Assessment of halophyte plant phenotypic responses under heavy metals pollution. Implications for monitoring and phytoremediation.

While phytoremediation is a highly valued practice to address local pollution problems, the use of early biomarkers of stress is useful for monitoring environments since they allow us to take measures before deleterious effects are irreversible. In this framework the goals are: to evaluate the pattern of leaf shape variation of Limonium brasiliense plants related to a metal soil gradient in the San Antonio salt marsh; to assess whether seeds from sites with different pollution levels show the same pattern of leaf shape variations under optimal growing conditions; and to compare the growth, the Pb accumulation pattern, and the leaf shape variation pattern of plants germinated from seeds originated in sites with different pollution levels in response to an experimental Pb rise. The results obtained from leaves collected in the field showed that the leaf shape changed depending on the soil metal levels. Plants germinated from seeds collected at the different sites expressed all the variation in leaf shape independently of the origin site, and the mean shape of each site was close to the consensus. Instead, when looking for the leaf shape components that maximize the differences between the sites from a growth experiment exposed to an increase in Pb in the irrigation solution, the pattern of variation found in the field disappeared. That is, only plants from the polluted site did not show variations in leaf shape in response to Pb additions. Finally, Pb accumulation in the roots was highest in plants germinated from seeds from the site where the soil pollution is greater. That suggests that seeds of L. brasiliense from polluted sites are better to use in phytoremediation practices, specifically to stabilize Pb in its roots whilst plants from the non-polluted site are better to detect pollutant soils using the leaf shape as an early biomarker.