Thesis defense of Justine Garraud – “Reducing the copper load in vineyard soils by phytoextraction combined with bioaugmentation” – at 9 a.m. LPG Nantes

The repeated use of copper (Cu)-based fungicides has led to its accumulation in wine-growing soils. Phytoextraction allows reducing their Cu load. In the soil solution, Cu is however mainly complexed with dissolved organic matter (DOM), which shows low plant availability. The work carried out in this PhD thesis aims to (i) select a Cu-accumulating plant that can be used to feed animals and (ii) increase the pool of plant-available Cu by bioaugmentation of the soil. Among the 7 plants tested in hydroponics (oats, hemp, chicory, brown mustard, ryegrass, buckwheat and sunflower), chicory accumulated the most Cu in its harvestable parts. A bacterial isolate and a bacterial consortium were tested to i) mobilize Cu from soil bearing phases, ii) degrade Cu-MOD complexes and iii) increase plant growth. The isolate Pseudomonas sp. 171 (P171) was used for its PGPR (plant growth promoting rhizobacteria) and Cu mobilization properties. In contrast, no bacteria capable of degrading MOD were clearly identified. To improve the survival of P171, potential partners were identified by association networks. A consortium composed of Flavobacterium (isolate F47-2) and P171 was tested by growing chicory on wine-growing soil bioaugmented with this consortium (in free form or immobilized in alginate beads). Chicory accumulated more copper with the consortium than with P171. Monitoring of P171 by the GFP gene and by metabarcoding of the rpoB and 16S genes also showed that immobilization of this consortium favored the installation of P171 in the soil.