Leaf model showing the phenomenological energy fluxes per the excited cross sections (CS) of the leaves of the B. pendula growing on the reference site (T), post-coal mine heap (K), and post-smelter heap (P). Each relative value of the measured parameters is the mean (n = 10) and the width of each arrow corresponds to the intensity of the flux. Yellow arrow—ABS/CS, absorption flux per CS (approximated); green arrow—TR/CS, trapped energy flux per CS; red arrow—ET/CS, electron transport flux per CS; blue arrow—DI/CS, dissipated energy flux per CS; circles inscribed in squares—RC/CS, % of active/inactive reaction centres. White circles inscribed in squares represent reduced QA reaction centres (active), black circles represent non-reduced QA reaction centres (inactive); 100% of the active reaction centres responded with the highest mean value observed in the control conditions. Means followed by the same letter for each parameter in a row are not significantly different from each other according to the Tukey HSD test (p < 0.05). Letters are inscribed into arrows, except for RC/CS, where they are placed in a box in the bottom right corner of the square with circles. Abbreviations: T—reference population from Tychy; K—birch population from post-coal mine spoil heap; P—birch population from post-smelter spoil heap.