Abstract
Oxathiapiprolin is the first member of the piperidinyl thiazole isoxazoline fungicides developed globally as DuPont™ Zorvec™ for the control of plant diseases caused by Oomycete pathogens. Although they have great application potential, ecotoxicological data, especially their non-target effects on photosynthesis of algae and higher plants are completely lacking. Effects of a novel oxathiapiprolin biocide on the photosynthesis of Chlorella pyrenoidosa were therefore investigated using chlorophyll a fluorescence and thermoluminescence techniques. Effects of the bioicide on photosynthetic electron transport and energy absorption and dissipation were concentration dependent. Inhibition of the electron donor side of PSII significantly increased as oxathiapiprolin concentration increased from 0 to 100 μM. The oxathiapiprolin treatment increased the effective antenna size per reaction center and the dissipated energy flux per reaction center. It damaged PSII reaction centers and blocked the electron transport flux, thus inhibiting photochemical activity in Chlorella pyrenoidosa. Exposure to oxathiapiprolin at concentrations up to 50 μM had little effect on QA− reoxidation kinetics on the electron acceptor side. Only a higher concentration (100 μM) of the oxathiapiprolin biocide exerted obvious inhibitory effects on QA− reoxidation. At 100 μM, electron transport beyond QA was drastically blocked, and more QA was reoxidized through S2(QAQB)− charge combination. As the concentration increased from 0 to 100 μM, the thermoluminescence C band decreased with increasing oxathiapiprolin concentration, whereas the intensity of the Q band increased which was associated with the decrease of B1 and B2 band intensity. This confirmed that the bioicide hindered electron transfer after QA and caused an increase of S2/S3QB− and TyrD+ QA− recombination. This study implies that when oxathiapiprolin biocides are applied to farmlands, they may pose a potential risk to algae and higher plants.
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