Disproportionate Soil Inorganic Carbon Loss and Associated CO2 Emission Driven by Soil Acidification

Summary

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.