Drought stress-induced changes in PSII functioning in ecologically contrasting plants: chlorophyll fluorescence study of poikilohydric and homoiohydric species

Dehydration reduces photosynthetic performance in leaves and other photosynthetic organs in response to drought. This decline is linked to changes in chlorophyll fluorescence, which reflects reduced photosystem II activity and increased protective non-photochemical quenching (NPQ). This study examined NPQ dynamics during desiccation across diverse species, including lichens, mosses, conifers, crops, and C₃ and C₄ plants, using the method of NPQ induction and relaxation curves. Gradual dehydration from a full-hydration state (RWC 100%) to complete dryness (RWC 0%) was applied in order to compare poikilohydric and homoiohydric species. NPQmax (light period), NPQrelax (dark period end), and the initial slopes of NPQ rise (α) and decline (β) were evaluated. Relative electron transport rate curves were also assessed. Results showed the above NPQ parameters are highly sensitive to dehydration, suggesting their usefulness - along with standard maximum (FV/FM) and effective quantum yield (ΦPSII) - as early indicators of drought stress in PSII across plant groups.