Atmospheric CO(2) enrichment generally stimulates plant photosynthesis and nutrient uptake, modifying the local and global cycling of bioactive elements. Although nutrient cations affect the long-term productivity and carbon balance of terrestrial ecosystems, little is known about the effect of CO(2) enrichment on cation availability in soil. In this study, we present evidence for a novel mechanism of CO(2)-enhancement of cation release from soil in rice agricultural systems. Elevated CO(2) increased organic C allocation belowground and net H(+) excretion from roots, and stimulated root and microbial respiration, reducing soil redox potential and increasing Fe(2+) and Mn(2+) in soil solutions. Increased H(+), Fe(2+), and Mn(2+) promoted Ca(2+) and Mg(2+) release from soil cation exchange sites. These results indicate that over the short term, elevated CO(2) may stimulate cation release from soil and enhance plant growth. Over the long-term, however, CO(2)-induced cation release may facilitate cation losses and soil acidification, negatively feeding back to the productivity of terrestrial ecosystems.