Cover crop response to increased concentrations of copper in vineyard soils: Implications for copper phytoextraction

The use of cover crops (CCs) in viticulture is threatened by the contamination of vineyard soils by copper (Cu). This study investigated the response of CCs to increased concentrations of Cu in soil as a way to assess their sensitivity to Cu and their Cu phytoextraction ability. Our first experiment used microplots to compare the effect of increasing soil Cu content from 90 to 204 mg kg^-1 on the growth, Cu accumulation level, and elemental profile of six CC species (Brassicaceae, Fabaceae and Poaceae) commonly sown in vineyard inter-row. The second experiment quantified the amount of Cu exported by a mixture of CCs in vineyards with contrasted soil characteristics. Experiment 1 showed that increasing the soil Cu content from 90 to 204 mg kg^-1 was detrimental to the growth of Brassicaceae and faba bean. The elemental composition of plant tissues was specific to each CC and almost no change in composition resulted from the increase in soil Cu content. Crimson clover was the most promising CC for Cu phytoextraction as it produced the most aboveground biomass, and, along with faba bean, accumulated the highest concentration of Cu in its shoots. Experiment 2 showed that the amount of Cu extracted by CCs depended on the availability of Cu in the topsoil and CC growth in the vineyard, and ranged from 25 to 166 g per hectare. Taken together, these results emphasize the fact that the use of CCs in vineyards may be jeopardised by the contamination of soils by Cu, and that the amount of Cu exported by CCs is not sufficiently high to offset the amount of Cu supplied by Cu-based fungicides. Recommendations are provided for maximizing the environmental benefits provided by CCs in Cu-contaminated vineyard soils.