Physiological characteristics, dry matter, and active component accumulation patterns of Changium smyrnioides in response to a light intensity gradient

Context: Changium smyrnioides Wolff (Apiaceae) is an endangered medicinal plant with numerous pharmacological uses. Objective: To investigate the effect of light intensity levels on the growth and accumulation of secondary metabolites of C. smyrnioides, cultivated seedlings were subjected to different relative light intensities via sun-shading. Materials and methods: Changium smyrnioides seedlings were subjected to five irradiance treatments (100, 60.54, 44.84, 31.39, and 10.56% sunlight) in glasshouse for 9 months. Enzymatic and non-enzymatic antioxidants with spectrophotometric method, photosynthetic parameters with Li-6400XT, dry matter accumulation and active component contents in the root with spectrophotometric and HPLC method were analyzed. Results: With an increase in relative light intensity levels, activities of enzymatic and non-enzymatic antioxidants, and malondialdehyde (MDA) contents were increased overall, while net photosynthetic rate (Pn) and dry matter accumulation patter first increased and then declined. The highest net photosynthetic rate (30.68 μmol/m2·s) and dry root weight (5.07 g) were achieved under 60.54% sunlight. Lower relative light intensity levels stimulated the accumulation levels of bioactive compounds in the roots so that the highest contents of mannitol (1.35%) and choline (405.58 μg/g) were recorded under 31.39% sunlight, and the highest polysaccharide content (10.80%) were achieved under 44.84% sunlight. With a decrease in the relative light intensity levels, the water-soluble component content increased first and then decreased. Discussion and conclusion: The results revealed that 31.39–60.54% sunlight serve as appropriate relative light intensity conditions for cultivated C. smyrnioides.