The Effect of Low Temperature and Low Illumination Intensity on the Photosynthetic Characteristics and Antioxidant Enzyme Activity in the Strawberry

Low temperature (LT) and low illumination (LI) are common meteorological factors posing a great risk to plants. This study aimed to clarify and quantify the effects of LT, LI, and their combined stress (LTLI) on the photosynthetic physiological processes of strawberry plants during the flowering stage. The results indicated that LI stress increased Chl<i>a</i> and <i>b</i> levels in strawberry plants while lowering the chlorophyll a/b ratio. In contrast, LT and LTLI stress reduced chlorophyll content. All stress conditions (LT, LI, and LTLI) decreased net photosynthetic rate, stomatal conductance, transpiration rate, the maximum photochemical efficiency of photosystem II, photosynthetic electron transport rate, and actual photochemical quantum efficiency. These stresses also raised intercellular carbon dioxide concentration, non-photochemical quenching coefficient, and levels of malondialdehyde, proline, hydrogen peroxide, and peroxide ion content. Moreover, LI stress treatment boosted the activity of superoxide dismutase, peroxidase, and catalase, while LT and LTLI stress initially raised the activity of these enzymes before it eventually declined. Importantly, the previously mentioned photosynthetic physiological parameters showed notable changes under the combined stress conditions. Ultimately, the TOPSIS model was used to quantitatively evaluate the impact levels of different stressors and treatment durations on the photosynthetic system of strawberry plants. In conclusion, the synergistic impact of LT and LI results in a reduction in photosynthetic rate and photosystem II activity, a disruption in the equilibrium of the antioxidant system, and an intensification of photoinhibition, ultimately leading to diminished photosynthetic efficiency in plants.