The impact of boron excess and vermicompost tea on the arsenic absorption by Atriplex atacamensis PHIL

Details

Supervisors

Lutts, Stanley

Faculty

Faculté des bioingénieurs

Degree label

Master [120] : bioingénieur en sciences et technologies de l'environnement

Abstract

The Atacama Desert, in Northern Chile, is one of the most arid place in the world. Some regions like the Quillagua oasis are highly contaminated by As and B. In addition to natural reasons, mining activities are the cause of the increasing contamination of the unique source of water, the Rio Loa river. A. atacamenis is a xerohalophyte plant species endemic of this region. This plant is almost the only species able to survive in these very harsh conditions. Previous researches have mentioned its potential for phytostabilisation applications of As-contaminated soils since the plant is able to accumulate As in its roots. The plant can also deal with an excess of B but the behaviour of the plant simultaneously exposed to As toxicity and B excess has not yet been explored. On the other hand, vermicompost is subject to growing curiosity in the scientific community. This consists in the digestion product of organic matter by earthworms. It contains interesting chemicals and is known to act as a biostimulant. Its beneficial effects on plant growth, biotic and abiotic stresses have already been observed. However, the effect of vermicompost on metal stress is poorly documented. The present study aims to highlight these gaps; its first objective is to provide the global composition of the vermicompost tea (VCT) used, the second to identify the effect of B excess and VCT on As absorption by A. atacamensis. To carry out this experiment, A. atacamensis were grown in hydroponic culture. Half of plants were treated with 10% in volume of VCT, kindly provided by the company PUR VER®. As (500 M; in the form of arsenate) and B (500 mg.L-1) were applied separately or simultaneously. The eight treatments (Control, As, B and As+B, with and without VCT) lasted two weeks. VCT composition was analysed in detail. Leaves and roots masses and WC were measured as well as ions content. Two osmoprotectants, proline and GB, were quantified. MDA, GSH, PCs, total phenolics and flavonoids concentrations were also quantified in leaves and roots. Results confirm the resistance of the plant to such As concentration but the B concentration applied induced a high level of plant mortality. Surviving plants, however, efficiently produced osmoprotectants and were able to maintain the WC. B significantly decreased the As content while As increased B content in the plant. B induced a high oxidative stress and plants mitigated it by producing antioxidants while As was mainly complexed with PCs. VCT did not have significant impact on plant growth and WC but improve plant tolerance to accumulated ions. It drastically decreased the proline concentration probably by having an effect on the internal signalling pathway. VCT contains numerous phytohormones (ABA, CK, SA,…) putatively involved in plant resistance against abiotic stress. It increased B translocation to aerial parts without affecting the MDA concentration. VCT increased the antioxidant activity of the plant and thereby help it to resist metal stress. VCT thiols rich compounds may modify the As speciation decreasing its bioavailability. It is concluded that Atriplex atacamensis is a promising species for phytomanagement of B and As-contaminated areas and that VCT is a useful tool to improve its level of stress tolerance.