Coupled effects of CO2 and biochar amendment on the yield and quality of Pseudostellaria heterophylla

Abstract

Previous studies reveal that atmospheric CO2 enrichment can improve plant growth with enhanced photosynthesis. However, it is not well-understood whether biochar could be coupled with elevated CO2 to further promote growth and quality of medicinal plants. This study aims to investigate the interactive effects of CO2 enrichment and biochar amendment on the growth and quality of a common medicinal plant (Pseudostellaria heterophylla (Miq.) Pax). Two CO2 concentrations (400 and 1000 ppm) and three biochar dosages (0, 3% and 5%) were considered and tested. Compared with the control in the ambient CO2 without biochar addition, coupled CO2 enrichment and 3% biochar enhanced available nutrient levels (e.g., P) most efficiently by up to 1740% in rhizosphere. This was due to the increased soil enzyme activity and relative abundance of beneficial bacteria for nutrient activation. Elevated CO2 (1000 ppm) coupled with 3% biochar induced the highest tuber yield of P. heterophylla, which was 228% higher than the control. Coupled elevated CO2 and 5% biochar group shows an increasing yield by 84%. The coupled treatments could increase the yield by up to 213% as compared with the only biochar or only elevated CO2 treated groups. The concentrations of polysaccharides in root tuber were improved by 56–124% under the CO2 enrichment. They all satisfy the requirements of Hong Kong Chinese Materia Medica Standards. However, the concentrations of saponins decreased by 14–20% in low dosages of biochar treated groups (0, 3%) under the elevated CO2 concentration, as compared with those under the ambient CO2. On the contrary, CO2 enrichment increased the concentrations of saponins by 22% when biochar dosage increased to 5%. This study recommends that 3% biochar amendment coupled with 1000 ppm CO2 should be adopted to enhance the yield and biosynthesis of polysaccharides in root tuber of P. heterophylla.