How can a rare protected plant cope with the metal and metalloid soil pollution resulting from past industrial activities? Phytometabolites, antioxidant activities and root symbiosis involved in the metal tolerance of Astragalus tragacantha

Marie-Dominique Salducci,Hélène Folzer,Julien Issartel,Jacques Rabier,Véronique Masotti,Pascale Prudent,Laurence Affre,Laurent Hardion,Thierry Tatoni,Isabelle Laffont-Schwob

doi:10.1016/j.chemosphere.2018.11.078

Abstract

Astragalus tragacantha is a protected plant species in France that grows even in the trace metal and metalloid (TMM) polluted soils of the Calanques National Park (PNCal). Soils are mainly contaminated by lead, copper, zinc and arsenic. An ex situ experiment was conducted, firstly to determine the molecular responses and root traits involved in the TMM tolerance of this plant species by growing individuals in a soil from the surroundings of one of the brownfields of the PNCal, known as l’Escalette, where this plant species grows spontaneously. Secondly, in order to determine the plasticity of these responses, seeds were collected from three different populations, at l’Escalette (polluted site), one from the Frioul archipelago (non-polluted, insular site) and one from La Seyne (non-polluted, littoral site). The results of this study confirmed the capacity of A. tragacantha to germinate and grow in TMM contaminated soils. Only moderate significant variations in chlorophyll and flavonol indices, proline content and antioxidant activities were detected between polluted and control soil conditions for all populations. The main driver for A. tragacantha TMM tolerance seemed to be its ability to be associated with root symbionts i.e. arbuscular mycorrhizal fungi and dark septate endophytes, corresponding to a nutrient-uptake strategy trait. This work provides support for the challenge of A. tragacantha conservation along the littoral of the PNCal, because increasing the number of A. tragacantha individuals would both increase vegetation cover of the polluted soils to reduce the pollution transfer and reinforce the populations of this species.

Highlights

Trace metal and metalloid (TMM) contamination of soil, water and atmosphere is of worldwide concern (Mcintyre, 2003)
The composite soil (SPO) used for the controlled condition culture experiment was highly contaminated by Pb and As (Table 1), with up to 170-fold more contaminated with Pb and up to 45-fold with As than the less anthropized soils of Frioul archipelago (FRI) and VAR A. tragacantha populations, and 3-fold more contaminated with Pb and 6-fold with As than the soil from the Escalette population (ESC)
Affholder et al (2014) suggest that arbuscular mycorrhizal (AM) fungi and dark septate endophytes (DSE) associated with the roots of native Rosmarinus officinalis individuals contribute to their TMM tolerance in the same pollution context in the Calanques National Park

Summary

Introduction

Trace metal and metalloid (TMM) contamination of soil, water and atmosphere is of worldwide concern (Mcintyre, 2003). The metallurgy industry in the past led to TMM pollution of surrounding soils. Some brownfields are partially covered by spontaneous vegetation that probably developed several mechanisms of metal tolerance, enabling its survival in such a harsh environment. Spontaneously vegetated brownfields provide a pool of TMM tolerant plant individuals healthy enough to maintain a self-sustaining population and to enable us to refine in situ mechanisms of TMM tolerance. When a species establishes on a soil with high TMM content, plant tolerance to TMM will occur within the limits of phenotypic plasticity (Schat et al, 1997; Pollard et al, 2002; Ernst, 2006; Quintela-Sabarís et al, 2012)

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