Abstract
The environmental toxicity of heavy metals in particular cadmium is a public concern. Cadmium is toxic for all living organisms including plants; however, plant species may show different tolerance to the presence of cadmium in their root medium. Adopting practical strategies may reduce cadmium bioavailability or increase the plant tolerance. In the present study, interaction of nitrate was investigated on cadmium treatment in hackberry (Celtis australis L.) seedlings. Different levels of nitrate (0, 50 and 100 mg/L) and cadmium (0 and 5 mg/L) were applied to seedlings via irrigation water during two consequence years. The treatments were arranged in a factorial with completely randomized design in four replications. The results of ANOVA showed that the cadmium-nitrate interaction was significant on leaf Cd concentration and root dry weight at P = 0.01, and on carotenoids and leaf dry weight at P = 0.05, while it was not significant on the rest of traits. Application of cadmium had no significant effect on new shoot growth, leaf chlorophyll and leaf fresh weight; however, it significantly reduced stomatal water conductance and photosynthesis rate, while it increased leaf transpiration rate, root and stem fresh weights, leaf Cd and proline concentrations. Application of nitrate levels, on the other hand, constantly increased the leaf nitrate concentration, new shoot growth, leaf fresh and dry weights, root fresh weight, stomatal water conductance and photosynthesis rate, whereas it reduced the necrotic points of leaves. The results indicated that the growth characteristics of hackberry seedlings were mainly influenced by nitrate but not cadmium application, and this ornamental tree is a tolerant species to high soil Cd levels.
Highlights
Heavy metals have been a component of our environment in a balanced level without significant problem; human activities toward modern life and industrialization have increased the heavy metal distribution and bioavailability (Lamastra et al, 2018; Vyslouzilova et al, 2003)
Industrial wastes and wastewater application, metalliferous mining and smelting, energy and fuel production, vehicle emissions and agricultural fertilizer applications are among the most important human activities leading to enhanced heavy metal pollution of our environment (Khan et al, 2018; Souri et al, 2018)
The results of ANOVA (Table 1) showed that the interaction of cadmium-nitrate on root dry weight and leaf Cd concentration was significant at P 1⁄4 0.01, and on leaf dry weight and leaf carotenoid concentration was significant at P 1⁄4 0.05, and their interaction on the rest of traits was not significant
Summary
Heavy metals have been a component of our environment in a balanced level without significant problem; human activities toward modern life and industrialization have increased the heavy metal distribution and bioavailability (Lamastra et al, 2018; Vyslouzilova et al, 2003). Industrial wastes and wastewater application, metalliferous mining and smelting, energy and fuel production, vehicle emissions and agricultural fertilizer applications are among the most important human activities leading to enhanced heavy metal pollution of our environment (Khan et al, 2018; Souri et al, 2018). Ornamentals (in nursery or in landscape plantations) can be used in urban areas, and to be irrigated with refined wastewater containing degrees of heavy metals without significant problem (Wang et al, 2012; Hatamian et al, 2018). Many perennial species woody trees are good biomonitor of heavy metals (Yang et al, 2018). Significant differences in the uptake of metals have been observed in willow varieties and clones (Yang et al, 2018; Vyslouzilova et al, 2003)
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