The dynamics of photosynthetic parameters of Phaseolus vulgaris and Vicia fabo under strong cadmium stress

Abstract

One of the most toxic metals is cadmium, which inputs include those from commercial fertilizers, sewage sludge and other wastes used as soil amendments and also atmospheric deposition. The aim of this experiment was to study the dynamics of the photosynthetic parameters of bean (Phaseolus vulgaris L.) and broad bean (Vicia fabo L.) under strong cadmium stress effect. Plants were sown in a neutral (pH 6.0–6.5) peat substrate, when 2nd true leaf unfolded, growth substrate was watered with 6mM concentration CdSO4 solution. Gas exchange parameters (photosynthetic rate (Pn), transpiration rate (Tn), intercellular CO2 concentration (Ci) and water use efficiency (WUE)) were measured on every day with portable photosynthesis system LI-6400. Content of photosynthetic pigments were analyzed in acetone extract using a spectrophotometer on the last 5th day of the experiment. On the first day of treatment the Pn of Cd treated Phaseolus vulgaris plants decreased only by 4.3% and statistically insignificant, while Pn of Vicia fabo decreased by 35.9% (p<0.05). Pn of Phaseolus vulgaris was decreasing till 3rd day after treatment, when it was 96% (p<0.05) lower, compare to reference treatment. On the contrary the lowest Pn of Cd treated Vicia fabo plants were on the first day and it started to increase from the second day till the last one. WUE of Cd treated Phaseolus vulgaris was decreasing till third day too and it improved a little on the last one, but still it was 54% (p<0.05) lower, compare to the reference. While WUE of Vicia fabo increased by 23% (p<0.05) and 16% (p>0.05) on the first and the last day after Cd treatment respectively, compare to the reference. The changes, detected on the last day of the experiment, of chorophyll a and b ratio were different too, i. e. for Phaseolus vulgaris it decreased by 5.7% (p>0.05), and for Vicia fabo – increased by 1.4% (p>0.05), compare to the reference. [...]