The scientific objective is to search for plants suitable for phytoremediation and to describe their functioning, in order to model their cultivation. Moreover, it is necessary to understand the interactions between the pollutants and the soil components, to describe the fluxes of pollutants from soil to plant organs as well as the fate of organic pollutants in the rhizosphere. If this research firstly aims to create phytoremediation applications, it also constitutes a way of better understanding the dynamics of pollutants in any cultivated ecosystem. This Theme is at present, divided into two Sub-Themes
The control of phytodegradation and of phytoextraction depends on a description of the processes involved in the bioavailability of pollutants in soils. These processes take place in the soil zone under the influence of roots, namely the rhizosphere. The physical, chemical and biochemical conditions of the rhizosphere differ from those of the soil without roots because of the growth of the latter, of their water and solute uptake, their respiration and because of the rhizodeposition. Thus, rhizosphere is characterized by a high organic carbon concentration, a strong biological activity and pronounced pH and moisture variations.
The works Sub-Theme II are carried out on the scale of the soil aggregate and of the root and take into account physical, chemical and biological factors. They aim to describe the mechanisms of sorption, dissolution, transport, absorption (mainly for trace elements) and degradation (organic molecules), including the effect of dissolved organic carbon, particularly of root exudates. The objective is to model (i) the fluxes of trace elements towards the roots and (ii) the functioning of the rhizosphere as a reactor which degrades organic molecules.
This Sub-theme gathers together research work aiming to model, as functions of climate, soil and cultivation variables:
The results of this research, associated with those of Sub-Theme II.1 will be integrated into a culture model built as an engineering tool for phytoremediation.
Concerning mineral pollutants, the experimental models are cadmium (Cd) and nickel (Ni). Polycyclic Aromatic Hydrocarbons represent the organic xenobiotics.
Plants with contrasting physiology regarding pollutants are used: on one hand, hyper-accumulating species like Alpine pennycress (Thlaspi caerulescens) or yellowtuft (Alyssum murale), on the other hand non-accumulating cultivated species such as maize (Zea mays).