Nitrate alleviate dissimilatory iron reduction and arsenic mobilization by driving microbial community structure change

Abstract

Anaerobic situation induced by long-term flooding of paddy soils makes dissimilatory iron (Fe) reduction and Arsenic (As) reduction in pore water. In our research, different dosage of nitrate (1 and 20 mmol NO3− kg−1 soil, LN and HN, respectively) were used as amendments for As immobilization. The effect on soil properties such as pH, Eh, sulfate, and nitrate; the effect on As(III) and dissimilatory iron reduction and the effect on microbial community structure were investigated. Our results showed that With the addition of nitrate, the reduction of Eh was accelerated. Especially for HN, the Eh decreased from 139 to 40 mV in 30 days, is higher than Eh in original soil (CK). The dissimilatory iron reduction was significantly depressed by the addition of nitrate, Fe2+ in nitrate amendments are much less than control, especially for HN, Fe2+ concentration was 62.58% lower than control. While Final As(III) concentrations were 284.67, 223.87, and 190.70mg Kg−1 for CK, LN, and HN treatments, respectively. In both LN and HN, the concentration of NO3− faded with incubation time, which means that NO3− could act as an electron acceptor instead of Fe3+ and As(V). Moreover, nitrate has selectivity for microbes, while the abundance of Clostridia and Geobacteraceae, which play a major role in the reduction of dissimilatory iron, is strongly inhibited, thereby inhibiting the process of dissimilatory iron reduction. Our results showed that by promotion of decreasing Eh, inhibition dissimilatory iron reduction, and Arsenic speciation transformation, nitrate could act as an effective amendment for As immobilization in paddy soils.