AbstractsBiology & Animal Science

Microbial plankton form the basis of the food web in aquatic habitats. Due to their vast abundances they influence the cycling of elements and the Earth’s climate at a global scale. This thesis aims at a better understanding of how environmental factors such as temperature and the availability of nutrients and light affect the growth and functioning of microbial plankton communities. The thesis combines experimental studies and mathematical modelling to address open questions in community ecology that range from rather detailed questions on the physiology and growth of marine N2-fixing cyanobacteria to more general questions on the mechanism controlling the species composition and functioning of entire communities. The insights obtained from this thesis show that temperature, nutrients and light have interactive effects on the growth and functioning of microbial plankton communities. Under ideal growth conditions temperature strongly increases plankton growth rates, suggesting that global warming will have a strong direct effect on the growth and species composition of plankton communities in eutrophic systems. However, low nutrient concentrations and low light availability dampen the effect of temperature, suggesting that oligotrophic ecosystems are generally more constrained by nutrient limitation than by temperature. Furthermore, the temperature response varies among species depending on their physiological traits. In particular, our results suggest that global warming will favor marine N2-fixing cyanobacteria more than other phytoplankton species. The results obtained in this thesis are therefore highly relevant in the context of global climate change and anthropogenic changes in nutrient cycling.