The Potential of Paulownia fortunei L. for the Phytoremediation of Pb

Abstract

Pb endangers forest ecological health; phytoremediation is an effective Pb remediation technology. Woody plants with Pb tolerance provided a mechanism for the phytoremediation of Pb. Paulownia fortunei (L.), a fast-growing woody plant, has a good tolerance to Pb. However, its tolerance mechanism is unclear. The results in this study revealed that P. fortunei seedlings can withstand 400 mg·L−1 Pb stress. The quantification of Pb in different P. fortunei tissues showed an increasing trend of accumulation in root > leaf > stem; the transport coefficient and enrichment coefficient decreased with an increase in Pb concentration. The tolerance of P. fortunei to Pb may be related to cell partition and immobilization by the cell wall. Microstructural analysis performed using scanning electron microscopy showed that the absorbed Pb is mainly distributed in cell wall components, and when the concentration of Pb increases, it can be transferred to soluble parts and organelles. The Fourier transform infrared spectrometry results showed that excess hydroxyl groups occurred under Pb stress in the outer epidermis cell walls of roots and leaves adsorbing heavy metals. When the concentration of Pb was over 400 mg·L−1, the growth of P. fortunei was inhibited, the root cell wall was deformed, the plasmolysis occurred in the cauline cell, and the internal leaf capsule was ruptured. Furthermore, antioxidant enzyme activity was significantly reduced. Therefore, P. fortunei can transfer the underground part of Pb to the aboveground part up to the concentration of 400 mg·L−1. This study provides a theoretical basis and technical reference for fully utilizing woody plant resources to restore the ecological environment of forests.