THE BIOGEOCHEMICAL BEHAVIOUR OF RARE EARTH ELEMENTS AS A CONSEQUENCE OF PROCESSES OCCURING IN THE VITIS VINIFERA L. – SOIL SYSTEM

The geochemical behaviour of lanthanides and yttrium (Rare Earth Elements, REE) has been investigated mainly in geological systems as the REE exploitation in industrial and agricultural practices is progressively growing in the last years, to such an extent to become strategic materials. Extensive researches evidenced that REE capability to investigate processes occurring at the interface between different media such as the in depth investigation of REE behaviour is a matter of fact in many geochemical studies. These capabilities are a consequence of the chemical characters of REE that are exploited to investigate processes occurring during migrations of chemical elements in the soil-to-plant system. To carry out this research the Vitis vinifera was the chosen plant since it is one of the most important botanic species exploited for alimentary purposes. During this research, changes of REE behaviour in the soil-Vitis vinifera system was assessed on specimens growing off-soil and on-soil conditions in order to evaluate if this behaviour is influenced by a plant effect in terms of elemental fractionations along the REE series. These studies have been obtained studying REE distributions in bioavailable and pseudo-total soil fractions and comparing them with REE contents in different plant portions during different growth stages. Changes in REE features induced by the different soil characters have been assessed producing the growth of Vitis vinifera specimens onto different soils and also grafted onto different rootstocks usually exploited in Sicily. All these experiments have been carried out under controlled lab conditions. All the indications provided by these experiments have been considered as preliminary basis to investigate the REE behaviour of Vitis vinifera specimens growing in-field onto different soils. The complicated Sicilian geology allowed us to recognise plants growing on very different soils, from metamorphic to eruptive and sedimentary parent rocks that gave us a comprehensive scenario of relationships occurring between REE in the bioavailable soil fractions and in the related vine berries. The results indicate that REE fractionations in off-soil growing plants are negligible whereas REE distributions in plant organs of vine growth on-soil mainly depend on the composition of bioavailable soil fraction. Detailed recognitions of REE distributions in these plants confirmed that REE in Vitis vinifera behave according to two main mechanisms: REE scavenging in roots and REE complexation in aerial parts. In particular, roots are the plant organs where REE are preferentially concentrated, in particular elements from Sm to Ho (middle REE, MREE) whereas REE complexation through the plant xylem is highlighted by Eu enrichments occurring in aerial plant parts. Eu-positive anomalies suggest that Eu3+ can form stable organic complexes in place of Ca2+ in several biological processes in xylem fluids. The possibility that Eu mobility in these fluids can be enhanced by its reductive speciation as Eu2+ cannot be ruled out. The assessment of the geochemical behaviour of REE according to Tetrad Effect Theory carried out confirms that REE coming from soil are scavenged onto root tissues or mineral surfaces whereas their behaviour in aerial parts of Vitis vinifera is driven by dissolved REE complexation. The results we achieved also suggest that the effective capability of REE to trace the geographical origin of berries is related to the awareness of a detailed soil database where substrata are strictly determined according to their major elements composition and mineralogy.