Growth, physiological, and photosynthetic responses of Cyclobalanopsis glauca seedlings to light variation and phosphorus-potassium addition

To investigate the growth, physiological and photosynthetic responses of Cyclobalanopsis glauca seedlings to light variation and phosphorus-potassium addition, aiming to screen treatment groups suitable for regulating Cyclobalanopsis glauca seedlings under different phosphorus-potassium nutrient and light conditions, and to provide scientific basis for the cultivation of high-quality seedlings of Cyclobalanopsis glauca.

A three-factor pot experiment was conducted using one-year-old Cyclobalanopsis glauca seedlings as the research subjects, with 2 light levels (55% natural light, full light), 4 phosphorus levels (0, 2.4, 4.8, 7.2 g/plant), and 3 potassium levels (0, 1.6, 3.2 g/plant). The growth (seedling height, root collar diameter, root biomass, stem biomass, leaf biomass, and total biomass), physiological indicators: catalase activity (CAT), peroxidase activity (POD), soluble sugar content (SS), soluble protein content (SP), and malondialdehyde content (MDA), and photosynthetic gas exchange parameters Net photosynthetic rate (P_n), Stomatal conductance (G_s), and Intercellular CO₂ concentration (C_i) of the seedlings under each treatment were measured. The best treatment combination was selected through a comprehensive analysis of three-factor variance, correlation analysis, seedling quality index evaluation, and fuzzy function analysis.

Under appropriate phosphorus and potassium addition, the full light treatment significantly increased root collar diameter, root biomass, stem biomass, leaf biomass, total biomass, peroxidase activity, catalase activity, soluble sugar content, soluble protein content, G_s, and C_i compared to the shading treatment. Among different phosphorus content levels, seedling height, root collar diameter, root biomass, stem biomass, leaf biomass, total biomass, catalase activity, peroxidase activity, soluble sugar content, P_n, and G_s showed a trend of first increasing and then decreasing with the increase in phosphorus content, with the maximum values typically occurring at the P2 (2.4 g/plant) and P3 (4.8 g/plant) levels. The SP content decreased first and then increased with increasing phosphorus content, while MDA content decreased. Among different potassium content t, seedling height, root biomass, stem biomass, leaf biomass, total biomass, SS content, P_n, and G_s showed a trend of first increasing and then decreasing with increasing potassium content, with the maximum values typically occurring at the K2 (1.6 g/plant) level, while POD activity, CAT activity, and SP content showed a trend of first decreasing and then increasing.

Through comprehensive analysis, the LP2K2 (full light, phosphorus 2.4 g/plant, potassium 1.6 g/plant) treatment group exhibited the best performance in terms of growth, photosynthetic efficiency, antioxidant enzyme activity, and other indicators for Cyclobalanopsis glauca seedlings.