PARAMETERS OF CHLOROPHYLL FLUORESCENCE INDUCTION CURVES TO STUDY WHITE SEA PHYTOPLANKTON AND ITS SENSITIVITY TO H2S

Abstract

The activity of natural phytoplankton in the presence of adverse factors is actively studied using chlorophyll fluorescence. The effect of H₂S at different concentrations on the light-induced photo-synthesis of natural cryptophyte microalgae Rhodomonas sp. (meromictic waters of the White Sea) was studied using chlorophyll fluorescence induction curves. Fluorescence induction curves (OJIP curves) were recorded using an Aquapen–C 100 fluorometer (Photon System Instruments, Brno, Czech Republic). It was shown that exposure to H2S (8 mg/L) decreased the relative maximum electron transport rate (ETR_max) and the maximum light energy utilization coefficient (α), while non-photochemical fluorescence quenching), associated with a relative increase in the dissipation of excess energy, increased. Analysis of fluorescence induction curves revealed that incubation of microalgae for 10 min with H₂S at concentrations above 2.3 mg/L significantly reduced the functional activity of PSII (PI_ABS), expressed as high values of the quantum yield of PSII photochemistry (F_V/F_M), the proportion of active reaction centers (ABS/RC), and the quantum yield of electron transport in PSII (φE₀). A decrease in electron transport is accompanied by an increase in the dissipation of unused light energy (DI₀/RC). H₂S at concentrations above 2.3 mg/L reduced the amplitude of all phases, primarily shortening the I-P phase, indicating disruption of electron transport in the plastoquinone-cytochrome b₆f complex between photosystems. Thus, natural Rhodomonas sp. microalgae experience stress when exposed to 2.3 mg/L H₂S, which is significantly higher than the concentrations typical for the chemocline and anaerobic zones of water bodies where Rhodomonas sp. are found. The use of fluorescence methods is proposed for studying the state of phytoplankton in coastal meromictic water bodies with varying H2S concentrations.