Compensatory Effects Between CO<sub>2</sub>, Nitrogen Deposition, and Nitrogen Fertilization in Terrestrial Biosphere Models Without Nitrogen Compromise Projections of the Future Terrestrial Carbon Sink
Sian Kou‐Giesbrecht, Vivek K. Arora
Abstract
Abstract Although terrestrial biosphere models (TBMs) with and without nitrogen cycling successfully reproduce the historical terrestrial carbon sink, the influence of nitrogen cycling under interacting and intensifying global change drivers in the future is unclear. Here, we compare TBM projections with and without nitrogen cycling over alternative future scenarios (the Shared Socioeconomic Pathways) to examine how representing nitrogen cycling influences CO 2 fertilization as well as the effects of a comprehensive group of physical and socioeconomic global change drivers. Because elevated nitrogen deposition and nitrogen fertilization have stimulated terrestrial carbon sequestration over the historical period, a model without nitrogen cycling must exaggerate the strength of CO 2 fertilization to compensate for these unrepresented nitrogen processes and to reproduce the historical terrestrial carbon sink. As a result, it cannot realistically project the future terrestrial carbon sink, overestimating CO 2 fertilization as the trajectories of CO 2 , nitrogen deposition and nitrogen fertilization diverge in future scenarios.