Effects of Blue Film on Photosynthetic Parameters and Seedling Growth of Populus schneideri Seedlings

Purpose To elucidate the effect of light quality components on the growth of Populus schneideri seedlings under blue film.

Methods The annual cuttings of P. schneideri seedlings were selected and cultured under arched greenhouses made of blue and white films for 60 days; and their growth indexes, leaf anatomical structure, photosynthetic parameters, photosynthetic pigment and sugar contents were determined.

Results The blue film was able to promote the seedling height growth and the increase of leaf length and width of P. schneideri seedlings, and its seedling height, leaf length and leaf width were 36.36%, 418.52% and 495.24% higher than those of white film, which made them extremely significantly different. Compared with the white film, under the blue film treatment, the thickness of upper epidermis of leaves was significantly thinner, whereas the thickness of leaf, palisade tissue, spongy tissue, and lower epidermis were only slightly increased. The photosynthetic gas exchange parameters transpiration rate (T_r), net photosynthetic rate (P_n), intercellular CO₂ concentration (C_i), and stomatal conductance (G_s) significantly or extremely significantly increased under blue film treatment, indicating that the blue film treatment was able to improve the photosynthetic efficiency of P. schneideri seedlings. Under the blue film treatment, the apparent quantum efficiency, the maximum net photosynthetic rate, the carboxylation rate, and the leaf photorespiration rate were extremely significantly higher than those under the white film, while the CO₂ saturation point and the CO₂ compensation point were significantly or extremely significantly smaller than those under the white film, indicating that the blue film treatment made P. schneideri seedlings better adapted to low light, but weaker adapted to high CO₂ concentration. Under the blue film treatment, the contents of chlorophyll a, chlorophyll b, starch, and reducing sugar contents were 22.69%, 41.18%, 65.85%, and 54.26% higher than under the white film, respectively, whereas sucrose content was significantly lower compared to the white film.

Conclusion P. schneideri seedlings strongly adapt to a high proportion of blue light, and the blue film can promote the seedling height growth of P. schneideri seedlings and the photosynthesis of the plants by increasing the leaf G_s, chlorophyll content, and the activity and content of RubisCO. The results provide a research basis for analyzing the mechanism of P. schneideri adapting to a high proportion of short-wave light, as well as a scientific basis for selecting and optimizing the light quality conditions for the introduction and cultivation of P. schneideri.