Phytoplankton facing global change: Ecological and physiological perspectives

Abstract

The global change induced by human action is the result of the interaction of multiple abiotic factors. Today, a crucial field of research concerns the study of how ecosystems will respond to future environmental conditions, since global-change factors interact synergistically or antagonistically and can aggravate or mitigate the effects of this phenomenon. In this thesis, an analysis is undertaken concerning the alteration of three abiotic factors associated with the current climatic crisis (temperature increase; greater UV radiation-exposure and increase in nutrient concentration) and the impact on phytoplanktonic organisms, located at the base of aquatic trophic webs, from a physiological and ecological perspective. The connection between these two aspects has scarcely been studied, despite that an understanding of physiological responses is necessary to understand ecological dynamics. Furthermore, this thesis focuses on photosynthetic microorganisms that have phagotrophic ability within the same cell (i.e. mixotrophic protists). In recent decades, this metabolic capacity has been discovered to be widespread among phytoplankton groups. Therefore, it becomes critical to determine how mixotrophic cells might respond to global-change factors, regulating their metabolism towards autotrophy or heterotrophy, as well as to examine the implications for the energy and nutrient fluxes. This thesis is designed to help fill these information gaps carrying out experiments and observational studies over different time scales (from hours to years); at different levels of biological organization (from the cell to ecosystems); and with organisms from different environments (natural marine samples, freshwater and laboratory cultures).