Element interactions limit soil carbon storage

Rising levels of atmospheric CO₂ are thought to increase C sinks in terrestrial ecosystems. The potential of these sinks to mitigate CO₂ emissions, however, may be constrained by nutrients. By using metaanalysis, we found that elevated CO₂ only causes accumulation of soil C when N is added at rates well above typical atmospheric N inputs. Similarly, elevated CO₂ only enhances N₂ fixation, the major natural process providing soil N input, when other nutrients (e.g., phosphorus, molybdenum, and potassium) are added. Hence, soil C sequestration under elevated CO₂ is constrained both directly by N availability and indirectly by nutrients needed to support N₂ fixation.