Disproportionate Soil Inorganic Carbon Loss and Associated CO ₂ Emission Driven by Soil Acidification

Summary

Abstract Soil acidification induced by nitrogen fertilization and atmospheric deposition is widely assumed to deplete soil inorganic carbon (SIC), thereby generating substantial CO 2 emissions that amplify climate warming. However, national‐scale evidence linking acidification‐driven SIC loss to direct CO 2 release remains limited. Here we apply a 0.05° proton‐budget framework constrained by atmosphere–soil–vegetation data sets (1980–2020) and extend it to 2050 projections, to quantify acidification‐induced SIC depletion and associated CO 2 emissions across China's terrestrial ecosystems. As expected, soil acidification emerged as a dominant driver of SIC loss, accounting for ∼30%–56% of total depletion (2.57 ± 0.60 g C m −2  yr −1 or 13.04 ± 3.04 Tg C yr −1 ), with croplands contributing more than 70% of acidification‐driven losses. Contrary to prevailing assumptions, only 11 ± 3% of depleted SIC (1.52 ± 0.33 Tg C yr −1 ) was directly emitted as CO 2 , offsetting merely ∼8% of the carbon sink from natural carbonic acid–driven rock weathering. This contrast arises because SIC‐rich soils are typically circumneutral to alkaline, favoring dissolved bicarbonate export over CO 2 evasion. Meanwhile, continued policy regulation under the sustainable, low‐carbon, and environmentally friendly development pathway (SSP1‐2.6‐BHE) could further reduce SIC depletion and associated CO 2 emissions by 36% and 15%, respectively, by 2050. Overall, our findings demonstrate that acidification‐induced SIC depletion does not entirely translate into direct atmospheric CO 2 release, highlighting the need to explicitly distinguish SIC depletion from gaseous carbon loss in carbon‐cycle and climate assessments.