Acid deposition promotes soil carbon sequestration in terrestrial ecosystems of China

Background and aimsChina has experienced a high rate of anthropogenic acid deposition for more than four decades, which can greatly affect ecosystem carbon (C)-cycling processes. However, a comprehensive assessment of how acid deposition alters C input and output and its potential impacts on soil C sequestration across a wide range of terrestrial ecosystems remains lacking.MethodsWe synthesized 1660 observations from 77 simulated acid deposition experiments in China to quantify the acid-addition effects on ten C-cycling variables.ResultsWe found that acid addition significantly decreased both above-and below-ground biomass (-7.2% and -8.3%, respectively), dissolved organic C (-7.6%), microbial biomass C (-10.2%), and soil respiration (-9.4%) (-7.0% for autotrophic respiration and -5.8% for heterotrophic respiration), but significantly increased soil organic C (2.5%). The significant negative effects of acid addition on both plant biomass and auto-/ hetero-trophic respiration were found in subtropical forests, and the significant positive effect of acid addition on soil organic C was found in all ecosystems except for the temperate forests. The response of plant biomass to acid addition was strongly affected by acid addition strength, and the responses of heterotrophic respiration and soil organic C were significantly correlated with experimental duration or initial soil pH.ConclusionOur results provide direct evidence that anthropogenic acid deposition promotes soil C sequestration mainly through decreasing C output (i.e., heterotrophic respiration), and should be incorporated into C-cycling models for estimating soil C sequestration potential under future environmental changes.