The effect of cadmium and lead pollution on growth and physiological parameters of field beans (Vicia faba)
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Research on the impact of soil contamination on crops is important as plants directly take up heavy metals from the soil through the roots, so heavy metals can enter the food chain. The aim of this study was to investigate the impact of cadmium (Cd) and lead (Pb) pollution on growth and physiological parameters of field beans. Plants in the vegetation experiment were grown under controlled conditions. Changes in growth and physiological parameters were studied at five levels of Cd (0–25 mg L -1 ) and at 6 levels of Pb in substrate: from (0–1,000 mg L -1 ) at the first day of the experiment, to (0–2,000 mg L -1 ) at the end of the experiment after gradual Pb additions after every sample collecting day. Methods used for analysing the plant material: the content of amino acid proline and photosynthetic pigments were determined by spectrophotometry; chlorophyll a fluorescence parameters – using continuous excitation chlorophyll fluorimeter. The fresh weight of plant above-ground parts and roots was detected. The growth and development of field beans was slightly influenced by increasing amount of Cd and Pb in substrate only at the end of the experiment. The highest Cd treatments (Cd20 and Cd25) caused 2.5 and 1.3 times increased proline concentration in bean leaves. The chlorophyll a + b content and chlorophyll a fluorescence parameter Fv/Fm changed differently throughout the experiment. In general, during the experiment, there was a tendency for the content of proline in leaves for Pb treatments to be increased compared to control. At the end of the experiment the content of proline in field bean leaves of the highest Pb treatments (Pb600 + 100 + 400 + 500, Pb800 + 100 + 400 + 500 and Pb 1,000 + 100 + 400 + 500) was 1.66, 1.44 and 1.55 times higher, respectively, than that of the control plant leaves. The negative impact of exposure to Pb on chlorophyll a + b, chlorophyll a fluorescence parameter PIndex and Fv/Fm in bean leaves was less pronounced compared to Cd. The obtained results confirm that field beans until their flowering stage can grow and develop in the presence of a large amount of Cd and Pb in substrate without significant growth inhibition and detrimental impact on physiological parameters, if optimal cultivation conditions are provided.