Advantages and limits to copper phytoextraction in vineyards

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.

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.

Drivers to improve metal(loid) phytoextraction with a focus on microbial degradation of dissolved organic matter in soils

Bioaugmentation of soils can increase the mobilization of metal(loid)s from the soil-bearing phases. However, once desorbed, these metal(loid)s are mostly complexed to the dissolved organic matter (DOM) in the soil solution, which can restrict their availability to plants (roots mainly taking up the free forms) and then the phytoextraction performances. Firstly the main drivers influencing phytoextraction are reminded, then the review focuses on the DOM role. After having reminding the origin, the chemical structure and the lability of DOM, the pool of stable DOM (the most abundant in the soil) most involved in the complexation of metal(loid)s is addressed in particular by focusing on carboxylic and/or phenolic groups and factors controlling metal(loid) complexation with DOM. Finally, this review addresses the ability of microorganisms to degrade metal(loid)-DOM complexes as an additional lever for increasing the pool of free metal(loid) ions, and then phytoextraction performances, and details the origin of microorganisms and how they are selected. The development of innovative processes including the use of these DOM-degrading microorganisms is proposed in perspectives.

Ability of aerated compost tea to increase the mobility and phytoextraction of copper in vineyard soil

Aerated compost tea (ACT) contains soluble humic substances (SHS) that are expected to alter the dynamics and ecotoxicity of Cu in soil. This study investigated the efficiency of ACT in enhancing the mobility and phytoextraction of Cu in vineyard soil. Crimson clover (Trifolium incarnatum L.) was grown on a vineyard soil at three concentrations of Cu (90, 261 and 432 mg kg^-1), and supplied (or not) with ACT, then sampled after 56 days to determine the amount of Cu phytoextracted. Soil was extracted with 0.01 M KCl and potentiometric analyses were performed to measure the impact of ACT on the speciation of Cu in the extraction solution. ACT was found to increase the mobility of Cu in the soil by a factor of 3-14 depending on the soil Cu content and on the soil extraction date. The increase in Cu mobility was associated with an increase in absorbance at 254 nm and with a decrease in the free ionic fraction of Cu in the KCl extract, suggesting that Cu was mainly mobilized by the SHS present in the compost tea, and through a ligand-controlled dissolution process. ACT increased Cu phytoextraction at Cu90 and Cu261 by on average 80% thanks to its positive impact on plant growth, and on Cu accumulation in plant shoots, whereas it reduced Cu phytoextraction at Cu432 due to its deleterious effect on plant growth at this soil Cu content. ACT is thus an efficient way to increase the phytoavailability of Cu in soil, but probably should not be used in vineyard soils that are highly contaminated by Cu. To obtain Cu phytoextraction yields in line with the needs of the wine sector, the use of ACT needs to be associated with the cultivation of a Cu-accumulating plant.