Impact of phosphorus and potassium fertilizers on growth and anthraquinone content in Rheum tanguticum Maxim. ex Balf

Abstract The dried root of Rheum tanguticum plays an important role in formulations and prescriptions in traditional Chinese medicine and Kampo medicine. Due to over-exploitation, R. tanguticum resources have decreased sharply in recent years. The main objective of our investigation (a 3-year field experiment) was to explore the effect of different levels of phosphorus (superphosphate) and potassium (potassium sulfate) fertilizer on the biomass (root fresh weight, root increment, and root dry weight), yield, dry matter content, and anthraquinone content of this plant at different harvesting stages (green stage, growth stage, and wilting stage) under alpine conditions. The root fresh weight and root dry weight increased significantly at the wilting stage following treatment with 90 kg P 2 O 5 /ha (100% and 59%, respectively) in 2016 and 75 kg K 2 O/ha (43% and 41%, respectively) in 2015 compared to the control. The yield of root dry weight obtained from three-year-old R. tanguticum plants was 9200 kg/ha when 90 kg P 2 O 5 /ha of phosphorus fertilizer was applied, and 10,400 kg/ha when 75 kg K 2 O/ha of potassium fertilizer was applied. This yield reached a maximum at the wilting stage. The anthraquinone content of two-year-old R. tanguticum plants had already reached the standard level of the Chinese Pharmacopoeia ; however, three-year-old plants had double the anthraquinone content of two-year-old plants. Phosphorus and potassium fertilizers had no obvious influence on the anthraquinone content of R. tanguticum at the same harvesting stage.