Endophyte inoculation redistributed bioavailable Cd and nutrient in soil aggregates and enhanced Cd accumulation in Phytolacca acinosa.

Plant growth and heavy metal (HM) accumulation is affected by heavy metal bioavailability and nutrient content in soil aggregates during endophyte-assisted phytoremediation. In this study, we evaluated the influence of endophytes inoculation on P. acinosa HM accumulation and soil aggregate physicochemical properties and explored the correlation among them. Endophyte inoculation increased the plant growth and Cd accumulation by 7.95-25.13% and 3.27-19.22%, respectively and the soil aggregate was redistributed with a decrease of 1.88-5.41% of the clay fraction. The available nitrogen, phosphorus and potassium, and organic matter in macro-aggregate and micro-aggregate were significantly improved with endophyte inoculation. In addition, compared to the no inoculation group, endophytes inoculation enhanced the bioavailability of Cd in macro-aggregates by 4.92-15.00% and in micro-aggregate by 0-9.37%. Both multiple linear regression analysis and the structural equation modeling (SEM) analysis showed that the Cd accumulation in P. acinosa was mainly depended on the Cd bioavailability in macro-aggregates and micro-aggregates. In general, this study helped to improve our understanding of soil aggregate HM bioavailability and nutrient content distribution characteristics under endophyte inoculation, which could further explain the mechanisms of endophytes in plant growth promoting and HM accumulation improving.