Analysis of biometric, physiological, and biochemical traits to evaluate the cadmium phytoremediation ability of eucalypt plants under hydroponics

Wastewater reclamation and reuse represent a feasible solution to meet the growing demand for safe water. An environmentally sustainable technology such as phytoremediation is targeted for the reclamation of polluted waters. To this end, the capability of different plant species to tolerate and accumulate pollutants has to be investigated. In this work, eucalypt plants were studied by analysing biometric, physiological, and biochemical parameters related to cadmium (Cd) tolerance and accumulation in two clones (Velino ex 7 and Viglio ex 358) of Eucalyptus camaldulensis Dehnh. x E. globulus subsp. bicostata (Maiden, Blakely & J.Simm.) J.B. Kirkp exposed to 50 mu M CdSO4 under hydroponics for three weeks. The results indicated that both eucalypt clones have a valuable tolerance to cadmium, expressed as the tolerance index (Ti). Biometric investigations showed that, regardless of the clone, the metal exposure affected most parameters related to biomass allocation and leaf growth. On the contrary, significant differences were found between the clones with respect to the chlorophyll content and the Chl a to Chl b ratio. These findings were also confirmed from the analysis of chlorophyll fluorescence transient (OJIP) using the JIP test. Cadmium accumulation occurred in both clones and in particular in the roots, with a poor amount of metal reaching the aerial parts, and the Velino clone showed the highest Cd accumulation. The metal uptake ratio and the phytoextraction efficiency highlight a good Cd phytoremoval ability, especially for the Velino clone. The results are discussed taking into account that, in wastewater phytoremediation systems, root biomass can be completely harvested allowing for the removal of the absorbed metal. Finally, the notable tolerance to submersion and the large environmental adaptability of eucalypt suggest that this plant species represents an inter esting candidate for the phytoremediation of Cd-polluted wastewaters.