Morphological and functional responses of a metal-tolerant sunflower mutant line to a copper-contaminated soil series

Abstract

The potential use of a metal-tolerant sunflower mutant line for biomonitoring Cu phytoavailability, Cu-induced soil phytotoxicity, and Cu phytoextraction was assessed on a Cu-contaminated soil series (13–1020 mg Cu kg⁻¹) obtained by fading a sandy topsoil from a wood preservation site with a similar uncontaminated soil. Morphological and functional plant responses as well as shoot, leaf, and root ionomes were measured after a 1-month pot experiment. Hypocotyl length, shoot and root dry weight (DW) yields, and leaf area gradually decreased as soil Cu exposure rose. Their dose-response curves (DRC) plotted against indicators of Cu exposure were generally well fitted by sigmoidal curves. The half-maximal effective concentration (EC₅₀) of morphological parameters ranged between 203 and 333 mg Cu kg⁻¹ soil, corresponding to 290–430 μg Cu L⁻¹ in the soil pore water, and 20 ± 5 mg Cu kg⁻¹ DW in the shoots. The EC₁₀ for shoot Cu concentration (13–15 mg Cu kg⁻¹ DW) coincided to 166 mg Cu kg⁻¹ soil. Total chlorophyll content and total antioxidant capacity (TAC) were early biomarkers (EC₁₀: 23 and 51 mg Cu kg⁻¹ soil). Their DRC displayed a biphasic response. Photosynthetic pigment contents, e.g., carotenoids, correlated with TAC. Ionome was changed in Cu-stressed roots, shoots, and leaves. Shoot Cu removal peaked roughly at 280 μg Cu L⁻¹ in the soil pore water.