The effects of increasing concentration of Cd in nutrient solution on growth, mineral uptake and phytotoxicity symptoms in Eucalyptus maculata and E. urophylla seedlings were studied under greenhouse conditions. Seedlings were kept for five weeks in 2 L pots containing Clark's nutrient solution amended with 0, 45, 90, 135 and 180 muM as CdSO4. After one week of exposure to Cd treatments seedlings of E. maculata exhibited nerval reddish spots, interveinal leaf chlorosis, leaf necrosis, drought and root darkening, whereas E. urophylla showed additionally apical dieback and leaf fall. The critical dose to reduce shoot dry matter by 10% was low; 2.4 muM and 1.5 muM of Cd to E. maculata and E. urophylla, respectively, while toxicity critical concentration in the shoots were 14.5 and 10.8 mg kg-1 dry matter for these species, respectively.These results indicate that E. maculata is probably less sensitive to Cd than E. urophylla. It was also found that Cd reduced translocation of Cu by 24 and 43% as compared to control in E. maculata and E. urophylla, whereas translocation of Fe was reduced from 36% on average for the two species in the control to 12% at 180 muM of Cd. Shoot concentrations of Ca and Mg was also reduced in both species, reaching levels below those considered adequate for E. urophylla. Increasing concentration of Cd in nutrient solution reduced Ca and Mg contents in shoots of species, reaching Mg contents below those of the range considered suitable for E. urophylla. Relationships of Cd phytotoxicity in Eucalyptus with Cu and Fe translocation as well as with Mg foliar contents were shown.
Critical toxic levels; eucalypts; forest trees; heavy metals; metal translocation; mineral uptake
