Acid rain mediated nitrogen and sulfur deposition alters soil nitrogen, phosphorus and carbon fractions in a subtropical paddy

Agricultural ecosystems are globally important sinks of carbon and other nutrient elements. In China, acid rain events affect about 0.62 million km2, representing about 6.4% of total land area; however, the impacts of acid rain mediated nitrogen (N) and sulfur (S) depositions on soil organic carbon (SOC) fractions and nutrient stocks in paddy soils and implications for yield production under climate change are unclear. We conducted a field experiment during two annual crop seasons to determine the effects of simulated acid rain on SOC fractions and nutrients in a subtropical paddy in China. Acid rain treatments comprised solutions of HNO3 + H2SO4 to simulate N and S deposition at pH levels of 4.5, 3.5, and 2.5. The results showed that content of soil C fractions varied with acid rain pH. Acid rain led to increased SOC concentrations and decreased the ratios of soil labile organic carbon (LOC): SOC and dissolved organic carbon (DOC): SOC concentrations, independently of crop season and growth stage. Soil salinity was positively associated with SOC suggesting that higher levels of salinity inhibit C decomposition favoring SOC accumulation. Treatment effects of acid rain on soil microbial C and N depended on crop growth stage. Concentration of Fe2+ was positively correlated with DOC in early and late paddy soils under acid rain, possibly as a result of Fe2+ retention by DOC, when Fe3+ is reduced to Fe2+. Acid rain led to increases in soil TN, TP, available N, NH4+ concentration, and SOC, and decreases in ratios of DOC: SOC, indicating decreases in soil biological activity and mineralization processes. Increases in dead rice plant biomass under acid rain were consistent with the increase in soil N and P concentrations, due to reduced nutrient uptake, and higher levels of total SOC.

Publication year:2020

Keywords:A1 Journal article

Accessibility:Open