Root and Shoot Response to Nickel in Hyperaccumulator and Non-Hyperaccumulator Species

Abstract

The soil-root interface is the micro-ecosystem where roots uptake metals. However, less than 10% of hyperaccumulators' rhizosphere has been examined. The present study evaluated the root and shoot response to nickel in hyperaccumulator and non-hyperaccumulator species, through the analysis of root surface and biomass and the ecophysiological response of the related aboveground biomass. Ni-hyperaccumulators <i>Alyssoides utriculata</i> (L.) Medik. and <i>Noccaea caerulescens</i> (J. Presl and C. Presl) F.K. Mey. and non-hyperaccumulators <i>Alyssum montanum</i> L. and <i>Thlaspi arvense</i> L. were grown in pot on Ni-spiked soil (0-1000 mg Ni kg^-1, total). Development of root surfaces was analysed with ImageJ; fresh and dry root biomass was determined. Photosynthetic efficiency was performed by analysing the fluorescence of chlorophyll a to estimate the plants' physiological conditions at the end of the treatment. Hyperaccumulators did not show a Ni-dependent decrease in root surfaces and biomass (except Ni 1000 mg kg^-1 for <i>N. caerulescens</i>). The non-hyperaccumulator <i>A. montanum</i> suffers metal stress which threatens plant development, while the excluder <i>T. arvense</i> exhibits a positive ecophysiological response to Ni. The analysis of the root system, as a component of the rhizosphere, help to clarify the response to soil nickel and plant development under metal stress for bioremediation purposes.