Soil nutrient supply and tree species drive changes in soil microbial communities during the transformation of a multi-generation Eucalyptus plantation

Intensive management of Eucalyptus plantations has caused several social/environmental issues, including the concern over transformation of monoculture plantation cutover area. However, how different transformation patterns of Eucalyptus plantations affect soil microbial communities and their functions is unclear. In this study, the effects of different transformation patterns on structure and potential function of soil bacterial and fungal communities were evaluated. Soil chemical properties and acid phosphatase, urease, and catalase activities were also measured. In the third-generation monoculture Eucalyptus plantations, soil organic matter, nutrient contents, and microbial biomass decreased significantly and the relative abundance of oligotrophic bacteria (Chloroflexi) and symbiotic fungi (ectomycorrhizae) increased significantly compare with CK. However, in the Eucalyptus × Manglietia glauca Blume mixed plantation (E × M) and a Manglietia glauca Blume plantation (Manglietia), soil fertility (e.g., soil organic matter, total nitrogen, total phosphorus, and total potassium) improved, especially in E × M. In addition, soil acid phosphatase (0.30 mg∙g⁻¹∙h⁻¹) and catalase (0.66 mg∙g⁻¹∙h⁻¹) activities and the bacterial gene copies:fungal gene copies ratio (46.70) increased significantly in E × M compared with those in the monoculture plantations. The relative abundance of copiotrophic bacteria (Actinobacteria) and nitrogen cycle-associated bacteria (orders Rhizobiales and Frankiales) increased significantly in E × M. The abiotic factors soil available nitrogen and available zinc were the significant drivers of soil bacterial community structure, whereas the structure of fungal communities was most affected by tree species, in addition to soil pH and available copper. The results indicated that the E × M transformation pattern in the cutover area of Eucalyptus plantations had a significant beneficial effect on the soil fertility. The study also indicated that young plantations with Eucalyptus species have specific requirements for soil available phosphorus, available potassium, and available magnesium. Thus, increasing the supply of these nutrients during plantation development may have a positive effect on the sustainable management of plantations.