As stressed by Schimel et al. 1995 , the uptake of atmospheric CO due to long-term increases in N deposition could increase as human N pollution increases; however, this increase may occur only up to a critical threshold loading value, beyond which any additional N input will cause significant ecosystem degradation (cf. Aber et al.,1989; Schultze,1989; Waring and Running 1998) More detailed studies are needed in order to accept or reject the tentative conclusions that we have drawn here, and we urge further additional research and modeling efforts to expand our under-standing of the links between unthropogenic N inputs and the global C cycle