Copper accumulation in five weed species commonly found in the understory vegetation of Mediterranean vineyards.

Copper (Cu) concentration in agricultural soils often exceeds toxicological limits due to application of Cu-based fungicides. The potential of weeds for their use as functional cover plants in vineyard management and phytoremediation practices is little explored. We identified five weed species widely present in vineyards and assessed their Cu accumulation from eleven Mediterranean vineyards (soil Cu: 60-327 µg g-1) and two adjacent control sites (soil Cu: 15-30 µg g-1). Soils and plants were characterized by their physico-chemical properties and nutrient content. We applied multivariate techniques to analyze relationships between soil properties and leaf nutrient composition. Copper tolerance and accumulation traits were further tested in hydroponics using a series of CuSO4 concentrations (0.1-16 µM). Under field conditions, the highest Cu concentration in both roots and leaves were found in Lolium perenne (221 and 461 µg g-1, respectively), followed by Plantago lanceolata, Rumex obtusifolius and Taraxacum officinale (>100 µg g-1 Cu in leaves). Only one species, Trifolium repens, did not accumulate remarkable Cu concentrations. Overall, and as revealed by the multivariate analyses, leaf Cu concentration was driven by soil Cu content, soil texture, organic matter, nitrogen, and Cu uptake into roots. However, functional regression analysis and controlled experiments suggested that Cu might be additionally absorbed from the deposits on the leaf surface related to the Cu-fungicide treatments and soil dust. Our study highlights the importance of intra-specific variability in Cu accumulation among weed species in Cu-contaminated agricultural soils. Further validation of these findings under controlled conditions could provide essential insights for optimizing management and remediation strategies.

Independent variation in copper tolerance and copper accumulation among crop species and varieties.

Copper (Cu) locally contaminates soils and might negatively affect growth and yield of crops. A better understanding of plant copper tolerance and accumulation is needed in order to breed more Cu-tolerant or Cu-efficient crops. Cu tolerance was evaluated in different varieties of seven species (Brassica carinata, B. juncea, B. napus, Cynara cardunculus, Helianthus annuus, Nicotiana tabacum and Raphanus sativus) exposed to a series of CuSO4 concentrations (0.1-8 µM CuSO4) in the nutrient solution. Plants were further exposed to 0.1 µM CuSO4 and to their variety-specific concentrations that reduced root growth to 50% of the maximum rate (EC50). Among all the varieties of all the species the EC50 varied from 0.7 up to 3.1 µM Cu. B. carinata was significantly more Cu-sensitive than the other species, which were not significantly different among each other, and B. carinata and H. annuus accommodated significant intra-specific, inter-varietal variation. There were significant differences between species in Cu uptake efficiency and nutrient status. When under EC50 exposure, all the Brassicaceae, except B. carinata, maintained low Cu concentrations in shoots, whereas the other species and B. carinata exhibited significantly increased shoot Cu concentrations, compared to the control. There was no apparent relationship between Cu tolerance and Cu accumulation in roots and shoots, suggesting that the observed variation in tolerance, both between and within species, is not explained by differential exclusion capacity. Discriminant analysis and treatment comparisons suggest possible contribution of lignin, saturated fatty acids, manganese (Mn) and zinc (Zn) in tolerance to high Cu concentrations in shoot.