Abstract
Heavy metal toxicity affects germination, seedling growth, and other physiological processes in plants. To assess the toxic effects of heavy metals on the seed germination and seedling growth of Pinus roxburghii, we tested lead (Pb) and cadmium (Cd) at multiple concentrations ranging from 30-180 mg/L in both heterogeneous and homogeneous environments. The results showed that all seeds germinated regardless of Pb and Cd concentrations and environmental conditions, and the final germination percentage (GP) remained unchanged. Under different Pb and Cd stress levels, the seedlings grown under homogeneous conditions exhibited a higher stress tolerance index (STI) in morphological traits than those grown in heterogeneous environments. Pb and Cd also affected physiological indicators, their various concentrations promoted free proline in both environmental conditions. Sugar content in seedlings grown in heterogeneous environments ranged from 47.82% to 6.52% with Pb and 58.69 to 4.34% with Cd. In seedlings grown in homogenous environments, sugar content ranged from 45.71% to 5.71% with Pb and 37.14 to 2.85% with Cd. Chlorophyll a/b and carotenoids exhibited declining trends, with chlorophyll 'a' declining more than chlorophyll 'b'. This research indicates that P. roxburghii can be successfully used for plant restoration. It provides insights into potential hyper-tolerance mechanisms and can be utilized as a potential tree for roadside plantations to alleviate air pollution.