Effects of different light intensities on Strobilanthes cusia photosynthetic characteristics in Fujian Province

"Jian Indigo" made from stem and leave of Strobilanthes cusia is one of the genuine drugs in Fujian Province. S. cusia original plant occurs in dank conditions and grows in forests or generally shaded conditions. Although light intensity is the main cultivation factor of S. cusia, studies on the characteristics of S. cusia photosynthesis under different light intensities were limited. Hence studies on different light intensities (full sunlight, 30% sunlight and 6% sunlight) were carried out to investigate the effects of light intensity on photosynthetic characteristics of S. cusia in Fujian Province. Results showed that diurnal variations in photosynthetic rates under three treatments tracked di-peak curves. Among the three light intensity treatments, the rate of photosynthesis was highest in the 30% sunlight treatment. Compared with natural light (full sunlight), the 30% and 6% sunlight treatments had higher Fm, Fv/Fo, Fv/Fm, Yield, qP and lower qN. Under shaded conditions, photosynthetic rate of S. cusia increased with increasing chlorophyll a/b and photochemical activity in the light response centre, and decreasing light compensation point. Enhancing light energy conversion efficiency rate in photosynthetic system in compensation of insufficient light energy in low light intensity conditions also increased S. cusia photosynthetic rate. There existed a little correlation between photosynthetic rate and stomatal conductance in S. cusia, which suggested the non-stomatal factors were the main drivers of photosynthesis in shaded conditions. It was further noted that shading significantly increased the sensitivity of stomata to light intensity. While the effect of light intensity on leaf indigo content was not obvious, indirubin content under full sunlight was higher than under shaded conditions. The 30% sunlight treatment in intercropping conditions or under tree shades was most suitable for the growth and medicinal component accumulation of S. cusia in Fujian Province.