Phosphorus mediation of cadmium stress in two mangrove seedlings Avicennia marina and Kandelia obovata differing in cadmium accumulation

Mangrove ecosystems are vulnerable to environmental threats. In order to elucidate the effect of phosphorus (P) on cadmium (Cd) tolerance and physiological responses in mangroves under Cd stress, a mangrove specie with salt exclusion Kandelia obovata and a specie with salt secretion Avicennia marina were compared in a hydroponic experiment. The results showed that most Cd was accumulated in mangrove roots and that P addition induced Cd immobilisation in them. Cd stress significantly increased malonaldehyde content whereas P significantly decreased malonaldehyde in mangroves. Phosphorus positively regulated the photosynthetic pigment, proline content and synthesis of non-protein thiols, glutathione and phytochelatins in the leaves under Cd stress conditions. The results suggest different adaptive strategies adopted by two mangroves in a complex environment and A. marina showed a stronger Cd tolerance than K. obovata. The study provides a theoretical basis for P mediated detoxification of Cd in mangrove plants.