Comparisons on the lead-tolerance and physiological response of different Hydrangea paniculata cultivars to lead stress

Abstract

The rising lead (Pb) pollution highlights the need for remediation methods, with phytoremediation being an effective approach. Hydrangea paniculata, known for its specific capacity to absorb Pb, represents a promising option for phytoremediation Pb-contaminated soil. However, studies about Pb-tolerance among different cultivars and their physiological responses remain limited. Here, H. paniculata cultivar 'Polar Bear' was primarily treated with different concentrations of Pb(NO₃)₂ to identify the optimal treating level. Subsequently, 17 H. paniculata cultivars were exposed to the selected Pb(NO₃)₂ concentration to evaluate Pb-tolerance by measuring Pb content and translocation factors, following by principal component, correlation, variance, and cluster analyses. Thereafter, two representative cultivars with the strongest ('Little Lemon') and weakest ('Polar Bear') Pb-tolerance were selected to assess physiological responses to Pb stress. The results showed that 1.0 mmol·L⁻¹ Pb(NO₃)₂ is the optimal concentration. Furthermore, the 17 cultivars were classified into three categories: three cultivars exhibited strong tolerance, six showed moderate tolerance, and eight demonstrated weak tolerance. Additionally, the increased Pb content in leaves could serve as an indicator of Pb-tolerance. Compared to 'Polar Bear', 'Little Lemon' displayed significantly enhanced activities of antioxidant enzymes including SOD, POD, and CAT. These results indicated that Pb tolerance varies substantially across H. paniculata cultivars, and that antioxidant enzymes likely play a key role in this tolerance mechanism. This study not only suggests ideal cultivars for the phytoremediation of Pb-contaminated soil, but also lays a physiological foundation for further exploration of Pb-tolerant mechanism in H. paniculata.