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 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 6 mM concentration CdSO₄ solution. Gas exchange parameters (photosynthetic rate (Pn), transpiration rate (Tn), intercellular CO₂ concentration (Ci) and water use efficiency (WUE)) were measured every day with portable photosynthesis system LI-6400. Content of photosynthetic pigments was 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 P. vulgaris plants decreased only by 4.3% and statistically insignificant, while Pn of V. fabo decreased by 35.9% (p < 0.05). Pn of P. vulgaris was decreasing till 3rd day after treatment, when it was 96% (p < 0.05) lower compared to reference treatment. On the contrary, the lowest Pn of Cd treated V. fabo plants was on the first day and it started to increase from the second day till the last one. WUE of Cd treated P. vulgaris was decreasing till the third day too and it improved a little on the last one, but still it was 54% (p < 0.05) lower compared to the re­ference. While WUE of V. fabo increased by 23% (p  <  0.05) and 16% (p  >  0.05) on the first and the last day after Cd treatment, respectively compared 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 P. vulgaris it decreased by 5.7% (p > 0.05), and for V. fabo – increased by 1.4% (p > 0.05) compared to the reference. Also decrease of dry biomass of P. vulgaris was greater than that of V. fabo