Terrestrial ecosystems have a massive capacity to capture carbon and mitigate anthropogenic global change. However, the build-up of plant and soil carbon pools depends heavily on the ability of plants and their below-ground symbionts to acquire soil resources to match demands set by their environment. Despite the importance of these below-ground dynamics, how plants adjust their resource-acquisition strategies under changing environmental conditions is not well understood. Will plants be able to adjust their strategies to access additional resources and increase carbon capture under future climate conditions? Our research focuses on how terrestrial ecosystems respond to various global change drivers such as rising CO2, nutrient pollution, human land use, and extreme weather events, and how these ecosystem responses, in turn, influence the trajectory of global change. Our work spans from tropical rainforests to the tundra and encompasses scales from physiology to ecosystems. The influence of symbiotic nitrogen-fixing plants on ecosystem dynamics, the below-ground responses of trees to elevated CO2, and the processes that drive soil carbon storage are particular foci of our work. We combine field and greenhouse experimental manipulations, large-scale observational studies, and global data analyses to illuminate the web of interactions between human activity, terrestrial ecosystem processes, and global change.