[Characteristics of Mineralization of Organic Carbon and Nitrogen in Paddy Soils in Subtropical Regions and Their Influencing Factors].

The objectives of the present study were to analyze the characteristics and key controlling factors of soil organic carbon and soil organic nitrogen mineralization， in combination with soil basic physicochemical properties and the morphology of Fe and Mn oxides using the random forest and structural equation model， across 24 rice paddy soils sampled from subtropical regions of China. The results showed that the paddy soil organic carbon and soil organic nitrogen mineralization rates varied from 0.67 to 18.21 mg·（kg·d）^-1 and 0.05 to 0.5 mg·（kg·d）^-1， respectively， across sampling sites. Moreover， the paddy soil organic carbon mineralization rates were significantly and positively correlated with nitrogen mineralization rates. The paddy soil organic carbon and soil organic nitrogen mineralization varied significantly among textures， with significantly higher values in clayey paddy soils than in loamy and sandy paddy soils. Soil organic carbon （SOC）， dissolved organic carbon （DOC）， and pH were the main controlling factors of paddy soil organic carbon mineralization. However， the factors influencing soil organic carbon mineralization varied across paddy soil textures. For clayey paddy soils， the key factor was pH， which was negatively correlated with SOC mineralization. For loamy and sandy paddy soils， DOC and active Mn content were the main factors， significantly increasing soil organic carbon mineralization rates. The main influencing factors of paddy soil organic nitrogen mineralization were complexed Fe and pH. For clayey paddy soils， pH and DOC were the key factors， with significantly negative correlations for pH and significantly positive correlations for DOC. For loamy and sandy paddy soils， complexed Fe and complexed Mn were the main controlling factors of the soil organic nitrogen mineralization rate， with significantly positive correlations. In subtropical paddy soils， the clay content and Fe-Mn oxide forms regulated the organic carbon and nitrogen mineralization rates by influencing soil physicochemical properties. Thus， soil texture， soil physicochemical properties， and Fe-Mn oxide forms need to be considered comprehensively in the management of soil organic carbon and soil organic nitrogen in farmland to improve the level of rice soil fertility and sustainable production.