Nitrogen and phosphorus constrain the CO 2 fertilization of global plant biomass

Elevated CO 2 (eCO 2 ) experiments provide critical information to quantify the effects of rising CO 2 on vegetation 1 – 6 . Many eCO 2 experiments suggest that nutrient limitations modulate the local magnitude of the eCO 2 effect on plant biomass 1 , 3 , 5 , but the global extent of these limitations has not been empirically quantified, complicating projections of the capacity of plants to take up CO 2 7 , 8 . Here, we present a data-driven global quantification of the eCO 2 effect on biomass based on 138 eCO 2 experiments. The strength of CO 2 fertilization 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 CO 2 levels expected by 2100 can potentially enhance plant biomass by 12 ± 3% above current values, equivalent to 59 ± 13 PgC. The future effect of eCO 2 we derive from experiments is geographically consistent with past changes in greenness 9 , but is considerably lower than the past effect derived from models 10 . If borne out, our results suggest that the stimulatory effect of CO 2 on carbon storage could slow considerably this century. Our research provides an empirical estimate of the biomass sensitivity to eCO 2 that may help to constrain climate projections.