Light intensity effects on leaf chlorophyll fluorescence and thermoluminescence in perennial ryegrass

With the expeditious development of optoelectronics, the light-emitting diode (LED) technology as supplementary light has shown great effects to landscape plants. In urban areas, artificial lighting alters natural light conditions, potentially affecting plant performance. In current study, the six light intensities (100–600 µmol/(m2·s)) and their effects on growth attributes, indices of chlorophyll fluorescence (CF) and thermoluminescence (TL) in seedlings of perennial ryegrass (Lolium perenne L.) was investigated. Results showed that moderate light intensity (300–400 µmol/(m2·s)) enhanced germination, biomass accumulation, chlorophyll content, and photosynthetic efficiency, while higher and lower intensities (100 and 600 µmol/(m2·s)) induced oxidative stress, reduced photosynthetic activity, and altered electron transport in photosystem II (PSII). CF analysis revealed impaired photochemical efficiency under higher and lower light, supported by decreased Fv/Fm and performance index (PIABS). TL measurements indicated disruptions in PSII charge recombination under stress, with the disappearance of the B band and emergence of the afterglow (AG) band. These findings suggested that perennial ryegrass showed the highest performance under moderate light but exhibited indicators of photoinhibition and oxidative stress under extreme intensities, highlighting the need for optimized artificial lighting in urban green spaces.