Simultaneous minimization of arsenic mobilization and N2O emission in rice paddy soils
Final Report Abstract
Rice represents a major food source for millions of people worldwide. Traditional waterlogged rice cultivation induces reducing conditions under which natural, toxic arsenic can accumulate in rice grains. This cultivation method has implications for greenhouse gas production, as redox conditions are shifted towards methane formation. However, under nitrogen fertilization microbial denitrification causes the formation of nitrite as intermediate and N2 or N2O as final reaction products. Iron(II) can react abiotically with nitrite during the process of chemodenitrification, leading to N2O production. During both biotic iron(II) oxidation and chemodenitrification, iron(III) minerals form, which serve as highly reactive sorption templates for nutrients or contaminants, such as arsenic. The application of less or no fertilizer in waterlogged rice cultivation will shift redox conditions towards iron(III) reduction, remobilizing arsenic. Therefore, in this study, we aimed to find conditions under which we have lowest arsenic mobilization and greenhouse gas emissions (i.e., N2O and methane) to minimize healthand climate-related risks. In a microcosm study with paddy soil from Vercelli, Italy, that was carried out over 129 days, we applied nitrate fertilizer at different concentrations and different timepoints. We found that arsenic was rapidly scavenged by iron(III) minerals after fertilizer application, yet, also rapidly mobilized after nitrate depletion. Only the highest application rate could successfully retain arsenic on iron minerals over long-term. At the same time, N2O emissions were similarly high irrespective of fertilizer concentrations. This illustrates that timing and frequency of fertilizer application is crucial for controlling arsenic mobility and N2O emissions. In the same study, Gallionellaceae were more abundant under nitrate fertilization. By cultivation techniques, we were able to enrich a first lithoautotrophic nitrate-reducing, iron(II)-oxidizing culture from a paddy soil, which is dominated by Gallionellaceae. We quantified the extent of nitrate reduction, iron(II) oxidation, and identified N2O as the main product during denitrification. By combining experimental data with mathematical modelling, we were able to determine that not all of the N2O was biologically derived. 99.5 to 98.6% of N2O and 99.8 to 98.6% of iron(II) oxidation can be attributed to chemodenitrification under autotrophic and mixotrophic conditions, respectively. Further, we were able to show that labile, bioavailable organic carbon sources (acetate) tremendously impacted the microbial community composition shifting the enrichment culture towards more mixotrophic/heterotrophic denitrifiers (Dechloromonas sp., Acidovorax sp., Zoogloea sp., Parvibaculum sp.). Analyzing our data with different model structures that reflect and quantify our process understanding, we further showed that iron(II) oxidation and N2O production was almost completely biotically-derived. Overall, we were able to investigate dynamics in arsenic mobility and N2O emissions under various nitrate fertilization regimes and identified and enriched microbial key players responsible for nitrate-dependent iron(II) oxidation in paddy soils.
Publications
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Arsen in Grundwasser und Reis — Ursachen und Konsequenzen. BIOspektrum, 26(6), 676-678.
Joss, Hanna; Muehe, E. Marie & Kappler, Andreas
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Simultaneous minimization of arsenic mobilization and nitrous oxide emission under nitrogen fertilization in paddy soils. Goldschmidt2021 abstracts. European Association of Geochemistry.
Joss, Hanna; Joshi, Prachi; Maisch, Markus; Zhu, Yong-Guan; Muehe, E. Marie; Zarfl, Christiane & Kappler, Andreas
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Microorganisms control greenhouse gas emissions and arsenic mobility in nitrogen-fertilized paddy soils. Microbiology and Infection Biology Day, CMFI Exzellenzcluster
Grimm, H. & Kappler, A.
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Simultaneous minimization of arsenic mobilization and nitrous oxide emission under nitrogen fertilization in paddy soils. ACS Spring
Joss, H., Joshi, P., Maisch, M., Zarfl, C., Muehe, E. M. & Kappler, A.
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Simultaneous minimization of arsenic mobilization and nitrous oxide emission under nitrogen fertilization in paddy soils. World Congress of Soil Sciences
Grimm, H., Drabesch, S., Maisch, M., Joshi, P., Zarfl, C., Muehe, E. M. & Kappler, A.
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Arsenic immobilization and greenhouse gas emission depend on quantity and frequency of nitrogen fertilization in paddy soil. Heliyon, 10(16), e35706.
Grimm, Hanna; Drabesch, Soeren; Nicol, Alan; Straub, Daniel; Joshi, Prachi; Zarfl, Christiane; Planer-Friedrich, Britta; Muehe, E. Marie & Kappler, Andreas
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Nitrous oxide is the main product during nitrate reduction by a novel lithoautotrophic iron(II)-oxidizing culture from an organic-rich paddy soil. Applied and Environmental Microbiology, 91(1).
Grimm, Hanna; Lorenz, Jennifer; Straub, Daniel; Joshi, Prachi; Shuster, Jeremiah; Zarfl, Christiane; Muehe, E. Marie & Kappler, Andreas
