ABSTRACT
Results and Discussion e photosynthetic response curve (PRC) of the control was characterised by an increase in oxygen evolution according to the increase in PFD up to 612 µmol m-2 s-1 (the highest PFD-value used in the experiments) and a decrease in oxygen evolution due to the inhibition of photosynthesis when PFD became constant (612 µmol m-2 s-1, Fig. 1a). A peak of higher respiration immediately after the cessation of illumination can be explained by the light-enhanced dark respiration (LEDR, the rate of change of oxygen consumption - an acceleration), which contributed to the basal dark respiration. e behaviour of PRC is important evidence of how favourable the conditions are for photosynthesis [14]. e type of PRC described above was found in similar investigations to be typical in the green agellate Euglena gracilis [15]. Similarly, this type of PRC can be considered as common in C. reinhardtii, too. At all treatments this basic type of PRC was observed. e stepwise drop in oxygen evolution at the maximum irradiance value in g. 3a,b and g. 5a,b should be considered as an artefact specic to the Light Pipette model used (when the value of oxygen saturation in the cuvette exceeds 200 %, unpublished results of a methodical study). Increasing concentrations of copper led to decrease in maximum values of oxygen evolution compared to the control, demonstrating especially severe impacts at the concentrations of 0.5 mg l-1 and higher (Fig. 1b,c,d,e,f ). e treatments with nickel, lead or zinc did not caused such strong inhibitory eects as in the case of copper. Moreover, in the case of nickel (Fig. 2) maximum values of oxygen evolution were higher than those in the control and no inhibition of photosynthesis was observed when the PFD became constant (612 µmol m-2 s-1). Increasing concentrations of nickel seemed to be stimulative based on the shape of PRCs. Only slight inhibition of photosynthesis at the constant maximal PFD values was detected in the cases of lead or zinc treatments (Figs. 3, 4, respectively) and maximum values of oxygen evolution were equal to or higher than in the control. e treatment with pentachlorophenol led to prolongated compensation points at lower concentrations (0.1 and 0.5 mg l-1) and to severe impacts on photosynthesis at concentrations of 1.0 mg l-1 and higher (Fig. 5) comparable to those caused by copper treatments.
