profiles along gradients of environmental change. We carried out an extensive field sampling campaign along gradients of urbanization and eutrophication covering in total 145 shallow lakes and ponds. Besides, we performed a mesocosm experiment with 80 mesocosms to evaluate under experimental conditions how bacterioplankton assembly is affected by different levels of nutrient-enrichment, temperature increase and a zooplankton richness gradient. In chapter II, related to an urbanization gradient, we reported changes in bacterioplankton community composition in urban areas related to local environmental conditions, mainly driven by pH. This suggests species sorting as the prevalent assembly process in an urbanization context. In chapter III, we showed that local environmental conditions mediated by phytoplankton and zooplankton were more important in driving bacterioplankton assembly along a eutrophication gradient compared to regional factors. This result indicates the importance to include biotic interactions as explanatory variables in studies of bacterioplankton assembly. In chapter IV, we combined taxonomic composition, functional group annotations and carbon utilization profiles to compare the local and regional drivers in bacterioplankton assembly. Local environment was the main driver for functional group annotations and taxonomic composition. Carbon utilization profiles could not be explained by environment or space. This pattern suggests that functional traits are complementary to understand bacterioplankton assembly, especially because functional traits were driven by different local variables. In chapter V, we used mesocosms under a setting of nutrient-enrichment, temperature increase and zooplankton richness to reproduce eutrophication scenarios and evaluate how bacterioplankton assembly is affected by these conditions. Biotic interactions mediated by different zooplankton species impacted significantly heterotrophic bacteria assembly. Divergent communities at the final time point were found to be correlated to the presence of Cyanobacteria. Nutrient and temperature treatments were less important in the trajectory of bacterioplankton communities after 12 weeks. Overall, our combination of different approaches - observational (taxonomic, functional and inclusion of biotic factors) and experimental (mesocosms) - contributed to a better understanding of bacterioplankton assembly in the context of environmental change (urbanization and eutrophication).
Jaar van publicatie:2022
Toegankelijkheid:Open