Influence mechanisms of iron, aluminum and manganese oxides on the mineralization of organic matter in paddy soil

The mineralization of soil organic matter (SOM) is closely related to the emission of greenhouse gas into atmosphere and the stability of organic carbon in soil. The influence of minerals on SOM mineralization in the specific soil received very few attentions. The influence characteristics and potential mechanisms of oxides on the mineralization of SOM in the paddy soil were observed in this study by incubating soil with the addition (dosage: 10 g kg⁻¹) of prepared gibbsite, goethite, ferrihydrite or birnessite for 60 days. A sequence control treatment (753 mg CO₂–C kg⁻¹) > goethite treatment (656 mg CO₂–C kg⁻¹) ≈ gibbsite treatment (649 mg CO₂–C kg⁻¹) > birnessite treatment (529 mg CO₂–C kg⁻¹) > ferrihydrite treatment (441 mg CO₂–C kg ⁻¹) was found in the cumulative amount of released CO₂ in 60 days of incubation. Oxides especially ferrihydrite significantly decreased the content of dissolved organic matter (DOM) but tended to increase the content of microbial biomass carbon (MBC). The molecular structure of DOM in the paddy soil was simplified by gibbsite, ferrihydrite and birnessite after the incubation. Oxides especially birnessite and ferrihydrite reduced soil pH and the content of soil available N but increased soil redox potential (Eh). All examined oxides especially Fe oxides enhanced soil bacterial abundance but only birnessite significantly affected bacterial composition at phyla level. The stimulation on the immobilization and/or microbial assimilation of labile organic carbon, the modulation on soil basic properties (available N, pH, Eh), and the decrease of the relative abundance of some decomposing bacteria phyla such as Actinobacteria were the potential pathways of oxides in decreasing SOM mineralization.