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A simulated wetland experiment was used to investigate the effect of thallium (Tl) accumulation on the growth of Arundo donax L., its photosynthetic characteristics and its antioxidant enzyme activities. Tl accumulated in the order of stems, leaves, roots and increased gradually with increasing Tl concentrations (from 0 to 2.5 µg L-1). Moderate Tl applications (from 0.2 to 2.5 µgL-1) increased the rate of both photosynthesises (Pn) and transpiration (Tr), as well as catalase and peroxidase activity. Tl significantly affected stomatal conductivity, but had no effect on the relative chlorophyll content (SPAD values) or the potential and effective photochemical efficiency of photosystem II. However, intercellular CO2 concentrations and superoxide dismutase decreased in response to increasing Tl concentrations. Although 50 µg L-1 Tl significantly decreased the SPAD values, as well as the potential and effective photochemical efficiency of photosystem II, it had no effect on Pn or Tr. These results suggest that root restriction and oxidative stress are involved in the mechanism of Tl toxicity, but the photosynthetic system of A. donax was not harmed by certain concentrations of Tl, indicating the strong tolerance of this species to increased Tl pollution. [ABSTRACT FROM AUTHOR]