Highly promoted phytoremediation with endophyte inoculation in multi-contaminated soil: plant biochemical and rhizosphere soil ecological functioning behavior

Rhizosphere soil ecological functioning behavior is of critical importance for regulating phytoremediation efficiency during microbial-assisted phytoremediation for multi-heavy metal–polluted soils. In this study, Trifolium repens L. and its endophyte Pseudomonas putida were used to investigate the ecological responses of the microbe-plant-soil system in Cd, Cr, and Pb co-contaminated soil. The results showed that endophyte Pseudomonas putida significantly increased plant biomass by 22.26–22.78% and phytoremediation efficiency by 29.73–64.01%. The increased phytoremediation efficiency may be related to the improvement of photosynthetic pigment content and antioxidant enzyme activities in leaves and the enhancement of rhizosphere soil ecological functioning. With endophyte application, soil nutrient content was significantly increased and heavy metal bioavailability was enhanced that residual fraction was reduced by 3.79–12.87%. Besides, the relative abundance of ecologically beneficial rhizobacteria such as Bacteriovorax and Arthrobacter was increased by 3.04–8.53% and 0.80–1.64%, respectively. Endophyte inoculation also significantly increased all the functional genes involved in cellular processes, genetic information processing, environmental information processing, and metabolism. This study indicated that the application of endophytes has a positive effect on the biochemical responses of Trifolium repens L. and could significantly improve rhizosphere ecological functioning in multi-heavy metal contamination, which provided clear strategies for regulating phytoremediation.