The Effect of Light and Nitrogen Interaction on the Physiological Characteristics of Erythropalum scandens Bl.

Our study aims to investigate the photosynthetic and physiological responses of Erythropalum scandens Bl. seedlings to different light and nitrogen conditions is crucial for optimizing the cultivation process during the seedling stage. Two-year-old E. scandens cutting seedlings were used as materials, with four light levels L₀: 100% natural sunlight (NS), L₁: 70.85% NS, L₂: 52.45% NS, L₃: 13.85% NS and five nitrogen (urea, N: 46.67%) levels (N₀: 0 g/plant, N₁: 2.5 g/plant, N₂: 5.0 g/plant, N₃: 7.5 g/plant, N₄: 10.0 g/plant) being set. The photosynthetic and physiological characteristics of E. scandens seedlings under different light and nitrogen treatments were compared. The results showed that: (1) There were significant differences in various physiological indicators among different light and nitrogen treatments (P < 0.01), with light and nitrogen having significant main effects, and their interaction significantly affecting various physiological indicators (P < 0.01). (2) At the same nitrogen level, SS and SP content were highest under L₀ and L₁, decreasing gradually with decreasing light intensity, while MDA content was highest under L₀, with shading significantly reducing MDA content. POD was highest under L₂ treatment, and SOD activity showed a change of initially decreasing and then increasing, being higher under L₀ and L₃. Under the same light conditions, nitrogen at level N₂ significantly increased SS and SP content, MDA content under nitrogen application was higher than that without nitrogen application, and nitrogen application affected POD and SOD activity to varying degrees. (3) At the same nitrogen level, with increasing shading, P_n and T_r initially increased and then decreased, reaching peak values at L₁, total chlorophyll content showed a trend of initial increase and then decrease, while carotenoid content initially decreased and then increased, F_v/F_m and F_v/F₀ gradually increased. Under the same light conditions, high nitrogen (N₄) and no nitrogen application (N₀) were both unfavorable for increasing P_n, T_r, total chlorophyll content, F_v/F_m, and F_v/F₀ of E. scandens leaves, while carotenoid content showed different trends. (4) Subordinate function analysis results showed that physiological condition of L₀N₂ exhibited the highest quality, followed by L₁N₂.In general, insufficient light, nitrogen deficiency or excessive nitrogen application had detrimental effects on the photosynthetic capacity and physiological status of E. scandens seedlings. Adequate light and appropriate nitrogen fertilizer management were more favorable for enhancing the photosynthetic capacity and physiological status of E. scandens seedlings.