Photosynthetic energy conversion efficiency in the ocean

The foundation of almost every ecosystem on Earth relies on photosynthetic organisms to convert sunlight energy into chemical bond energy. In aquatic ecosystems a diverse group of single celled organisms called phytoplankton are the prevalent gateway for biological energy, responsible for nearly half of Earth’s net primary production. Consequently, phytoplankton play a vital role not only in the dynamics of their respective environment, but also in global geochemical cycles. The first step in the photosynthetic process is the absorption of light energy, which can then drive a photochemical reaction, or alternatively dissipate via fluorescence or thermal dissipation. The efficiency of each pathway and the partitions between them collectively denote the physiological state of phytoplankton, which ultimately controls phytoplankton primary production. The research presented in this dissertation examines the mechanisms by which phytoplankton physiologically acclimate and adapt to rapid variations in nutrients and light. The methodological approach in this research relies on simultaneous measurements of chlorophyll a variable fluorescence and fluorescence lifetime in a laboratory study and in two oceanographic cruises. With this approach both the photochemical and fluorescence emission pathways efficiencies are directly measured, and the thermal dissipation efficiency is inferred. In chapter 1, I present a review of the topic. In chapter 2, I examine the role a family of LHCx proteins plays in photoprotection and regulation of the light harvesting complex functional size in diatoms. In chapter 3, focused on the West Antarctic Peninsula, I demonstrate the potential simultaneous measurements of the photochemical and fluorescence efficiencies have as a rapid diagnostic tool for in situ assessments of phytoplankton physiology in response to iron limitation. In chapter 4, I examine dynamics in phytoplankton physiology across the Equatorial Atlantic Ocean in response to infrequent upwelling events.Ph.D.Includes bibliographical reference