Ecology Letters (2010) 13: 284–291
Atmospheric CO2 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 CO2 enrichment on cation availability in soil. In this study, we present evidence for a novel mechanism of CO2-enhancement of cation release from soil in rice agricultural systems. Elevated CO2 increased organic C allocation belowground and net H+ excretion from roots, and stimulated root and microbial respiration, reducing soil redox potential and increasing Fe2+ and Mn2+ in soil solutions. Increased H+, Fe2+, and Mn2+ promoted Ca2+ and Mg2+ release from soil cation exchange sites. These results indicate that over the short term, elevated CO2 may stimulate cation release from soil and enhance plant growth. Over the long-term, however, CO2-induced cation release may facilitate cation losses and soil acidification, negatively feeding back to the productivity of terrestrial ecosystems.