The alleviation effect of iron on cadmium phytotoxicity in mangrove A. marina. Alleviation effect of iron on cadmium phytotoxicity in mangrove Avicennia marina (Forsk.) Vierh.

Cd has high activity and bioavailability and is a poisonous element to plants. As a critical ecosysterm, mangroves are subjected to serious Cd pollution. In this research, the hypothesis was presented that improving Fe bioavailability would alleviate Cd phytotoxicity to Avicennia marina (Forsk.) Vierh. To test this, we examined the effect of four exogenous Fe and three Cd concentrations on A. marina. The results showed that a significant positive correlation excited between moderate exogenous Fe concentration and Cd tolerance of A. marina. Moderate exogenous Fe concentration directly or indirectly promoted the formation of Fe plaque, which immobilised more Cd on the root surface and decreased Cd absorption in roots. Furthermore, an exogenous Fe application increased plant biomass and Fe accumulation in A. marina tissues. This improved the competition between Fe and Cd within the plants. Therefore, an Fe application facilitated a decrease in Cd toxicity within A. marina. Simultaneously, a moderate Fe concentration caused an increase in low-molecular-weight organic acid (LMWOA) secretion from the roots. Meanwhile, Cd can be chelated/complexed by LMWOAs. It also played a crucial role in Cd detoxification in A. marina. In conclusion, Fe application accelerated the growth and enhanced Cd tolerance of A. marina. Therefore, improving Fe bioavailability will protect mangroves from Cd contamination.