Atmospheric carbon dioxide: a driver of photosynthetic eukaryote evolution for over a billion years?

Exciting evidence from diverse fields, including physiology, evolutionary biology, palaeontology, geosciences and molecular genetics, is providing an increasingly secure basis for robustly formulating and evaluating hypotheses concerning the role of atmospheric carbon dioxide (CO 2 ) in the evolution of photosynthetic eukaryotes. Such studies span over a billion years of evolutionary change, from the origins of eukaryotic algae through to the evolution of our present-day terrestrial floras, and have relevance for plant and ecosystem responses to future global CO 2 increases. The papers in this issue reflect the breadth and depth of approaches being adopted to address this issue. They reveal new discoveries pointing to deep evidence for the role of CO 2 in shaping evolutionary changes in plants and ecosystems, and establish an exciting cross-disciplinary research agenda for uncovering new insights into feedbacks between biology and the Earth system.