Evaluating the tolerance of Barringtonia acutangula seedlings to combined lead and chromium stress

Urban industrialization has made lead (Pb) and chromium (Cr) ubiquitous pollutants, posing ecological threats. However, the tolerance of Barringtonia acutangula (L.) Gaertn, a widely used landscape plant, to these metals remains unclear, thus limiting its evaluated potential for phytoremediation and greening on contaminated sites. A pot experiment was conducted to investigate the tolerance mechanism by exposing seedlings to gradient concentrations of single (Pb or Cr) and combined Pb-Cr stresses, and analyzing growth, physiological responses, and metal uptake/translocation characteristics. The results showed that:(1) Under single or combined stress, plant height, ground diameter, activities of superoxide dismutase (SOD) and peroxidase (POD), contents of soluble protein (SP) and soluble sugar (SS), all showed an initially increased and then decreased with increasing heavy metal concentrations. In contrast, the values of free proline (Pro), malondialdehyde (MDA), and relative electrical conductivity (REC) gradually increased. (2) As the concentrations of Pb and Cr increased, the contents of Pb and Cr in roots, stems, and leaves rose. However, under combined treatment, the accumulation of heavy metals in tissues decreased due to antagonistic effects. (3) B. acutangula demonstrated a strong root enrichment capacity for Pb and Cr but a weak translocation ability. Under combined Pb-Cr stress, the two metals exhibited primarily antagonistic interactions. (4) Membership function evaluation indicated that the P2 treatment group (Pb 200 mg·kg-¹) had the highest comprehensive tolerance value (D), suggesting that B. acutangula exhibits strong adaptive potential when Pb concentration does not exceed 200 mg·kg-¹.