Quantification of the magnitude and possible manifestations of CO2 fertilization in terrestrial ecosystems, despite the overarching importance to understanding the fate of carbon cycling and also projected warming, remains highly uncertain. Tree-ring archives, as continuous records spanning the past centuries, appear to offer unique and powerful opportunities to address CO2 fertilization in natural environments, both via radial growth as a measure of carbon sequestration, and by using stable isotope ratios of wood tissue to obtain insights into the physiological processes connected to isotope discrimination such as diffusion and assimilation.
Results/Conclusions
Nevertheless, analyses of tree-ring data have not yet provided conclusive answers on the magnitude, spatiotemporal terrestrial carbon sink. In this talk I will review past investigations of CO2 fertilization, and use these investigations to outline both challenges and research opportunities. Recent advances have been made using isotopes on integrated and connected metrics such as the intrinsic water use efficiency. Yet growth responses remain highly uncertain. It is speculated that a combination of systematically sampled large-scale investigations, in conjunction with targeted work at remote sites with long-lived trees, will provide pathways forward. Successful studies will need to consider age/size trends, climate variability, ecosystem development, and potential sampling biases to more conclusively quantify and attribute CO2 fertilization effects in forest ecosystems.