Nickel hyperaccumulating plants: strategies to improve phytoextraction and a characterisation of Alyssum endemic to the Iberian Peninsula

Abstract

The metal hyperaccumulating species play an important role in soil phytoremediation techniques. The Thesis Project focuses on the development of various methods to improve the ability of nickel phytoextraction in hyperaccumulating species. There are a variety of techniques used for this purpose. This study focuses primarily on the use of agricultural practices to increase the bioavailability of metals in soil, inoculation of plants with microorganisms involved in the process of phytoextraction and external application of growth promoting substances in the plant. Through the development of these techniques is possible to obtain plants with a greater potential for phytoextraction of heavy metals and therefore most likely to use in soil remediation. In this study is also included the study of five different populations of the nickel hyperaccumulator Alyssum serpyllifolium (ssp. lusitanicum and ssp. malacitanum) of the Iberian Peninsula (also known as A. pintodasilvae and A. malacitanum). Different populations included in this study represent the main serpentinitic areas of the Iberian Peninsula: the region of Tras-os-Montes (Morais and Samil) in the northeastern Portugal, Melide in the province of A Coruña, and Sierra de Aguas and Sierra Bermeja, located in the province of Malaga. The main conclusions of this Thesis can be summarised as: - The application of plant growth regulators (PGRs) or phytohormones may increase biomass production of Ni hyperaccumulating species such as Alyssum and Noccaea and, consequently, their metal phytoextraction capacity. The most effective PGR for enhancing Ni removal was the IAA-based product. - Bioagumentation using PGPR can be considered as a potential tool to optimised Ni phytoextraction (or phytomining) technologies, but it remains to be seen whether or not plant-associated microorganisms can further improve the shoot Ni removal on a field scale. This study has identified candidate strains which hence, could be useful for future field-based trials. - There is a great variability in biomass production and Ni accumulation between and within the different A. serpyllifolium populations. A better knowledge of the causes and factors involves in the inter- and intra-population variability in Ni-hyperaccumulating Alyssum species can be an useful tool to select populations more efficient for phytoextraction/phytomining technologies.