Abstract: Industrialization and the rapid growth of economies have caused severe environmental pollution, which might impact the survival of sensitive species. In this study, we investigated the defense responses of two common mosses with varying anti-haze capacities, Hypnum callichroum and Homomallium incurvatum, in response to simulated haze pollution. Photoprotection and antioxidant mechanisms of both mosses were measured immediately after the first exposure to the haze treatment, followed by the initial recovery stage and again after exposure to secondary stress and secondary recovery. Haze exposure caused severe oxidative stress and photodamage in both H. callichroum and H. incurvatum. Metabolic processes such as photorespiration, the ascorbate–glutathione cycle and secondary metabolism—which play roles in defense responses—were significantly activated in both moss species after haze treatment. During the recovery following haze stress, H. callichroum exhibited a significant stress memory response, as evidenced by the greater accumulation of several memory substances, including xanthophylls and phenolic acids. However, H. incurvatum did not exhibit a strong stress memory response, which might explain its relatively inferior anti-haze capacity in the natural environment.

Key words: haze, stress memory, environmental pollution, moss, resistance