Nitrogen and phosphorus constrain the CO2fertilization of global plant biomass

Elevated CO2(eCO2) experiments provide critical information to quantify the effects of rising CO2on vegetation1–6. Many eCO2experiments suggest that nutrient limitations modulate the local magnitude of the eCO2effect on plant biomass1,3,5, but the global extent of these limitations has not been empirically quantified, complicating projections of the capacity of plants to take up CO27,8. Here, we present a data-driven global quantification of the eCO2effect on biomass based on 138 eCO2experiments. The strength of CO2fertilization is primarily driven by nitrogen (N) in ~65% of global vegetation and by phosphorus (P) in ~25% of global vegetation, with N- or P-limitation modulated by mycorrhizal association. Our approach suggests that CO2levels expected by 2100 can potentially enhance plant biomass by 12 ± 3% above current values, equivalent to 59 ± 13 PgC. The future effect of eCO2we derive from experiments is geographically consistent with past changes in greenness9, but is considerably lower than the past effect derived from models10. If borne out, our results suggest that the stimulatory effect of CO2on carbon storage could slow considerably this century. Our research provides an empirical estimate of the biomass sensitivity to eCO2that may help to constrain climate projections.