Carbon and Nitrogen Cycle Dynamics in the O-CN Land Surface Model, II: The Role of the Nitrogen Cycle in the Historic Terrestrial C Balance

Abstract

Global-scale results of the new O-CN terrestrial biosphere model coupling the carbon (C) and 3nitrogen (N) cycles show that the model produces realistic estimates of present-day terrestrial C and N stocks and fluxes. N availability strongly affects high-latitude foliage area and foliage N, limiting vegetation productivity and present-day high-latitude net C uptake. Anthropogenic N deposition is predicted to have increased net primary productivity due to small increases in foliage area and foliage N, contributing 0.2-0.5 Pg C a-1 to the 1990s global net C uptake. While O-CN¿s modelled global 1990s terrestrial net C uptake (2.4 Pg C a-1) is similar to the estimate not accounting for anthropogenic N inputs and N dynamics (2.6 Pg C a-1), its latitudinal distribution and the sensitivity of the terrestrial C balance to its driving factors are substantially altered by the N cycle, with important implications for future trajectories of the global carbon cycle.