PhD thesis defence Ruoyu HU

Thesis defence title: " Mobility and transfer of rare earth elements from soil to plants by arbuscular mycorrhizal fungi". The work has been carried out at  “Laboratoire Interdisciplinaire des Environnements Continentaux” (LIEC UMR 7360) under the supervision of Dr Corinne LEYVAL.

The Thesis defence will take place on Wednesday, March 10th, 2021, at 9.00 am (GMT+1) in Nancy. The defence will be transmitted by video conference. The link will be sent next week.

The members of the jury are as follows:

Reviewer Mr Erik JONER                                     Research Director, Nibio, Ås - Norway

Reviewer Mr Thierry LEBEAU                            Professor, University of Nantes - France

Examiner Mr Alexis DE JUNET                           Senior Lecturer, University of Lorraine - France

Examiner Ms Laure GIAMBÉRINI                      Professor, University of Lorraine - France

Examiner Ms Nathalie SÉJALON DELMAS       Senior Lecturer, Paul Sabatier University – France

Examiner Mr Ye-Tao TANG                                 Professor, Sun Yat-sen University - China

Director Ms Corinne LEYVAL                             CNRS Research Director, University of Lorraine - France

The PhD work will be presented in English. Here is the abstract of the thesis in English and French

Abstract

Mobility and transfer of rare earth elements from soil to plants by arbuscular mycorrhizal fungi

Rare earth elements (REE) are a group of strategic metals that have been widely used in modern technologies in recent decades. However, due to the corresponding REE emission from industries and the over-exploitation, large amounts of anthropogenic rare earth can accumulate in the environment, and be phytotoxic. Arbuscular mycorrhizae (AM) benefit to plants in metal-contaminated soils by improving their survival and growth and alleviating metal toxicity, but little information is available about soil contaminated by rare earth elements. The objective of this PhD project is to understand the transfer of REEs from soil to plants and especially the role of AM fungi on plant growth and REE transfer to plants in REE contaminated soils. Experiments were launched using a model legume plant alfalfa (Medicago sativa), a model REE samarium (Sm), and a metal-tolerant Funneliformis mosseae fungus in a growth chamber. We first studied the bioavailability and transfer of an REE to Medicago sativa grown on two contaminated soils differing in their chemical characteristics. The results showed that DTPA extractable Sm was well correlated with Sm uptake in alfalfa shoots. Although the soil to plant transfer factor was low, alfalfa biomass was reduced when the soils were spiked with 100 to 200 mg kg-1 of Sm. Then the hypothesis was drawn that arbuscular mycorrhizal fungi might protect the plant against REE toxicity. Therefore, a pot experiment was launched to study the role of AM fungi on alfalfa growth and a compartment experiment was performed to study the transfer of Sm to alfalfa via AM fungal hyphae. The biomass of alfalfa grown on Sm-spiked soil was significantly higher following arbuscular mycorrhiza inoculation. P content was also higher in mycorrhizal than nonmycorrhizal plants, but there was no significant Sm transfer to the plant by F.mosseae. Since there are often multiple REEs in contaminated soils, including light (LREE) and heavy (HREE) REEs, a compartment experiment was launched using 4 REEs, alfalfa and ryegrass, which confirmed that there was no transfer of the 4 REEs to alfalfa plants by F.mosseae. Finally, an REE mining soil collected from China was used to analyze the toxicity of REEs to AM fungal spores and to leek plants inoculated or not with the AM fungus, using spore germination assays and a plant growth experiment. The high concentration of REEs significantly inhibited plant growth and spore germination rate, and the fungus tolerated relatively high REE concentrations, but there was no significant difference in REE tolerance between the two isolates of F.mosseae. Other fungi and plants should be tested, and field experiments performed, but our results suggest that arbuscular mycorrhizal plants might be considered in phytorestoration of REE-contaminated soils.