Physiological Responses of Populus cathayana and Salix babylonica to Combined Stress of Diesel Fuel and Sr2+ Stress in Soil

Abstract

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.

Keywords: Populus; Salix; Sr2+ stress; combined stress; diesel stress; tree physiology.

Figure 1

Sr²⁺ enrichment and correlation analysis between different tissues of female and male seedlings of P. cathayana and S. babylonica. Sr²⁺ enrichment in root, stem, and leaf tissues of P. cathayana (A) and S. babylonica (B); correlation coefficients between different treatment groups of P. cathayana (C) and S. babylonica (D).

Figure 2

Activities of SOD (A), APX (B), POD (C), and contents of MDA (D) of P. cathayana and S. babylonica under different treatments. Values are expressed as means ± SE (n = 5). Values followed by the same letter in the same column are not significantly different (p < 0.05). ***: p < 0.001; **: p < 0.01, *: p < 0.05.

Figure 3

Contents of proline (A) and sugar (B) of P. cathayana and S. babylonica under different s treatments. Values are expressed as means ± SE (n = 5). Values followed by the same letter in the same column are not significantly different (p < 0.05). ***: p < 0.001;**: p < 0.01, *: p < 0.05.

Figure 4

Activity of AKP (A), ACP (B), Ure (C), and sucrase (D) in P. cathayana and S. babylonica with different treatments. Values are expressed as means ± SE (n = 5). Values followed by the same letter in the same column are not significantly different (p < 0.05). ***: p < 0.001;**: p < 0.01, *: p < 0.05.

Figure 5

Correlation analysis of each index under different treatments of female (a) and male (c) for S. babylonica, and female (b) and male (d) for P.cathayana.