Phenolic Acid Concentration and Adsorption in the Soil of Monoculture Eucalyptus and Acacia Mangium Plantations Versus Species Mixtures in Subtropical Forests

Purpose: This study explores the accumulation of phenolic acids in soil within monoculture plantations of Eucalyptus, Acacia mangium, contrasting with mixed species plantations containing both species, across various seasons. The research aims to provide insights into how different plantation types and species compositions influence the presence and levels of phenolic acids in soil. Methods: Soil phenolic acid concentrations were determined using HPLC, analyzing seven phenolic acids, including p-hydroxybenzoic, ferulic, coumaric, and benzoic acids. The kinetic adsorption experiments evaluated phenolic acid adsorption rates and quantities across various soil types. An adsorption kinetic model compared these concentrations between monoculture and mixed forest soils. Results: Our findings showed that plantation types, soil positions and seasons significantly impact phenolic acid accumulation. Non-rhizosphere soil in monoculture Eucalyptus plantations exhibited the highest phenolic acid concentration an average (32 µg g^-1) across all seasons compared to mixed species plantations. Conversely, the rhizosphere soil of monoculture Acacia mangium displayed the highest content, reaching 71 µg g^-1 in March. Notably, four phenolic acids (p-hydroxybenzoic, ferulic, coumaric, and benzoic acids) varied significantly between monoculture and mixed forests. Additionally, adsorption kinetic studies revealed that monoculture Eucalyptus and Acacia mangium soils had higher adsorption capacity compared to mixed species soils. The application of Elovich model yielded the best fit for ferulic and coumaric acids (R² > 0.45). Conclusion: Mixed species plantations of Eucalyptus and Acacia mangium significantly influence soil phenolic acid levels compared to monoculture forests and induce alterations in soil adsorption characteristics for phenolic acids, potentially impacting soil fertility and productivity.