Tropospheric ozone and cadmium do not have interactive effects on growth, photosynthesis and mineral nutrients of Catalpa ovata seedlings in the urban areas of Northeast China

Abstract Heavy metal contamination and tropospheric ozone (O3) pollution often co-occur in heavy industrial urban areas, adversely affecting urban plant health. Little is known about the characteristics of growth, physiological metabolism, bioaccumulation of cadmium (Cd) and mineral nutrients in urban trees under the combination of soil Cd contamination and elevated O3 exposure. In this study, one-year-old street tree Catalpa ovata G. Don seedlings were exposed to Cd contaminated soil (0, 100, 500 mg/kg soil) with 40 µg/m3 O3 (ambient air) and 120 µg/m3 O3 (elevated O3 exposure) for 4 weeks. The results revealed that 500 mg/kg soil Cd addition alone decreased net photosynthetic rate, stomatal conductance, peroxidase activity and increased abscisic acid content and oxidative injury in the leaves of C. ovata. Furthermore, Cd soil contamination decreased leaf, stem, root and total biomass and affected Cd, Mg, Fe, and Zn contents in leaves (P 0.05). Our findings suggest that C. ovata is an appropriate tree species for urban greening and afforestation in heavy industrial urban areas with high O3 pollution in Northeast China. To ensure successful afforestation in heavy industrial areas, the long-term and large scale studies are needed to advance our understanding of the combined effects from extreme climate conditions and multi-pollutant exposure on the metabolism of mature urban trees.