Relationships among soil characteristics,plant macronutrients,and cardenolide accumulation in natural populations of Digitalis obscura

In the present study, we have investigated relationships among several soil parameters (pH, organic matter, total carbonate, macronutrients, electrical conductivity, cation‐exchange capacity) and macronutrient and cardenolide contents in leaves of wild Digitalis obscura plants. Young and mature leaves and soil samples were collected in ten different areas, corresponding to three Mediterranean bioclimatic belts (thermo‐, meso‐, and supramediterranean belts). Soil and leaf macronutrient (N, P, K, Ca, and Mg) contents and leaf cardenolide contents were determined. Bioclimatic conditions influenced the development of D. obscura, biomass being lowest in plant populations of the supramediterranean belt, but they did not exert any relevant effect on the contents of macronutrients in soils and plants. Magnesium (total and EDTA‐extracted) was the only soil macronutrient significantly correlated with its content in the plant. Cardenolide contents were negatively correlated with the N, P, and K contents in young leaves, whereas such correlations were highly significant and positive for Mg.