Acid rain reduces soil CO2 emission and promotes soil organic carbon accumulation in association with decreasing the biomass and biological activity of ecosystems: A meta-analysis

Acid rain, as one of the global environmental issues, alters the biogeochemistry of terrestrial ecosystems. However, the responses of soil greenhouse gases (GHGs) emissions to acid rain remain unclear, thus creating large uncertainties in the prediction of global climate change. Here, we conducted a meta-analysis based on existing 42 studies to assess the influences of acid rain on soil GHGs emissions. Results showed that acid rain significantly decreased soil CO2 emission by 11.7%, but marginally increased soil N2O emission by 11.7%. In addition, acid rain significantly decreased soil pH, dissolved organic carbon (C), microbial biomass C, nitrate nitrogen (N), hydrolysable N and total phosphorus, while increased soil organic C, ammonium N and C/N ratio. Moreover, acid rain significantly decreased the activity of soil urease, sucrase and invertase. Acid rain significantly decreased soil bacterial and gram-negative bacterial biomass, while increased the microbial biomass of gram-positive bacteria, fungi and actinomycete, and the ratios of fungi/bacteria and gram-positive/gram-negative bacteria. Furthermore, acid rain significantly decreased the aboveground biomass and fine root biomass of vegetation. The effect size of soil CO2 emission had significantly positive relationships with that of soil pH, microbial biomass C, urease activity, and fine root biomass, while it negatively related with that of soil organic C and C/N ratio. These findings suggest that acid rain reduces soil CO2 emission and promotes soil organic C accumulation.