Mémoire

Abstract

Soil contamination by metal(loid)s is a widespread legacy of past industrial activities in Wallonia and represents a major environmental challenge, threatening the ecosystem services provided by soils. Phytomanagement offers a plant-based rehabilitation approach that aims to mitigate environmental risks associated with contaminated soils while enabling biomass production and the restoration of soil ecosystem services. This Master thesis aimed to contribute to the development of phytomanagement strategies for contaminated soils in Wallonia within the frameworks of the Plant4Wasteland and IASIS projects, through soil characterisation, amendment testing, plant performance evaluation and microbial isolation to obtain potential plant growth–promoting bacteria adapted to metal(loid)-contaminated soils. Four post-industrial sites in Wallonia were characterised in terms of their physicochemical properties and metal(loid) contamination. Elevated concentrations exceeding regional threshold values were identified at three sites, whereas one site showed no pronounced contamination. Despite high total metal(loid) concentrations, bioavailable fractions were generally low, largely influenced by alkaline pH conditions. However, strong spatial heterogeneity, nutrient imbalances and limited buffering capacity emerged as key constraints for plant establishment and phytomanagement implementation. At one of the four sites, within the IASIS project, a field experiment was conducted using three industrial crop species (Cannabis sativa, Camelina sativa and Crambe abyssinica), vermicompost soil amendment and a foliar amino acid–based biostimulant to evaluate the application of phytomanagement for biomass production at the site. Vermicompost had previously been identified as the most suitable soil amendment in a preliminary greenhouse experiment, where it significantly enhanced plant growth, biomass production and plant health of Camelina sativa and Crambe abyssinica. Initial field assessments confirmed the strong influence of soil heterogeneity on plant performance. Crambe abyssinica showed the weakest overall performance, Camelina sativa achieved satisfactory results only under vermicompost application, and Cannabis sativa demonstrated high stress tolerance and rapid biomass production. Vermicompost application under field conditions had an overall positive effect on plant development, whereas the foliar application of the amino acid–based biostimulant did not improve plant performance for any of the three species. In parallel to the field experiment, rhizospheric and root-associated microorganisms were successfully isolated from Crambe abyssinica grown on soil from the contaminated site, providing a foundation for the future development of site-adapted plant growth–promoting microbial consortia.