Acid rain reduces plant-photosynthesized carbon sequestration and soil microbial network complexity

Acid rain threatens the structure and function of terrestrial ecosystems; however, the mechanisms by which acid rain affects the photosynthesized carbon (C) fluxes and soil microbial communities are far less understood, thus impeding accurate projections of regional C flux in the plant-soil-atmosphere system. In this study, we performed an isotopic 13C labeling experiment to trace C footprints in a maize-soil system under acid rain pollution (pH 4.5 and 3.0; SO42−/NO3−= 2:1). Our results showed that acid rain exerted a negligible effect on total plant biomass as well as shoot biomass. Acid rain of pH 3.0 inhibited plant 13C assimilation and the flow of fixed 13C to the soil. Acid rain decreased soil total C and organic nitrogen (N) but increased inorganic N (i.e., nitrate-N) content. The acid rain of pH 3.0 enhanced soil bulk density, led to soil acidification, and promoted soil microbial diversity. However, acid rain reduced the connectivity and complexity of soil microbial network. Soil 13C content was mainly regulated by soil pH, ammonium-N, and root biomass. Our findings demonstrated that acid rain reduces photosynthesized C sequestration of maize-soil system and soil microbial taxa interactions.