Abstract: To study the mechanism of photosynthetic attenuation in cucumber seedling leaves under low temperature and weak light conditions, using cucumber variety 'Jinyou 101' as experimental material, a two-factor environmental control experiment of low temperature and weak light was carried out by using artificial climate boxes in Nanjing University of Information Science and Technology from 2020 to 2021. The daytime/night temperature was set at 13℃/3℃, 16℃/6℃, 19℃/9℃ and 12℃/22℃, and the photosynthetically active radiation (PAR) was set at 200, 400μmol·m−2·s−1. There were eight treatments, each of which lasted for 3, 6, 9 and 12 days, respectively. The treatment with light and temperature of 28℃/18℃ and 800μmol·m−2·s−1 was used as control (CK). The chloroplast pigment content, photosynthetic parameters, and kinetic parameters of rapid chlorophyll fluorescence induction in cucumber leaves at the seedling stage were measured under different treatments. The results showed that: (1) the chloroplast pigment content of cucumber leaves decreased with the decrease of temperature and PAR, and decreased with the prolongation of treatment time. (2) Under different treatments, the maximum photosynthetic rate (Pmax), light saturation point (LSP), stomatal conductance (Gs), and transpiration rate (Tr) decreased with the increase of stress degree and time, and the light compensation point (LCP) increased with the increase of stress degree and time. The results showed that the deeper the degree of low temperature and weak light stress and the longer the stress time, the weaker the photosynthesis of cucumber leaves. (3) With the deepening of stress and the prolongation of stress time, the JIP phase of the fast fluorescence induction kinetic curve (OJIP curve) of cucumber leaves decreased gradually, the parameters of energy distribution ratio (φPo, ψEo, and φEo) decreased gradually, and the light energy absorbed (ABS/RC) and trapped (TRo/RC) per unit active reaction center gradually increased, but the light energy used for electron transport (ETo/RC) still decreased. This study confirmed that low temperature and weak light treatment reduced the stomatal conductance of cucumber leaves and hindered gas exchange; the antenna pigment content decreased, and the light energy absorbed and captured by the leaves decreased; the performance of PSII decreased, and the energy used for photochemical reactions decreased; therefore, the photosynthesis of the leaves decreased.

Key words: Cucumber, Low temperature and weak light, Photosynthesis, Rapid fluorescence, OJIP curve