Abstract:[Objective] This study was conducted to explore the effect and mechanism of Shewanella putrefaciens CN32, a typical bacterium secretes extracellular polymeric substances (EPS), on the release of clay-sorbed NH4+ in soils. [Methods] The common clay minerals in soil, including smectite, vermiculite, smectite-illite mixlayer mineral and biotite were used for NH4+ sorption and then was inoculated by S. putrefaciens CN32. The contents of clay-sorbed N, dissolved NH4+, the microbial biomass and EPS were monitored to understand the variation of NH4+ release from different types of the clay minerals. [Results] The content of clay-sorbed NH4+ was dependent on clay types, with high to low in smectite > vermiculite > smectite-illite mixlayer mineral (in biotite was too low). With the activity of S. putrefaciens CN32, the percentage of released NH4+ was highest in smectite, followed by in smectite-illite mixlayer mineral and lowest in vermiculite. Although CN32 effectively promoted the release of clay-sorbed NH4+, the released NH4+ did not accumulate in the solution but assimilated by the bacterial cells, which was transformed into bio-organic nitrogen (mainly EPS) and attached on the clay surface. The adsorption of EPS was highest on smectite, followed by smectite-illite mixlayer mineral and vermiculite. FTIR analysis revealed that the adsorption of both NH4+ and EPS on clays were closely associated with the hydroxyl groups in minerals (structural or interlayer water), thus, it is speculated that the competitive adsorption on mineral hydroxyl may be one of the important reasons for stimulated release of NH4+ by CN32. [Conclusion] The results of the present study demonstrated that the EPS-producing S. putrefaciens CN32 can promote the release of clay-sorbed NH4+ from all kinds of clay minerals. The released NH4+ does not necessary to be leached from the soil profile but instead to be transformed into organic nitrogen and increases the bioavailability of nitrogen fertilizer. Therefore, microorganisms may play an important role in reducing nitrogen loss and easing ammonia pollution from soils. It is important to systematically understand the microbial effects on the migration and transformation of clay-sorbed NH4+ in different types of soils (with different assemble of clay minerals), which serves for the precise prediction of the efficiency and loss risk of nitrogen fertilizers in soils.