Nitrogen and phosphorus constrain the CO2 fertilization of global plant biomass

Abstract

Elevated CO₂ (eCO₂) experiments provide critical information to quantify the effects of rising CO₂ on vegetation^1–6. Many eCO₂ experiments suggest that nutrient limitations modulate the local magnitude of the eCO₂ 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 CO₂^7,8. 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 CO₂ levels expected by 2100 can potentially enhance plant biomass by 12 ± 3% above current values, equivalent to 59 ± 13 PgC. The future effect of eCO₂ we 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 CO₂ on carbon storage could slow considerably this century. Our research provides an empirical estimate of the biomass sensitivity to eCO₂ that may help to constrain climate projections.

Elevated CO₂ increases plant biomass, providing a negative feedback on global warming. Nutrient availability was found to drive the magnitude of this effect for the majority of vegetation globally, and analyses indicated that CO₂ will continue to fertilize plant growth in the next century.