The impact of low concentration of cadmium on the photosynthetic gas exchange and growth of pea and barley plants

Abstract

Photosynthetic gas exchange and growth characteristics were investigated in pea and barley plants using 1 mM Cd treatment. Plants were sown in a neutral peat substrate and at leaf development stage were treated with 1 mM cadmium concentration solution. Gas exchange parameters (photosynthetic rate, Pn; intercellular CO2 concentration, Ci; transpiration rate, Tn; water use efficiency, WUE) were measured with portable photosynthesis system LI-6400 on the fifth day after Cd treatment. Under Cd stress photosynthetic rate of pea and barley plants decreased by 16.7 % (p < 0.05) and 12.8 % (p < 0.05) respectively, compare to the reference treatments. The photosynthetic response of pea leaves to cadmium stress was slightly different from barley ones. Intercellular CO2 concentration decreased by 27.4 % (p < 0.05) in pea leaves but it increased by 33.5 % (p < 0.05) in barley ones. Cadmium treatment had no statistical significant effect on transpiration rate of pea plants, while transpiration rate of Cd treated barley decreased by 23.1 % (p < 0.05), compare to the reference treatment. The high increase of Ci of barley plants suggests that enzymatic dark reaction of photosynthesis was strongly affected, but the parallel change of photosynthetic and transpiration rates of barley showed that the photosynthetic response to Cd stress could be also attributed to the alteration of the photosystem and transpiration rate. CO2 reduction processes of Cd treated pea leaves increased (because Ci decreased), but this had no positive effect on photosynthetic rate, and the photosynthetic rate of pea decreased by 4 % more than photosynthetic rate of barley ones. Whereas cadmium stress produced disturbances in water balance of pea and thus reduction in water use efficiency by 26.5 % (p < 0.05) arose. The changes of dry biomass of cadmium treated plants were weak and statistical insignificant