Pb(II) sensitivity thresholds in two model plant species: germination, morphological abnormalities, and implications for sustainable soil management

Lead contamination of soils remains a significant environmental challenge, threatening soil quality, ecosystem functioning, and the long-term sustainability of agricultural systems. This study investigated the influence of Pb(II) on seed germination and early seedling growth in cress (Lepidium sativum) and wheat (Triticum aestivum), exposed to concentrations ranging from 10 to 500 mg/L. Germination percentage, the frequency of normal and abnormal seedlings, root, shoot, and leaf development, as well as toxicity and tolerance indices were evaluated. We aimed at a comparative analysis of two plant species with distinct physiological characteristics under the same experimental conditions, allowing the identification of species-specific responses to lead exposure. While germination rates remained high throughout the experiment (approximately 95%), increasing Pb(II) concentrations resulted in a pronounced rise in the proportion of abnormal seedlings. In cress, the percentage of abnormal seedlings increased from 21% to 63%, whereas in wheat it reached 50% at the highest concentration tested. Growth inhibition was more evident in certain plant organs, with cress shoots exhibiting the greatest sensitivity, reflected by a toxicity index of 40% at 500 mg/L. In contrast, wheat roots showed notable reductions only at the highest lead concentration, with a toxicity index of 30%. The results demonstrate clear differences in lead tolerance between the two species and highlight the need to assess multiple growth parameters beyond germination. Both cress and wheat proved to be suitable bioindicator species for assessing the phytotoxic effects of lead-contaminated environments, supporting rapid ecotoxicological screening and early detection of contamination risks within sustainable soil management practices.