In extreme environments, plants and microorganisms adapt and implement strategies to develop despite the constraints imposed by the environment. We propose to study the bio-physical-chemical mechanisms of transfer and transformation of trace elements on a site rich in certain rare elements, called "High Tech » metals" (HTM).
The Jas Roux site in the Hautes Alpes (Ecrins National Park, Chapelle en V.) is a hydrothermal site, located between 2130 and 2250 m altitude over a width of about 500 m, which is characterized by a complex mineralogical assemblage of lead, silver and thallium sulphosalts also containing gallium, tungsten and rare earths elements (e.g. Nd, Y). The high HTM contents are naturally occurring and vary along a gradient related to the slope of the site.
A first field campaign revealed the presence of Ga, Sb, Nd, Tl, Ag and W in the soils at concentrations between 10 and 300 ppm, higher or much higher than in uncontaminated soils. A first inventory of plants on a plot (9 m2) at the top of the profile indicates a classical diversity of alpine ecosystems. 65 species were identified, including thalium (Tl) accumulators and hyperaccumulators (Biscutella laevigata, Minuartia verna, Vaccinium myrtillus), but also grasses like fescue. Tl, for example, is known to be one of the most toxic contaminants to living organisms, comparable to lead or mercury (Peter and Viraraghavan, 2005). Plants growing on these soils have developed various tolerance processes such as exclusion mechanisms within the rhizosphere or detoxification mechanisms in planta. Data on the biogeochemical cycle of Tl in terrestrial ecosystems are very incomplete, especially concerning soil-plant transfer, tolerance mechanisms, speciation within plants, impact on soil biological life. However, the use of HTMs has been increasing in recent years. Tl has applications in semiconductors, gamma radiation detectors, glasses to increase their refractive index. Recent developments include high temperature superconducting materials for magnetic resonance imaging (Kelly and Matos, 2013). Increased use of HTMs induces a greater likelihood of accidental release into the environment, but the consequences on environments remain difficult to predict as little data exists on the behavior of these elements.The overall objective of this project is to identify the mechanisms that control metal mobility, speciation, and bioavailability within the rhizosphere in order to answer the following question: Do plants have adaptive processes to high metal/metalloid concentrations?
The project aims to increase our level of knowledge on :