Abstract: Mosses, as sensitive environmental indicators, have been widely used in the monitoring of heavy metal pollution. Syntrichia caninervis, Bryum argenteum, and Plagiomnium acutum that distributed in Northwest China were used as materials in a laboratory Pb stress experiment. We compared the differences of chlorophyll content, osmotic adjustment substance content and antioxidant enzyme activity of mosses for their responses to different Pb concentrations, aiming to provide scientific basis for monitoring mosses in Northwest China. The results showed that chlorophyll content of B. argenteum and P. acutum had a stress effect on lower concentrations of Pb stress (1-5 mmol·L^-1), while S. caninervis showed consistent inhibition under different Pb concentrations (1-10 mmol·L^-1). The chlorophyll a/b values of the three species were significantly reduced by Pb stress. Under Pb stress, the three moss species would produce free proline, soluble protein and soluble sugar to regulate osmotic balance, but the increase rates varied among different treatments. High Pb concentration (10 mmol·L^-1) caused serious toxicity to mosses, leading to a significant decrease in the content of osmotic adjustment substances. The malondialdehyde (MDA) content of mosses increased significantly with increasing Pb concentration. The activities of superoxide dismutase, peroxidase and catalase were stimulated by low Pb concentration (1-5 mmol·L^-1) and inhibited by high Pb concentration (10 mmol·L^-1). The sensitivity of the three moss species to Pb stress was as follows: S. caninervis>B. argenteum>P. acutum. Our results suggested that S. caninervis could be used as a sensitive indicator for Pb pollution. P. acutum, which has strong Pb tolerance, had the potential for bioremediation of Pb pollution. By comparing the changes of different physiological indices, it was found that the content of MDA had a single concentration dependence on Pb stress, which could be used as a biomarker to detect Pb pollution.

Key words: mosses, heavy metal pollution, physiological characteristics, Pb stress.