In order to explore the mitigatory mechanism of rare earths on the midday depression of photosynthesis, this study used fast-phase chlorophyll fluorescence technology combined with an antioxidant enzyme system to analyze the effects of lanthanum and cerium on the photosystem II (PSII) function of Pseudostellaria heterophylla leaves at noon. The results show that the maximum photochemical efficiency (F_v/F_m) and the photosynthetic performance index (PI_ABS) of P. heterophylla leaves during the photosynthetic noon-break are only 0.73 and 0.86, respectively. The leaves of P. heterophylla show obvious photoinhibition. The application of two rare earth fertilizers promotes the light energy absorption, capture, conversion, and electron transfer efficiencies of PSII in the P. heterophylla leaves and alleviates the photoinhibition caused by excess excitation energy. Additionally, the effect of lanthanum is better than that of cerium. In the fertilization groups, P. heterophylla leaves show higher PSII photochemical activity. Fertilization protects the oxygen-evolving complex (OEC) activity of P. heterophylla, thus reducing oxidative damage to the chloroplasts and preventing the dissociation of the thylakoids to maintain the normal physiological functioning of PSII, thereby reducing the degree of photoinhibition. Additionally, fertilization increases the electron transfer ability from Q_A to Q_B on the PSII electron receptor side of P. heterophylla. Correlation analysis shows that the fluorescence parameters V_L, V_K, and V_J are significantly negatively correlated with antioxidant enzyme activity and are significantly positively correlated with malondialdehyde content, relative electric conductivity and reactive oxygen species (ROS), which further indicates that rare earths can enhance the ROS scavenging system in plants and reduce the degree of membrane lipid peroxidation and plasma membrane damage, thereby maintaining the structure and function of the OEC on the donor side of PSII, increasing the electron receptor pool, and contributing to the defense against photoinhibition.

为探索稀土对光合作用午间抑制的缓解机制，本研究采用快相叶绿素荧光技术结合抗氧化酶系统，分析镧和铈对拟星藻光系统II（PSII）功能的影响。太子参在中午离开。结果表明，太子参叶片光合午休期间的最大光化学效率（ F _v / F _m）和光合性能指数（PI _ABS）分别仅为0.73和0.86。太子参的叶子表现出明显的光抑制。两种稀土肥料的施用促进了太子参叶中PSII的光能吸收、捕获、转换和电子转移效率，并减轻了由过量激发能量引起的光抑制。此外，镧的效果优于铈。在施肥组中，太子参叶片表现出较高的PSII光化学活性。施肥保护太子参的析氧复合物 (OEC) 活性，从而减少对叶绿体的氧化损伤并阻止类囊体的解离以维持PSII的正常生理功能，从而降低光抑制程度。此外，受精增加了太子参PSII 电子受体侧从Q _A到Q _B的电子转移能力。相关分析表明，荧光参数V _L、V _K和V _J与抗氧化酶活性呈显着负相关，与丙二醛含量、相对电导率和活性氧（ROS）呈显着正相关，进一步表明稀土可以增强植物体内的活性氧清除系统，降低膜脂过氧化程度和质膜损伤，从而维持PSII供体侧OEC的结构和功能，增加电子受体池，并有助于防御光抑制。