Soil moisture influences low larkspur and death camas alkaloid levels.

Abstract

It has long been known that alkaloid composition and concentration in plants are affected by the stage of growth and by factors at the growing site of the plant. There is, however, a lack of knowledge on the environmental factors that elicit the physiological response of alkaloid-containing plants. A 3-year survey (1992 to 1994) was conducted on the levels of zygacine and methyllycaconitine, the major neurotoxic alkaloids of death camas (Zigadenus venenosus) and low larkspur (Delphinium nuttallianum), respectively. The alkaloid levels of both species do not exhibit diurnal fluctuations, so precise sampling times during the day were not required. Both poisonous species grew in overlapping communities at 2 of the 7 sampling sites. The levels of both types of alkaloids showed similar contrasts at both sites. Lower alkaloid accumulations were associated with site conditions that reduced soil moisture stress and zygacine levels were negatively correlated with soil moisture levels at 6.5 and 14 cm sampling depths. There were no significant correlations or obvious associations between soil temperature and alkaloid levels in either death camas or low larkspur. As expected, higher alkaloid levels were associated with earlier stages of growth in both plants.