Resistance characteristics of Cedrus deodara and Sabina chinensis to heavy metal accumulation under different atmospheric conditions

Cedrus deodara and Sabina chinensis are widely planted in North China. The needles of C. deodara and S. chinensis were sampled in the urban, suburban, and rural districts of Tianjin where the atmospheric conditions are significantly different according to the environmental monitoring results. The Cu, Mn, Zn, and Pb concentrations in the samples were examined via ICP. The resistance indexes, and the malonic aldehyde (MDA), soluble sugar, and free proline levels were also determined. The Pearson coefficients between the resistance indexes and the heavy metal contents were analyzed to compare the two plants abilities to accumulate heavy metal and their resistance characteristics. The results indicated that the heavy metal concentrations had the following significant trend: urban areas > suburban areas > rural areas. In urban areas, the Mn, Zn, and Pb concentrations in C. deodara were as high as 2024.77 mg·kg^? 1, 2397.07 mg·kg^? 1, and 130.07 mg·kg^? 1, significantly higher than in S. chinensis. The Mn, Zn, and Pb concentrations in C. deodara were extremely significantly positively correlated (P < 0.01), but no significant correlations were noted in S. chinensis. The MDA, soluble sugar, and free proline concentrations in C. deodara increased as the heavy metal contents rose along the urban–rural gradient, and were positively correlated with the plant heavy metal contents. They were much higher than the contents in S. chinensis where no differences were noted among the sampling sites. In conclusion, the heavy metal resistance methods used by C. deodara and S. chinensis are different. C. deodara could absorb and accumulate many heavy metals, mainly through increased physiological resistance to stress. In contrast, S. chinensis resistance relied on avoiding contact with the metals and by reducing absorption. These differences are associated with the biological characteristics of C. deodara and S. chinensis, and are closely connected with their coniferous and morphological differences.