Estimates of soil nutrient limitation on the CO 2 fertilization effect for tropical vegetation.

The CO 2 fertilization effect in tropical forests is a key factor for the global land carbon sink. We show that the normalized CO 2 effect on tropical vegetation carbon was c. 70% lower in seedling CO 2 experiments without nutrient fertilizers and c. 50% and 70% lower in models that consider nitrogen and phosphorus cycles, based on two model ensembles. The inadequate representation or lack of nutrient cycles in Earth System models likely leads to overestimating future tropical carbon gains.