Fe3O4 nanoparticles affect paddy soil microbial-driven carbon and nitrogen processes: roles of surface coating and soil types

Abstract

Magnetic Fe₃O₄ nanoparticles (nFe₃O₄) are the most widely used nanomaterials and are inevitably introduced to soils. To overcome particle agglomeration, nFe₃O₄ are often coated with protective agents. However, scarce information has addressed the impacts of surface coating of nFe₃O₄ on biochemical processes and microbial properties in soil. In this study, a laboratory incubation experiment was employed to reveal the response of gas production, mineral N content, enzymatic activities and soil bacterial community to nFe₃O₄ and meso-2,3-dimercaptosuccinic acid coated nFe₃O₄ (nFe₃O₄@DMSA) in three representative paddy soils in China, i.e. lateritic soil (LS), Wushan soil (WS), and red soil (RS). The results showed that nFe₃O₄@DMSA, rather than nFe₃O₄, influenced these parameters profoundly, with varying effects in the soil types. Specifically, in RS nFe₃O₄@DMSA, rather than nFe₃O₄, promoted the CH₄ production, soil NH₄-N concentration, and soil enzymatic activities of β-xylanase (BX) and β-N-acetylglucosaminidase (NAG), but decreased the CO₂ production and β-glucosidase (BG) activity. By contrast, in LS and WS nFe₃O₄@DMSA led to increases in CO₂ emission, soil NH₄-N content, and BG, BX, and NAG activities, but a decrease in CH₄ production. Data from 16S rRNA gene sequencing showed the varying responses to the nanoparticles in terms of soil bacterial taxa and putative functional groups. The methanogens and the N-fixation group had strong affinities with the CH₄ production and NH₄-N content, respectively. Geobacter was closely related to the CH₄ production in all soils. Anaeromyxobacter, Azospirillum, and Burkholderia–Caballeronia–Paraburkholderia had close relationships with the N-fixation group/NH₄-N content in LS, WS and RS, respectively. Collectively, nFe₃O₄@DMSA changed the microbial-driven biochemical process in the soils, depending on the soil types. Caution should be paid to the complex interaction between the soil matrix and nanoparticle types for better management of nanoparticles in future.