Shifting from a fertilization-dominated to a warming-dominated period.

Carbon dioxide and nitrogen fertilization effects on ecosystem carbon sequestration may slow down in the future because of emerging nutrient constraints, climate change reducing the effect of fertilization, and expanding land use change and land management and disturbances. Further, record high temperatures and droughts are leading to negative impacts on carbon sinks. We suggest that, together, these two phenomena might drive a shift from a period dominated by the positive effects of fertilization to a period characterized by the saturation of the positive effects of fertilization on carbon sinks and the rise of negative impacts of climate change. We discuss the evidence and processes that are likely to be leading to this shift.