Improved the phytoremediation efficiency of <i>Ricinus communis</i> L. in Cu/Cd contaminated soil via endophytes inoculation

The application of <i>Ricinus communis</i> L. on remediation of heavy metal-polluted soil shows significant potential due to its advantages of large biomass, high resistance to heavy metals and high economic value, etc. To further enhance phytoremediation efficiency, eight plant growth-promoting endophytic bacteria (TR4, TR8, TR16, TR18, TR21, YL1, YS3 and YS5) were used to investigate the effect of inoculation on <i>R. communis</i> growth and Cu/Cd accumulation. The results showed that inoculation of strain TR16, TR18, TR21, YS3, and YS5 significantly increased plant biomass by 20.0%-39.9%. Except for strain YL1 and TR4, other six strains increased Cu and Cd concentration in plant tissues to varying degrees, as well as total metals uptake. Total uptake of Cu and Cd were enhanced by 15.8%-71.8% and 20.8%-85.4%, respectively. TR16, TR18 and TR21 treatments got the greatest improvement. Inoculation of endophytic bacteria also promoted the absorption of P, Fe, and Mg by plants. Consequently, inoculating TR16, TR18, TR21 and YS3 effectively boosted the phytoextraction efficiency of Cu/Cd by increasing plant biomass, and enhanced heavy metal concentration in different <i>R. communis</i> tissues. These findings provided basis for strengthening <i>R. communis</i> phytoremediation efficiency in Cu/Cd-contaminated soil using plant growth-promoting endophytic bacteria.