Thermophysiological responses of ginseng to abnormal season-long high temperature

Physiological responses of ginseng (Panax ginseng) were investigated under abnormal season-long high-temperature environmental conditions for obtaining vulnerability assessment data. Soil-plant-atmosphere research chambers were used to employ the + 2, +4, and + 6 elevated temperature conditions (ETC) from June to August compared to hourly-averaged air temperatures for the past 10 years (from 2010 to 2019) in Eumseong, Korea. Under the ETC, secondary growth and development of taproots were significantly inhibited due to the reduction of photosynthetic efficiency with chlorophyll destruction. The net photosynthetic rate at the light saturation point (A_max) decreased and the dark respiration rate (R_d) increased as the air temperature increased. Consequently, carbohydrate deposition in the storage parenchyma of the taproots decreased over time. The roots at harvest were severely rotten under + 6 ETC. The harvested root weights decreased by 60.1, 21.4, and 12.3% under + 6, +4, and + 2 ETC, respectively, compared to those under control conditions. Under + 2 and + 4 ETC, total ginsenoside content (TGC) in roots was similar, but under + 6 ETC, TGC significantly increased with the increases of the panaxatriol type ginsenoside Re and the panaxadiol types ginsenosides such as Rb₂, Rb₃, and Rd. These results suggest that developing high-temperature stress adaptation technologies should be considered frequent abnormally high-temperature environments caused by global climate change.