Mechanism insights into amendments enhanced dendroremediation for Cd and Zn-polluted soil: Bacterial co-occurrence networks’ complexity and stability

Soil amendments enhance phytoremediation utilizing trees, have attracted considerable attention because of their low cost, great benefits and huge potential. It’s demonstrated that amendments facilitate the metal immobilization via adjusting soil pH and metal availability, while the underlying mechanism on amendments improving phytoremediation efficiency remains unclear. In our previous studies, the phytoremediation efficiency of Quercus spp. for Cd and Zn was improved by application of soil amendments in a three-year field trial located in Hangzhou, China. Here, we collected the soil samples from the above mentioned experiment and further compared the characteristics of the rhizosphere bacterial community of Quercus texana and Quercus fabri amended with rice straw biochar, palygorskite, and a combination of rice straw biochar and palygorskite in Cd- and Zn-contaminated soils. There were no significant differences in bacterial diversity between the Q. texana and Q. fabri, which were characterized by a high and low accumulation of heavy metals. However, rhizosphere bacterial network of both species exhibited significant responses to the different soil amendments. Combined biochar increased the complexity and stability of bacterial networks, which was manifested mainly as an increase in network cohesion, negative:positive cohesion, and robustness. Partial least squares path modeling demonstrated that network stability was directly influenced by complexity (path coefficient = 0.551, p < 0.05) and keystone taxa (path coefficient = -0.29, p < 0.05), where keystone taxa can serve as a significant predictor variable for network stability. Furthermore, network complexity and stability were significantly correlated with heavy metal accumulation in Quercus spp., suggesting potential linkages between microbial network properties and phytoremediation efficiency. Together, the results emphasize that combined biochar enhances the complexity and stability of rhizosphere bacterial network, ultimately improving phytoremediation efficiency and biomass. Lower network stability in the rice straw biochar and palygorskite treatments may pose ecological risks. These novel findings provide important insights into optimizing amendments to improve phytoremediation efficiency by affecting rhizosphere microbial interactions.