Effects of greenhouse light intensity and quality on biomass and salidroside content in roots of Rhodiola sachalinensis

Rhodiola sachalinensis A. Bor, a perennial herb, belonging to the family Crassulaceae, is mainly distributed in mountains of 1700～2500 m above sea level. It is a very important medicinal plant with high activities of anti-fatigue, anti-senescence and anti-radiation, due to the secondary metabolite, salidroside in its roots. In order to investigate the effects of light intensity and light quality on plant growth and salidroside content in roots of Rh. sachalinensis, a controlled environmental study was conducted in a greenhouse in April 2000. Four light intensity levels (relative light intensities were 100%, 67.75%, 44.71% and 31.96% of full sunlight, respectively) were created by using neutral shading cloth, and four different light qualities were done by red, yellow, blue and green films (relative light intensities were 51.76%, 60.69%, 26.96% and 24.80% of full sunlight, respectively). On April 27, 3-year-old plants grown at a nursery in Daxinganling Mountain (124°02′E, 50°30′ N), were transplanted to pots (diameter 25 cm, depth 25 cm) in a greenhouse at Northeast Forestry University, Harbin, P. R. China (126°38′ E, 45°43′ N). Light controlled treatments were performed after 1 week of shoot development. Aboveground and root biomasses, the contents of chlorophyll a and chlorophyll b in leaves, and salidroside content in roots of Rh. sachalinensis were measured after 45 days of treatment, and whole plant biomass, root/shoot ratio, total chlorophyll content, chlorophyll a/b ratio and salidroside yield in roots (the product of salidroside content and root biomass) were calculated. Results revealed that the biomass of Rh. sachalinensis was affected by light intensity. The biomasses of the whole plant and roots tended to decrease as light intensity declined, though whole plant biomass was not influenced apparently when light intensity was 44.71% of full sunlight or higher. The biomasses of the whole plant were 87.82%, 84.95% and 37.46% with light intensities of 67.75%, 44.71% and 31.96% of full sunlight to the control of 100% full sunlight, and those of roots were 83.08%, 76.12% and 53.23%, respectively. Root/shoot ratio with light intensity of 31.96% of full sunlight was significantly larger than under other light intensity conditions. The contents of chlorophyll a, chlorophyll b and total chlorophyll in leaves of Rh. sachalinensis slightly decreased with the descent of light intensity. Shaded by red, yellow, blue and green films, whole plant and root biomasses were significantly less than that of the control without shading. To define the real effect induced by light quality, based on the effect of light intensity on biomass, the theoretical biomasses of the whole plant and for the control with the corresponding relative light intensities to that under different shading films were calculated. Thereby, whole plant biomasses under red, yellow, blue and green films would be 80.73%, 70.11%, 60.96% and 71.28% to the respective calculating values, and that of roots would be 90.24%, 76.80%, 52.83% or 52.00%, respectively. Thus, blue and green films would induce more root biomass loses of Rh. sachalinensis than would red and yellow films. Versus the control, root/shoot ratio was apparently enlarged under red, blue and green film treatments. Color film treatments positively affected on the contents of chlorophyll a, chlorophyll b and total chlorophyll, but only blue film caused a significant effect. When light intensities were 67.75% and 44.71% of full sunlight, though Rh. sachalinensis salidroside content lightly lowered to the control, salidroside yield was down significantly. Both the content and yield of salidroside in roots of Rh. sachalinensis under light of 31.96% of full sunlight declined remarkably to that under other conditions. Compared to the control, red film conducted an increase of 83% in salidroside content and of 35% in salidroside yield, whereas yellow, blue and green films did decreases of 56.95%, 72.22% and 31.94% in salidroside content and 70.43%, 92.35%, and 82.34% in salidroside y