Heavy metal pollution and soil salinization harm human health and the environment. Phytoremediation is a widely accepted soil decontamination method, with woody plants being particularly effective due to their large biomass and extensive root systems. In this study, we identified and cloned PsnMLP328 from Populus simonii x P. nigra and demonstrated its role in mitigating salt and cadmium stress. PsnMLP328 expression was up-regulated under both stress conditions, and its overexpression in tobacco enhanced resistance to these stresses, albeit through distinct mechanisms. Transgenic plants exhibited increased Cd2+ uptake and a higher biomass, alleviating Cd2+-induced growth inhibition. Additionally, PsnMLP328 boosted proline content, chlorophyll levels, and antioxidative enzyme activities (POD, SOD) under Cd2+ stress, likely by protecting cells from oxidative damage. Expression analysis revealed that PsnMLP328 down-regulated the cadmium transporter Nramp2 while up-regulating YSL2 (another cadmium transporter) and potassium channels (AKT1 and AKT2/3), suggesting its role in modulating K+ and Cd2+ homeostasis. These findings indicate that PsnMLP328 enhances tobacco resistance to salt and cadmium stress, particularly the latter. This study is the first to elucidate the function of poplar MLP family genes under salt and cadmium stress, advancing our understanding of MLP gene roles in heavy metal stress and offering new insights for remediating salinized and heavy metal-contaminated soils.

Diesel spills and nuclides pollution cause global ecosystem and human health problems. The remediation of contaminated soil using woody plants has received considerable attention. Differences in plant species and sex can lead to differences in tolerance to various stressors. We aimed to investigate the response of male and female seedlings of Populus cathayana and Salix babylonica to diesel and Sr2+ stress and to compare the enrichment characteristics of Sr2+ in trees. Male and female seedlings of P. cathayana and S. babylonica were treated with diesel fuel and 0, 10 (low), and 100 (high) mg Kg(-1) of Sr2+. Results showed that P. cathayana and S. babylonica had good enrichment characteristics and tolerance. S. babylonica had a more robust tolerance and ability to remediate contaminated soil than P. cathayana. The defense mechanisms of both female seedlings in response to stress were similar, while males showed different defense strategies. Male trees had higher Sr2+ enrichment capacity, antioxidant enzymes, soil enzyme activity, and soluble matter content, indicating that males had higher tolerance capacity than females. Under diesel stress alone, the reduced photosynthetic rate of male seedlings of P. cathayana was mainly limited by stomatal factors, and their photosynthetic system was more tolerant to diesel. POD and APX activities, as well as alkaline phosphatase and urease activities in the soil, were significantly higher in S. babylonica seedlings than in P. cathayana, indicating that S. babylonica seedlings were more resistant to diesel pollution. At low concentrations of the Sr2+ complex, diesel and Sr2+ showed antagonistic effects in reducing the damage caused by stress. As the Sr2+ concentration increased, damage to the plants manifested primarily through synergistic enhancement. The results of this study provide a scientific basis for the remediation of diesel fuel and nuclides contaminated soils using woody plants.

Both acid and alkaline purple soils in China are increasingly affected by Cd contamination. The selection of fastgrowing trees suitable for remediating different soil types is urgent, yet there is a severe lack of relevant knowledge. In this study, we conducted a controlled pot experiment to compare the growth, physiology, and Cd accumulation efficiency of two widely recognized poplar species, namely Populus deltoides and P. x canadensis, under Cd contamination (1 mg kg-1) in acid and alkaline purple soils. The objective was to determine which poplar species is best suited for remediating different soil types. Our findings are as follows: (1) the total biomass of both poplars remained largely unaffected by Cd pollution in both soil types. Notably, under Cd pollution, the total biomass of P. deltoides in acid purple soil was 1.53 times greater than that in alkaline purple soil. (2) Cd pollution did not significantly induce oxidative damage in the leaves of either poplar species in both soil types. However, in acid purple soil, Cd contamination led to a 21% increase in NO3- concentration and a 44% increase in NH4+ concentration in P. x canadensis leaves, whereas in alkaline purple soil, it led to a 59% increase in NH4+ concentration in P. deltoides leaves. (3) Cd concentrations in all root orders of P. x canadensis were significantly higher than those in P. deltoides, especially in the first three root orders, under alkaline purple soil. The total Cd accumulation by P. x canadensis in Cd-polluted alkaline purple soil was 2.18 times higher than that in Cdpolluted acid purple soil, a difference not observed in P. deltoides. (4) redundancy analysis indicated that the sequestration effect of higher soil organic matter on Cd availability in acid purple soil was more pronounced than the release effects caused by lower pH. In conclusion, P. x canadensis is better suited for remediating alkaline purple soil due to its higher capacity for Cd uptake, while P. deltoides is more suitable for remediating Cdcontaminated acid purple soil due to its better growth conditions and greater Cd enrichment capability.