CO₂ studies remain key to understanding a future world

Contents 34 I. 34 II. 36 III. 37 IV. 37 V. 38 38 References 38 SUMMARY: Characterizing plant responses to past, present and future changes in atmospheric carbon dioxide concentration ([CO₂ ]) is critical for understanding and predicting the consequences of global change over evolutionary and ecological timescales. Previous CO₂ studies have provided great insights into the effects of rising [CO₂ ] on leaf-level gas exchange, carbohydrate dynamics and plant growth. However, scaling CO₂ effects across biological levels, especially in field settings, has proved challenging. Moreover, many questions remain about the fundamental molecular mechanisms driving plant responses to [CO₂ ] and other global change factors. Here we discuss three examples of topics in which significant questions in CO₂ research remain unresolved: (1) mechanisms of CO₂ effects on plant developmental transitions; (2) implications of rising [CO₂ ] for integrated plant-water dynamics and drought tolerance; and (3) CO₂ effects on symbiotic interactions and eco-evolutionary feedbacks. Addressing these and other key questions in CO₂ research will require collaborations across scientific disciplines and new approaches that link molecular mechanisms to complex physiological and ecological interactions across spatiotemporal scales.