Effects of light quality and photoperiod on the growth and physiology of Paramichelia baillonii seedlings

Abstract: In order to explore an efficient artificial light environment for improving the quality of Paramichelia baillonii and shortening its cultivation cycle, the annual seedlings of P. baillonii were exposed to five composite lights, red+ blue (8R1B, 6R1B), red+blue+purple+green (8R1B1P1G, 6R1B1P1G), and white light (W) with two photoperiods (12 h穌-1,16 h穌-1), Two-factor experiment with randomized block design and subordinate function were uesd to explore the response pattern of the growth, photosynthetic pigments and endogenous hormones of P. baillonii seedlings to different light qualities and photoperiods. The results were as follows: (1) Light quality, photoperiod, and their interaction had significant effects on height growth, leaf area, chlorophyll a, zeatin (ZR), abscisic acid (ABA) content, endogenous hormone ratio (IAA/ABA, (IAA+GA3+ZR)/ABA), etc. (P<0.05) (2) 16 h穌-1 photoperiod was conducive to the improvement of height growth, leaf area, seedling quality index, biomass, chlorophyll a, auxin (IAA), ZR content, and endogenous hormones ratio. (3) Under 16 h穌-1, height growth, leaf area, and seedling quality index under 8R1B treatment reached the maximum value, which were 21.84 cm, 158.39 cm2 and 2.43 respectively; Compared with the 6R1B treatment, the 8R1B had higher chlorophyll a/b and ZR content; Compared with the 6R1B1P1G treatment, the 8R1B1P1G had higher chlorophyll a, a/b, carotenoids, IAA, gibberellin (GA3) and endogenous hormones ratio. In conclusion, Red-blue composite light quality with higher red ratio and proper extension of photoperiod are conducive to improving the quelity of P. baillonii, and the addition of purple-green light cannot promote its growth, 16�8R1B is the most suitable light condition for the growth of P. baillonii seedlings.