Molybdenum Bioavailability and Asymbiotic Nitrogen Fixation in Soils are Raised by Iron (Oxyhydr)oxide-Mediated Free Radical Production

• Published in: Environmental science & technology Vol. 55; no. 21; pp. 14979 - 14989
• Main Authors: Yu, Guang-Hui, Kuzyakov, Yakov, Luo, Yu, Goodman, Bernard A, Kappler, Andreas, Liu, Fei-Fei, Sun, Fu-Sheng
• Format: Journal Article
• Language: English
• Published: Easton American Chemical Society 02.11.2021
• Subjects: Abundance; Agricultural ecosystems; Bioavailability; Biogeochemical Cycling; Chemical reactions; Cycles; Fertilization; Free radicals; Genes; Goethite; Hematite; Hydroxyl radicals; Iron; Manures; Micronutrients; Microorganisms; Molybdenum; Nanoparticles; NifH gene; Nitrogen; Nitrogen fixation; Nitrogenase; Nitrogenation; Oxides; Soils; hydroxyl radical; iron (oxyhydr)oxide; molybdenum bioavailability; reactive oxygen species; stable isotope probing; Fenton reaction; nitrogen fixation; long-term fertilization
• ISSN: 0013-936X; 1520-5851
• DOI: 10.1021/acs.est.1c04240

Nitrogen (N) fixation in soils is closely linked to microbially mediated molybdenum (Mo) cycling. Therefore, elucidating the mechanisms and factors that affect Mo bioavailability is crucial for understanding N fixation. Here, we demonstrate that long-term (26 years) manure fertilization increased microbial diversity and content of short-range ordered iron (oxyhydr)­oxides that raised Mo bioavailability (by 2.8 times) and storage (by ∼30%) and increased the abundance of nifH genes (by ∼14%) and nitrogenase activity (by ∼60%). Nanosized iron (oxyhydr)­oxides (ferrihydrite, goethite, and hematite nanoparticles) play a dual role in soil Mo cycling: (i) in concert with microorganisms, they raise Mo bioavailability by catalyzing hydroxyl radical (HO•) production via the Fenton reactions and (ii) they increase Mo retention by association with the nanosized iron (oxyhydr)­oxides. In summary, long-term manure fertilization raised the stock and bioavailability of Mo (and probably also of other micronutrients) by increasing iron (oxyhydr)­oxide reactivity and intensified asymbiotic N fixation through an increased abundance of nifH genes and nitrogenase activity. This work provides a strategy for increasing biological N fixation in agricultural ecosystems.