The contamination of toxic heavy metals was a major issue of concern in the last century. A fast-growing metal-accumulating woody plant is a promising approach for the remediation of toxic heavy metal. In this study, the transportation of heavy metals (Pb, Zn, Cu, and Cd) in Paulownia fortunei cultivated in lead-zinc slag amended with different mass ratios of peat (CK: 0; T1: 10%; T2: 20%; T3: 30%) was investigated, as well as the subcellular distribution of Pb, Zn, Cu, and Cd in Paulownia fortunei. The results showed that the accumulation content of Pb, Zn, Cu, and Cd in Paulownia fortunei were increased with peat amendment, which was in the range of 4.216 ∼ 6.853, 20.905 ∼ 23.017, 1.898 ∼ 2.572, and 0.530 ∼ 0.616 mg/pot, respectivly. The experimental group with 30% dose of peat showed the best performance on the accumulation content of Pb, Zn, Cu, and Cd, with increase rates (compared to control) of 4.088, 10.573, 1.360, and 0.294 mg/pot, respectively. The bioconcentration, translocation and transfer quantity factor of Pb, Zn, Cu, and Cd were less than 1. Fixation of cell wall and compartmentalization of vacuolar appeared to play an important role in reducing the toxicity of Pb, Zn, Cu, and Cd.

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.

Carbon source deficiency is a critical bottleneck limiting nitrogen removal efficiency and exacerbating nitrous oxide (N₂O) emissions in constructed wetlands (CWs) treating low carbon-to-nitrogen (C/N) tailwater. Biodegradable plastics and wetland plant residues are the autochthonous carbon sources in water; however, the denitrification enhancement effect of their composite remains unclear. Herein, the PHBV/reed composite was prepared, its performance in CWs was evaluated. Results showed that, the presence of PHBV/reed significantly enhanced the NO₃⁻ removal efficiency to 89.98%, while simultaneously reducing N₂O, CH₄, and CO₂ emissions by 50–64%. Mechanistically, the composite released DOM rich in readily biodegradable components, which selectively enriched key denitrifying genera (Dechloromonas and Hydrogenophaga). This shift enhanced the electron transport system activity (ETSA) by 78.87%. Metagenomic analysis revealed that the PHBV/reed composite activated glycolysis and the tricarboxylic acid cycle, promoting NADH/ATP synthesis, with the generated electrons preferentially allocated to nitrate reduction. Furthermore, the composite mitigated N₂O emissions through the way of down-regulating norB/norC genes (EC 1.7.2.5) to suppress N₂O production, and up-regulating nosZ gene (EC 1.7.2.4) to enhance N₂O consumption. This study unveils a novel paradigm of in-situ denitrification driven by autochthonous carbon sources in CWs, offering a green and sustainable technological solution for low C/N tailwater treatment.