Microalgae enhance the ameliorative effects of organic materials on soil treated by thermal desorption: soil...

After thermal desorption treatment, the soil physical structure became worse, the organic carbon content became lower, and the nutrient was unbalanced. Therefore, improving the properties and nutrient cycling capacity of the treated soil is essential for its ecological restoration. In this study, a incubation experiment was conducted on soil treated by the ex-situ thermal desorption of a polycyclic aromatic hydrocarbon (PAH)-contaminated site. Common organic material amendments (e.g., sheep manure and organic fertilizer) and new biofertilizers (e.g., microalgae) were used to investigate the alterations in soil physicochemical properties, microbial community function and microbial community diversity under eight different treatments. The results showed that microalgae increased the ameliorative effects of organic materials on treated soil. In detail, microalgae decreased the mean particle size of soil and significantly increased the content of clay and silt, and changed its particle size distribution. They also significantly increased the contents of soil total organic carbon (TOC), cation exchange capacity (CEC), total nitrogen (TN), nitrate nitrogen (NO₃^--N), available phosphorus (AP), and available potassium (AK), and reduced soil pH, but with no significant effects on electrical conductivity (EC). Furthermore, microalgae significantly altered the microbial community composition and enhanced soil multifunctionality, especially carbon, nitrogen, and phosphorus cycling. Redundancy analyses showed that TN, TK, and TOC were the primary factors explaining the changes in the composition of the main functional microbial community. The findings of this study provide a theoretical basis for soil fertility restoration and structural reconstruction on soil treated by thermal desorption.