Cannabis sativa L. growing on heavy metal contaminated soil: Growth, cadmium uptake and photosynthesis

Abstract

The effects of different cadmium concentrations [17 mg(Cd) kg -1(soil) and 72 mg(Cd) kg- 1(soil)] on Cannabis sativa L. growth and photosynthesis were examined. Hemp roots showed a high tolerance to Cd, i.e. more than 800 mg(Cd) kg-1(d.m.) in roots had no major effect on hemp growth, whereas in leaves and stems concentrations of 50 - 100 mg(Cd) kg-1(d.m.) had a strong effect on plant viability and vitality. For control of heavy metal uptake and xylem loading in hemp roots, the soil pH plays a central role. Photosynthetic performance and regulation of light energy consumption were analysed using chlorophyll fluorescence analysis. Seasonal changes in photosynthetic performance were visible in control plants and plants growing on soil with 17 mg(Cd) kg-1(soil). Energy distribution in photosystem 2 is regulated in low and high energy phases that allow optimal use of light and protect photosystem 2 from overexcitation, respectively. Photosynthesis and energy dissipation were negatively influenced by 72 mg(Cd) kg-1(soil). Cd had detrimental effects on chlorophyll synthesis, water splitting apparatus, reaction centre, antenna and energy distribution of PS 2. Under moderate cadmium concentrations, i.e. 17 mg(Cd) kg -1(soil), hemp could preserve growth as well as the photosynthesis apparatus, and long-term acclimation to chronically Cd stress occurred.