Abstract: In the context of global climate warming, Korean pine (Pinus koraiensis) seedlings with advanced growth are highly susceptible to low temperature in spring, which in turn, affecting regeneration. To explore the impacts of extremely low temperatures in spring on the early growth of Korean pine seedlings, we conducted a manipulative experiment to investigate the combined effects of spring low temperature (T1: 10 ℃, T2: 6 ℃, T3: 2 ℃, T4: -2 ℃, T5: -6 ℃) and different light intensities (L1: 150 μmol·m^-2·s^-1; L2: 750 μmol·m^-2·s^-1; L3: 1500 μmol·m^-2·s^-1) on photosynthetic and fluorescence characteristics of one-year-old Korean pine seedlings. The results showed that: (1) With decreasing temperature, photosynthetic variables tended to decrease. At 6 ℃ and 10 ℃, photosynthetic capacity (net photosynthetic rate (P_n), stomatal conductance (G_s), intercellular CO₂ concentration (C_i), transpiration rate (T_r)) was highest in moderate light intensity (750 μmol·m^-2·s^-1), and all of which were higher than under low light intensity (150 μmol·m^-2·s^-1) and high light intensity (1500 μmol·m^-2·s^-1) treatments. (2) F_v/F_m, Φ_PSⅡ, qP and ETR significantly decreased with decreasing stressed temperatures, while F_o and NPQ gradually increased. The PSII photosynthetic system suffered the least damage at light intensity of 750 μmol·m^-2·s^-1, while light intensity (L3) under low-temperature stress (<2 ℃) caused the most extensive damage to PSII photosynthetic system. (3) Under low temperature stress, both low and high light intensity environments exacerbated the damage to the photosynthetic system. Both stomatal and non-stomatal limiting factors contributed to the decline in P_n, with most severe damage under high light conditions. Based on these results, we proposed management measures, such as shading and insulation, establishment of mixed forests of coniferous and broad-leaved tree species, and thinning, to avoid the impacts of low temperatures, aiming to provide scientific basis for the early growth and regeneration of Korean pine seedlings.

Key words: Pinus koraiensis seedling, low temperature stress, light intensity, photosynthetic characteristics, chlorophyll fluorescence parameter