Copper contamination in false yellowhead-colonized soils: complementary metabolomic and taxonomic analyses suggest candidate microbial and chemical biomarkers.

Long-term use of Bordeaux mixture in French vineyards has led to elevated copper levels in soils, many of which are now colonised by false yellowhead after vineyard abandonment. This species provides a relevant model to study plant-soil interactions under copper stress. This study investigated how soil copper contamination affects plant growth in microcosms, focusing on rhizosphere microbial communities and plant metabolomic responses. A complementary approach combining metabarcoding and untargeted metabolomics was used to identify candidate biomarkers of copper contamination. Copper levels were quantified in soils, roots and leaves. The results highlighted altered plant morphology, particularly reduced root growth and copper sequestration in roots. Microbial analyses showed an enrichment of Actinobacteria at the class level and Frankiales at the order level in highly contaminated soils, while Polyangia at the class level dominated uncontaminated soils. Metabolomic profiling highlighted flavonoids, quinic acid derivatives and sesquiterpenes as key chemical markers of copper stress. By integrating microbial and chemical indicators within a soil-plant-microbial microcosm, this study demonstrates the added value of a complementary approach for describing potential metal-specific stress signatures. This study proposes candidate biomarkers for environmental monitoring in false yellowhead and provides perspectives for assessing biosolution effects on copper-induced abiotic stress in agricultural systems.