Rhizosphere bacteria affect plant performance and Cd accumulation of poplar (clone ‘I-214’)

"The effects of moderate cadmium soil concentrations on selected physiological parameters of clone ‘I-214’, Populus deltoides × Populus nigra (P. × euramericana (Dode) Guinier), inoculated at root level with Pseudomanos fluorescens and Micosat F Fito were investigated. A pot experiment was held in a screened greenhouse, where plants were subjected to 40 ppm of Cd, against a control treatment. In order to evaluate the effects of plant–microbe interactions, plant growth and physiology and microbial activity were monitored throughout the experiment. Whereas, at the end of the cultivation period, plant tissues were analyzed for Cd content. The Cd amount in tissues exhibited improved Cd absorption in inoculated plants. Heavy metal concentration was high in roots of plants inoculated with P. fluorescens, and in leaves, suggesting a role of microbes in improving metal uptake. The poplar clone ‘I-214’ responded to Cd contamination and microbial inoculation modulating plant growth, gas exchange, and the photosynthetic apparatus; therefore, moderate soil Cd concentration did not inhibit stomatal opening and did not affect negatively photosynthetic functions. Plant-microbe symbiosis increased total removal of Cd, without interfering on plant growth, while improving somewhat physiological behavior. After Cd treatment, microscope observations showed a complete microbial colonization of roots. The Cd concentrations in plant tissues suggested two mechanisms of soil decontamination by microbes: improved Cd accumulation in roots of inoculated plants with phytostabilization and high translocation of Cd to leaves. A detailed proteomic approach combined with multivariate statistical analysis is in progress for deeper insights into the complex cellular processes involved in plant Cd accumulation and to identify key factors regulating Cd phytostabilization and translocation."