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The objective of this study was to investigate the effects of simultaneous application of ferrous iron [Fe(II)] and nitrate (NO 3 − ) on arsenic (As) accumulation in rice plants during the entire growth period. To this end, Fe(II) and NO 3 − were simultaneously applied to As-contaminated soil in a pot experiment conducted under climate-controlled greenhouse conditions. In comparison to the control and sole treatments with Fe(II), NO 3 − , or amorphous iron (Fe) oxides, the simultaneous application of Fe(II) and NO 3 − significantly reduced As bioavailability by enhancing As(V) immobilization in the soil and also significantly inhibited As accumulation in rice plants, especially that of iAs in the grain. The presence of Fe(II) and nitrate can decrease As releasing via inhibiting reductive dissolution of iron minerals, and the Fe(II) oxidation coupled with nitrate reduction can immobilize As via incorporating As into iron secondary minerals. Therefore, the simultaneous application of Fe(II) and NO 3 − effectively decreased As accumulation in rice plants by enhancing As oxidation/immobilization mediated by abiotic/biotic Fe redox transformation and mineralization. These findings provided new insights into the Fe/N/As biogeochemical cycles and are also important from the view of agronomic management of As toxicity and mitigation in As-contaminated paddy fields.

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In this paper, we consider a parabolic-elliptic system of partial differential equations in the three dimensional setting that arises in the study of biological transport networks. We establish the local existence of strong solutions and present a blow-up criterion. We also show that the solutions exist globally in time under the some smallness conditions of initial data and of the source.

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