Effects of heavy metals Cu, Ni, and Pb on seed germination characteristics of Halogeton glomeratus under salinity and drought stress

This study assessed the effects of three major soil heavy metal pollutants (Cu, Ni, and Pb) and salinity, drought (100.0 mmol·L^–1 NaCl + 2.0% PEG) on seed germination characteristics of the halophyte Halogeton glomeratus to better understand the stress tolerance of this species. Compared to the control treatment (100.0 mmol·L^–1 NaCl + 2.0% PEG), lower Cu²⁺ concentrations significantly promoted (P < 0.05) the germination of H. glomeratus seeds even under salinity and drought stress, whereas lower Ni²⁺ and Pb²⁺ concentrations showed little effect on seed germination. However, higher Cu²⁺, Ni²⁺, and Pb²⁺ concentrations inhibited seed germination. Seedling length, fresh weight, dry weight, and root activity presented different downward trends. Plant tissue ion content remained low under stress induced by low metal concentrations but increased rapidly under stress induced by high metal concentrations. In cluster analysis, the metal concentrations were grouped into two categories as 1.0 mmol·L^–1 Cu²⁺ and Ni²⁺ and 3.0 mmol·L^–1 Pb²⁺. In addition, principal component analysis revealed that germination percentage and germination energy showed the highest contribution rate under Cu²⁺ and Ni²⁺ treatments and dry weight showed the highest contribution rate under Cd²⁺ treatment. These results indicate that salinity, drought (100.0 mmol·L^–1 NaCl+2.0% PEG) and low heavy metal concentrations (1.0 mmol·L^–1 Cu²⁺ or Ni²⁺ and 3.0 mmol·L^–1 Pb²⁺) had little effect on the germination and seedling growth of H. glomeratus. Germination percentage and germination energy can be used for evaluating the tolerance of H. glomeratus to Cu and Ni and dry weight to evaluate the tolerance of H. glomeratus to Pb during the germination period.