Effects of four endophytic bacteria on cadmium speciation and remediation efficiency of Sedum plumbizincicola in farmland soil.

Cadmium (Cd) pollution in farmland soils severely affects agricultural production safety, thereby threatening human health. Sedum plumbizincicola is a Cd and Zn hyperaccumulator commonly used for the phytoremediation of Cd-contaminated soil. This study was aimed to improve the remediation effect of S. plumbizincicola on Cd-contaminated farmland soil and provide a theoretical basis for the enhancement of endophytic bacteria in the repair of Cd-contaminated soil with S. plumbizincicola. Four kinds of endophytic bacteria, namely Buttiauxella, Pedobacter, Aeromonas eucrenophila, and Ralstonia pickettii, were used, and soil culture experiments and pot experiments were conducted to explore the effects of endophytic bacteria on soil Cd speciation and phytoremediation efficiency of Cd-contaminated farmland soils. Under the experimental conditions, after inoculation with endophytic bacteria, the soil pH was effectively reduced, content of weak acid-extracted Cd and oxidizable Cd increased, and content of reducible Cd and residual Cd decreased. Soil Cd activity was increased, and the availability coefficient of soil Cd increased by 1.15 to 6.41 units compared with that of the control (CK2). Compared with CK2, the biomass of S. plumbizincicola significantly increased by 23.23-55.12%; Cd content in shoots and roots of S. plumbizincicola increased by 29.63-46.01% and 11.42-84.47%, respectively; and bioconcentration factor was 2.13 to 2.72 times that of CK2. The Cd removal rate of S. plumbizincicola monocropping was 48.25%. When S. plumbizincicola was planted with inoculating endophytic bacteria, the Cd removal rate in the soil reached 61.18-71.49%, which was significantly higher than that of CK2 (p < 0.05). The treatment with endophytic bacteria activated soil Cd, promoted the growth of S. plumbizincicola, increased its Cd content, and enhanced the phytoremediation of Cd-contaminated farmland soil. Therefore, endophytic bacteria can be used to improve the remediation efficiency of S. plumbizincicola in Cd-contaminated farmland soils.

Analysis of the effect of cadmium stress on root exudates of Sedum plumbizincicola based on metabolomics.

Root exudates are the most direct manifestation of the response of plants changes in the external environment. Therefore, based on non-targeted gas chromatography-time-of-flight mass spectrometry and metabolomics, the response of Sedum plumbizincicola root exudates to Cd stress was used to reveal the possible mechanism of resistance to or accumulation of Cd. The results showed that Cd significantly changed the composition and contents of S. plumbizincicola root exudates. A total of 155 metabolites were identified in S. plumbizincicola root exudates, among which 33 showed significant differences under Cd stress, including organic acids, amino acids, lipids, and polyols. Cd stress suppressed organic acid metabolism and lipid metabolism in S. plumbizincicola and significantly affected amino acid metabolism. There were 16 metabolic pathways related to Cd stress, among which arginine and proline metabolism, valine, leucine, and isoleucine biosynthesis, glycine, serine, and threonine metabolism, glutathione metabolism, and purine metabolism were the key pathways with the highest correlation, and were closely related to the stress resistance of S. plumbizincicola.