The performance of Fraxinus angustifolia as a helper for metal phytoremediation programs and its relation to the endophytic bacterial communities

Abstract

Soil contamination with metals is a serious problem requiring urgent measures to counteract their impacts. The conventional soil remediation techniques are often inefficient and expensive. In this work, we studied the potential of the species Fraxinus angustifolia for the phytoremediation of metal contaminated soils from the Cunha Baixa uranium mine (Mangualde, Portugal). The plants were exposed to a contaminated, a reference and a control soil, for a period of about 3months, during which metal accumulation and a set of physiologic parameters (shoot height, potential maximum efficiency of PSII (Fv/Fm) and quantum yield of PSII (ΦPSII), leaf area, specific leaf area, leaf relative water content, leaf chlorophyll a, chlorophyll b and carotenoid content, leaf malondialdehyde (MDA) content and leaf proline content) were measured. The genetic profiles of the endophytic communities from the roots of the plants were also analyzed, via PCR-Denaturing Gradient Gel Electrophoresis (DGGE) targeted for a conserved region of 16S rDNA, pre- and post-exposure. Only the shoot height was a suitable indicator of the negative effects of the contamination with metals on the plants. The remaining parameters indicated good physiologic fitness and recovery. The trees did not hyperaccumulate metals but extracted Sr at a higher rate. The bacterial profiles from the control and reference soils showed more similarity with each other and with the pre-exposure profiles than with those from the contaminated soil. We showed that F. angustifolia has the ability to resist and adapt to the adverse conditions of contamination, revealing a potential which can be exploited for phytoremediation, specifically phytostabilization. It also revealed that changes exerted on the bacterial root communities exposed to contamination, resulted in profiles considerably different from those of the remaining communities.