Endophyte inoculation enhanced microbial metabolic function in the rhizosphere benefiting cadmium phytoremediation by Phytolacca acinosa

Microbial metabolic activities in rhizosphere soil play a critical role in plant nutrient utilization and metal availability. However, its specific characteristics and influence on endophyte assisted phytoremediation remains unclear. In this study, an endophyte strain Bacillus paramycoides (B. paramycoides) was inoculated in the rhizosphere of Phytolacca acinosa (P. acinosa), and microbial metabolic characteristics of rhizosphere soils were analyzed using Biolog system to investigate how they influence phytoremediation performance of different types of cadmium contaminated soil. The results indicated that endophyte B. paramycoides inoculation enhanced bioavailable Cd percentage by 9–32%, resulting in the increased Cd uptake (32–40%) by P. acinosa. With endophyte inoculation, the utilization of carbon sources was significantly promoted by 4–43% and the microbial metabolic functional diversity increased by 0.4–36.8%. Especially, B. paramycoides enhanced the utilization of recalcitrant substrates carboxyl acids, phenolic compounds and polymers by 48.3–225.6%, 42.4–65.8% and 15.6–25.1%, respectively. Further, the microbial metabolic activities were significant correlated with rhizosphere soil microecology properties and impact phytoremediation performance. This study provided new insight into the microbial processes during endophyte assisted phytoremediation.