Effect of Technogenic Hydrocarbons on Chlorophyll a Variable Fluorescence Parameters in Leaves of Deciduous Plant Seedlings

The effects of technogenic hydrocarbons (benzo[α]pyrene, butyl acetate, and o-xylene) on the state of stress-sensitive photosystem II in leaves of seedlings of silver birch (Betula pendula Roth.), small-leaved linden (Tilia cordata Mill.), Norway maple (Acer platanoides L.), and little-leaf poplar (Populus pyramidalis Roz.) were assessed by pulse–amplitude-modulated (PAM) fluorimetry. The degree of response to intoxication was similar for toxins of different nature and depended on the previous stress in the plants, e.g., birch seedlings that had undergone natural stress reacted weaker to chemical stress. Poplar leaves showed the highest response to intoxication and rapid adaptability. The coefficient of nonphotochemical fluorescence quenching qN was the most sensitive parameter and increased after treatment with hydrocarbons by 2–5 times in seedlings of different species. Nonradiative dissipation of excitation energy was probably the main mechanism for protecting photosynthetic membranes under chemical stress.