Element interactions limit soil carbon storage

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Abstract
Rising levels of atmospheric CO 2 are thought to increase C sinks in terrestrial ecosystems. The potential of these sinks to mitigate CO 2 emissions, however, may be constrained by nutrients. By using metaanalysis, we found that elevated CO 2 only causes accumulation of soil C when N is added at rates well above typical atmospheric N inputs. Similarly, elevated CO 2 only enhances N 2 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 CO 2 is constrained both directly by N availability and indirectly by nutrients needed to support N 2 fixation.