Nitrogen and phosphorus constrain the CO2 fertilization of global plant biomass

Elevated CO₂ (eCO₂) experiments provide critical information to quantify the effects of rising CO₂ on vegetation. Many eCO₂ experiments suggest that nutrient limitations modulate the local magnitude of the eCO₂ effect on plant biomass, but the global extent of these limitations has not been empirically quantified, complicating projections of the capacity of plants to take up CO₂. Here, we present a data-driven global quantification of the eCO₂ effect on biomass based on 138 eCO₂ experiments. The strength of CO₂ 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 CO₂levels expected by 2100 can potentially enhance plant biomass by 12 ± 3% above current values, equivalent to 59 ± 13 PgC. The global-scale response to eCO₂ we derive from experiments is similar to past changes in greenness and biomass with rising CO₂, suggesting that CO₂ will continue to stimulate plant biomass in the future despite the constraining effect of soil nutrients. Our research reconciles conflicting evidence on CO₂ fertilization across scales and provides an empirical estimate of the biomass sensitivity to eCO₂ that may help to constrain climate projections.