Towards a better understanding of the role of Fe cycling in soil for carbon stabilization and degradation

Abstract

AbstractIron (Fe) minerals play an important role in stabilizing soil organic carbon (SOC). Fe-mediated SOC protection is mainly achieved through adsorption, co-precipitation, or aggregation. However, newly emerging evidence indicates that the electron transfer role of Fe exerts a crucial influence upon SOC turnover. In this review, we address the pathways of Fe mineral-associated soil organic carbon (Fe-SOC) formation and decomposition, and summarize the Fe-mediated biogeochemical, including redox reactions, and physical processes that control SOC cycling. The reduction of Fe can release SOC from Fe-SOC coprecipitates and Fe(III) cemented micro-aggregates, with the process also releasing CO2 from the metabolic coupling of SOC oxidation and Fe reduction. The abiotic oxidation of Fe(II) by oxidants can also oxidize SOC to produce CO2 due to reactive oxygen species production. Therefore, the functional roles of Fe on SOC sequestration may be a double-edged sword, and these processes are rarely explored concurrently. We conclude that the roles of Fe minerals in SOC stability depend on the properties of the Fe mineral, edaphic properties, and anthropogenic influence. We highlight knowledge gaps and promising directions of future research in redox-dynamic environments to optimize carbon storage in soil. Graphical Abstract