[Seasonal variations in biomass and salidroside content in roots of Rhodiola sachalinensis as affected by gauze and red film shading].

Rhodiola sachalinensis A. Bor, a perennial herb, belonging to the family Crassulaceae, is mainly distributed in mountains at the altitudes of 1,700-2,500 m. It is a typical alpine plant and a very important medicinal plant with high activities of anti-fatigue, anti-senescence, and anti-radiation, due to the secondary metabolite salidroside in its root. Our previous findings have proven that red light promotes salidroside synthesis remarkably but decreases biomass insignificantly, resulting in a higher yield of salidroside in roots of Rh. sachalinensis in a greenhouse. In order to investigate the influences of shading and red light on seasonal variations in biomass and salidroside content in Rh. sachalinensis roots, the effects on 3 or 4 years old Rh. sachalinensis plants in a nursery in Daxinganling Mountain (124 degrees 02' E, 50 degrees 30' N) were studied in 2001. Compared to the control (CK) of full sunlight, 6 treatments with neutral transparent film and gauze, or red film alone had been conducted for 131 days. In treatment I, Rh. sachalinensis was shaded with neutral transparent film and gauze to achieve an irradiance 51.8% of full sunlight. In treatment II, the plants were shaded by red film alone, but the irradiance was as that in treatment I. In treatments III, IV, V and VI, neutral transparent film and gauze were originally used on May 8, then shifted to red film on Jun 3, July 4, August 4 and September 2, respectively and all experiments stopped on September 16, 2001. Rh. sachalinensis roots were harvested on 2-4th from June to September and finally on September 16, and root-biomass and salidroside content were measured. Root-biomass in plants decreased significantly under shading with neutral transparent film and gauze compared to the control with full sunlight, but little variations in salidroside content and yield. In comparison with shading by neutral transparent film and gauze, root-biomass reduced lightly and salidroside content and yield in roots were increased remarkably under red-film shading. At the end of the season, salidroside content under red light was 163% in 3-year-old and 155% in 4-year-old Rh. sachalinensis roots; whereas salidroside yields were 144% in 3-year-old and 145% in 4-year-old Rh. sachalinensis roots to those in plants under shading. The results also showed that the enhancement in the salidroside content and yield were little related to the duration of red film shading, which implied that in order to increase salidroside content and get higher salidroside yield, but less affect root-biomass, Rh. sachalinensis may be shaded with red film just several days before harvest.