Parameters of Miscanthus × giganteus photosystem under the influence of weather conditions

Purpose. To establish parameters of the photosynthetic system of Miscanthus × giganteus as affected by weather conditions during vegetation. Methods. Field studies were conducted at the Bila Tserkva Experimental Breeding Station of the Institute of Bioenergy Crops and Sugar Beet. The following chlorophyll fluorescence parameters were measured: Fo – minimum reliable fluorescence intensity at 40 μs, Fj – fluorescence intensity at the J-step (at 2 ms), Fi – fluorescence intensity at the I-step (at 30 ms), Fm – maximum fluorescence intensity at the P-step, Fv – maximum variable fluorescence, Fv/Fm – photochemical efficiency (quantum efficiency), Fv/Fo – efficiency of initial photosynthesis reactions, φPo – maximum quantum yield of primary photochemistry (at t = 0), VJ and VI – relative variable fluorescence at J-step and I-step, respectively, ψEo – efficiency/probability that an exciton, reducing QA to QA⁻, moves electrons further along the intersystem transport chain, ψRo – efficiency/probability of electron transfer from PSII to PSI acceptors, and δRo – efficiency/probability that electrons from intersystem carriers reduce the terminal electron acceptors on the PSI acceptor side. Results. In all years of research, miscanthus plants experienced stress caused by adverse weather conditions. In 2022, a significant moisture deficit was observed in the first half of vegetation when miscanthus was actively developing vegetative mass. In 2023, there were heavy rains at the beginning of vegetation, with a significant rise in average daily air temperatures by August. In 2024, high mean daily air temperatures started in April, then in June, drought occurred, and such conditions continued until the end of vegetation. Conclusions. An analysis of the basic parameters of the chlorophyll fluorescence induction curve – Fo, Fj, Fi, Fm, Fv, Fv/Fm, Fv/Fo, and φPo – revealed strong and very strong correlations with weather elements, demonstrating their suitability for assessing stress in miscanthus plants caused by adverse weather conditions during vegetation. However, in our study these indicators were not selective for discrimination between drought stress or heat stress, i.e. state of plant photosystems can be identified as stressed without determining the type of stress, particularly in case of combined stress. Further studies should aim to identify correlations between certain parameters of photosystem and certain stress factors.