Near-infrared radiation modulates photosynthetic performance and antioxidant defence mechanisms in Azolla pinnata L

Light quality directly influences the growth and development of plants. Different wavelengths of photosynthetically active radiation (PAR) show differential responses at molecular, biochemical and physiological levels in plants. The impact of light, beyond the PAR range (> 700 nm) is poorly understood on plants. In the present investigation, we evaluate the effects of near-infrared irradiation (NIR-700-1100 nm) on the aquatic plant Azolla pinnata L., focusing on oxidative stress, antioxidant defence, and photosystem II (PSII) performance. Plants were exposed at two distances (1 ft, NIR₁; 2 ft, NIR₂), and Chlorophyll a fluorescence (ChlF) transients were analyzed using the JIP-test. NIR₁ elicited pronounced oxidative stress, with elevated malondialdehyde (MDA), proline accumulation, and partial inhibition of superoxide dismutase (SOD), catalase (CAT), and guaiacol peroxidase (GPOD) activities, accompanied by declines in F_v/F₀, the maximum quantum yield of photosynthesis (φPo), the quantum yield of electron transport (φEo), reaction centre per cross section (RC/CS), and performance indices (PIs), and increased energy dissipation (φDo), indicating photoinhibition. In contrast, NIR₂ induced moderate stress, improving photochemical efficiency, maintaining reactive oxygen species (ROS) homeostasis, and partially acclimating the photosynthetic apparatus. These results demonstrate that NIR exerts significant modulatory effects on plant physiology and biochemistry.