Effects of a heavy metal (cadmium) on the responses of subtropical coastal tree species to drought stress

With global climate change and increased industrialization, drought and heavy metals have become common abiotic stress factors for coastal vegetation. In this study, we investigated the ecophysiological responses of the seedlings of three subtropical coastal tree species ( Barringtonia racemosa , Hibiscus tiliaceus , and Terminalia neotaliala ) to drought stress (D), cadmium addition (Cd), and their combined effects (Cd + D). The results showed that, for all three plant species, treatment D significantly decreased A max , Y(II), qP, and ETR; increased the concentrations of PRO, soluble sugars, ABA, MDA, and O 2 − ; and increased the activity of Rubisco. The concentrations of soluble sugars, MDA, and O 2 − were similar for treatments D and Cd; the only difference was that qP, A max , and ETR values of B. racemosa and the A max value of H. tiliaceus were significantly lower in treatment Cd than in control. The concentrations of PRO, soluble sugars, ABA, and MDA were significantly lower for treatment Cd + D than for treatment D. The O 2 − concentration was positively correlated with the concentrations of soluble sugars and PRO, indicating that osmoregulation was important for the responses of the plants to oxidative stress. ABA was positively correlated with MDA, indicating that ABA was involved in the response to oxidative stress. These results, which show that Cd may weaken the physiological responses of coastal plants to drought stress by increasing ABA accumulation, may provide guidance for coastal ecosystem management in South China.