Terrestrial CO2 storage in plant biomass and soil: a negative relationship

Elevated CO₂ ( eCO₂ ) experiments provide critical information to quantify the capacity of terrestrial ecosystems to store carbon. eCO₂ experiments collectively suggest that nutrient limitations modulate the eCO₂ fertilization effect, but a global quantification of the effects of eCO₂on ecosystem-level carbon storage from eCO₂ experiments is still lacking. Here, we quantify the global magnitude of the eCO₂ effect on biomass and soil carbon based on data from eCO₂ experiments. Nitrogen (N) and phosphorus (P) availability support a 12±3% increase in global biomass above current values, equivalent to 59±13 petagrams of carbon, for an increase in atmospheric CO₂ of 250 ppm. However, the effect of eCO₂ on plant biomass has a direct and negative impact on soil carbon storage. Priming effects on soil carbon can diminish the positive effects of eCO₂ commonly observed in forest ecosystems, but increases in soil carbon in grasslands provide some ecosystem-level benefits on carbon storage that were previously not accounted for. Our research highlights the importance of accounting for changes in both plants and soils, and provides a mechanistic framework to quantify the land carbon sink using empirical observations.