Elevated CO2 enhances growth and differentially affects saponin content in Paris polyphylla var. yunnanensis

Paris polyphylla var. yunnanensis produces specific diosgenins and pennogenins of high medicinal value and is an increasingly important industrial biomedical resource. Attempts to meet the strong demand for its secondary metabolites are hampered by its slow growth rate, and in consequence natural populations are increasingly under threat, with increased yields required for large-scale cultivation. The response of P. polyphylla to artificial environmental conditions is therefore of considerable biological and industrial importance. In this study, we characterized the responses of two P. polyphylla cultivars to elevated CO2. The cultivar WY (western Yunnan), which originated from a cold, dry habitat, showed stronger photosynthetic activity and higher contents of bioactive compounds under ambient CO2 than the cultivar CY (central Yunnan), which is adapted to a warm, humid habitat. Cultivar WY showed higher photosynthetic activity and enhanced growth compared with CY under elevated CO2. Contents of the bioactive compound diosgenin of WY increased under elevated CO2 and thus total saponin content was maintained, consistent with the enhanced growth. The present results suggest that the responses of P. polyphylla cultivars to elevated CO2 may be due to the effects of their natural habitats. Photosynthesis, growth and diosgenin accumulation in WY are sensitive to elevated CO2, implying that WY is a potential candidate for industrial cultivation in a high-CO2 environment.