Habitat heterogeneity in the pseudometallophyte Arabidopsis halleri and its structuring effect on natural variation of zinc and cadmium hyperaccumulation

Abstract

Arabidopsis halleri is a pseudometallophyte plant model hyperaccumulating zinc and cadmium. This study investigates which abiotic parameters may cause phenotypic divergence among accessions for hyperaccumulation traits. We studied 23 sites from a mining and industrial area in Italian Alps. Sites were characterized for altitude, topographic data, absolute humidity, and accompanying flora. Plant-soil couples were also sampled to measure shoot metal concentrations and soil elemental concentrations, particles size distribution, and pH. Using PLSR analyses, we investigated whether the natural variation in hyperaccumulation abilities could be explained by variation of abiotic parameters. Habitats heterogeneity was high, distinguishing metalliferous and non-metalliferous sites. However, heterogeneity was also observed for soil metal concentrations, particles size distribution and altitude, particularly among metalliferous habitats. This result was supported by floristic data. Soil zinc and cadmium concentrations showed the most contrasting effects on phenotypic divergence between metalliferous and non-metalliferous habitats. However, except for cadmium-related traits in non-metalliferous habitats, other abiotic parameters may affect the variation of zinc or cadmium hyperaccumulation within each habitat type. The classical dichotomous distinction between metalliferous and non-metalliferous habitats may hide the ecological diversity existing within each category for abiotic parameters. This study reveals abiotic parameters that may shape the natural variation of hyperaccumulation abilities.