Abstract: The tomato variety "Fenguan" was used in a control experiment in a Nanjing University of Information Science and Technology experimental greenhouse from December 2019 to April 2020. Continuous light supplementation for 300min was used as the control treatment (CK). Treatment 1 (L1) was supplemented with light twice a day for 150min each time at an interval of 120min. Treatment 2 (L2) was supplemented with light 3 times a day for 100min each time and 2 times at 60min intervals. Treatment 3 (L3) was supplemented with light 4 times a day for 75min each time and 3 times at 40min intervals. Treatment 4 (L2) was supplemented with light 5 times a day for 60min each time and 4 times at 30min intervals. Photosynthetically active radiation was 600μmol·m⁻²·s⁻¹. The chlorophyll content, photosynthetic parameters, kinetic parameters of rapid fluorescence induction, and spectral characteristics of tomato seedling leaves were measured under supplementary light at different intervals. The results showed that (1) the increase in the frequency of light supplementation interval could promote the synthesis of some pigments in the leaves of tomato seedlings. At 36 days of treatment, chlorophyll-a content was 16.3% higher and carotenoid content was 19.6% more in the L4 treatment than in CK. (2) The three red-edge parameters λred, Sred, and Dred of tomato leaves under intermittent light supplementation showed a typical "redshift" phenomenon with increasing interval frequency, but the chlorophyll changes of leaves differed from the spectral pattern at the early stage of light supplementation. (3) The light saturation point (LSP), apparent quantum efficiency (AQE), and light compensation point (LCP) of tomato seedling leaves under prolonged intermittent light supplementation were higher than those of the continuous light treatment, and the higher interval frequency, the higher the net photosynthetic rate and the greater the photosynthetic capacity. However, tomato leaf stomata exert a delayed effect on light fluctuations, and stomatal delay alters the light capture process of leaf photosynthesis while limiting the transpiration and carbon exchange processes of stomatal movement. (4) The effect of intermittent light supplementation on the energy partitioning of PSII reaction centers showed a short-term reduction in the maximum photochemical efficiency of leaves, with an increase in the quantum yield captured by the reaction center (φPo) and for electron transfer (φEo) and a decrease in the quantum ratio for heat dissipation (φRo) when the number of treatment days increased, with a greater change at L4, where φPo decreased at L4 compared to CK at treatment day decreased by 3.8% at day 9 and increased by 11.6% at day 36, and φRo increased by 4.8% at L4 treatment and decreased by 6.9% at day 36 compared to CK at day 9 of the treatment.

Key words: Tomato seedlings, Intermittent supplemental light, Interval frequency, Chlorophyll content, Photosynthetic characteristics