About the Seminar:
The study of soil organic matter (SOM) degradation remains difficult to understand due to the heterogeneity and polydispersity of soils which lead to complex transformation pathways during decomposition. Wetland ecosystems act as a vital global carbon (C) sink, making the understanding of organic matter transformation under anoxic conditions necessary to understanding the global C-cycle. Many studies focus on the role microorganisms play in mineralizing SOM; however, mineral-controlled SOM oxidation has recently become a focus of understanding C-mineralization, a process which greatly affects our predictions of climate change. Birnessite (δ-MnO2), a manganese oxide naturally abundant in soils, has been proven to be an important mineral in C-cycling as it is highly redox active (E°=+1.23), significantly higher than other inorganic soil oxides. The study Oxygen Limitation Accelerates Regeneration of Active Sites on a MnO2 Surface: Promoting Transformation of Organic Matter and Carbon Preservation by Wang et al. 2022 investigated how complex mixtures of SOM components react over time with birnessite in oxic versus anoxic systems and reported a higher degree of SOM transformation within the anoxic system (79.8% SOM reduction) versus oxic conditions (69.8% SOM reduction). The authors proposed unprecedented mechanisms of the generation of reactive oxygen species (ROS) from the birnessite surface which can induce additional SOM transformations. However, within the anoxic systems, the authors theorized that the ROS were generated from lattice-bound oxygen within the birnessite structure itself. This can decay the structure of birnessite, suggesting a temporal limitation of this highly reactive system, but only in oxygen limiting environments. These findings provide novel insights of birnessite-mediated SOM mineralization rates and longevity into anoxic environmental systems such as wetlands.