Photosynthetic performance and content of some nutrients in cadmium- and copper-treated barley plants

Barley (Hordeum vulgare L. cv. CE9704) plants grown in sand culture were exposed to increasing cadmium (Cd) (0, 14, 28, and 42 mg Cd kg(-1) sand) or copper (Cu) (0, 5, 10, and 15 mg Cu kg(-1) sand) concentrations for a duration of 10 days. The effect of excess Cd or Cu on plant growth, selected mineral elements content, leaf gas exchanges, and chlorophyll content were studied. The excess of Cd or Cu inhibited relative growth rate (RGR) of barley plants mainly through net assimilation rate (NAR) retardation, but leaf area ratio (LAR) was barely affected or unaffected. After 10 days of exposure, the shoot content of Cd and Cu was about 1/10 (Cu) to 1/20 (Cd) that of roots. Cadmium- and Cu-treated plants with equal RGR inhibition had some differences in photosynthesis response and in the content of some nutrients, which were not distinctive enough. Stomatal limitation to photosynthesis in Cd-treated plants was well expressed, but in Cu-treated plants factors limiting photosynthesis were more related with mesophyll constraints. Cadmium and Cu treatment reduced the chlorophyll content, relative to untreated plants more probably through degradation of photosynthetic components. In conclusion, among observed physiological disturbances in Cd and Cu-treated barley plants with relatively equal growth inhibition, the similarities prevailed over the differences.