Investigation of ferrous iron-involved anaerobic denitrification in three subtropical soils of southern China

Anaerobic microcosm experiments were conducted to study soil denitrification capacity and the role of endogenous ferrous iron as alternative electron donor in denitrification in De'an and Qujialing soils of southern China. Potential denitrification capacity, gaseous-N composition, as well as the relationships between ferrous iron and soil denitrification, and main edaphic environmental factors were investigated. After 24 days of anaerobic incubation, the potential denitrification rate for paddy soils in De'an (DP) was three to four times higher than red soils in De'an (DR) and paddy soils in Qujialing (QP) under 260 mg N kg(-1) inputs (N1). N-2 production was inhibited under N1 in paddy soils but not in red soils. Substantial decline of Fe2+ and NO3 (-)-N contents along with Fe3+ increase appeared in DP soil under N1, suggesting that Fe2+-oxidizing NO3 (-)-N reduction occurred. However, no obvious Fe2+-involved autotrophic denitrification processes were observed in DR and QP soils, which appeared to be restricted by less available ferrous iron. Pearson's correlation analysis showed that soil pH and Fe3+ content were the dominant edaphic factors affecting Fe2+-involved denitrification processes. Soil denitrification capacity of paddy soils is greater than red soils and the reduction activities of N2O are more susceptible to intensive N loads in paddy soils compared to the red soils in De'an and Qujialing regions. Significant ferrous iron-involved autotrophic denitrification processes may exist in paddy soils of De'an but not in the other two soils.