The Xiamen Symposium on Marine Environmental Sciences (XMAS 2027)

Arsenic contamination poses an escalating threat to the ecological integrity and ecosystem functioning of mangrove wetlands worldwide. Understanding the biogeochemical mechanisms that govern arsenic mobility, transformation, and sequestration in the rhizosphere is therefore critical for developing effective restoration strategies in impacted coastal systems. Here we synthesize findings from complementary rhizobox and hydroponic experiments on several keystone mangrove species—Aegiceras corniculatum and Avicennia marina etc.—to elucidate the coupled roles of root exudation, iron plaque formation, radial oxygen loss (ROL), and rhizosphere microbiomes in arsenic detoxification.  Our results reveal that mangrove roots create a localized arsenic "sink" at the root–sediment interface through rhizosphere acidification and enhanced secretion of low-molecular-weight organic acids, which together promote arsenic immobilization via adsorption and co-precipitation onto iron plaques. Iron plaque formation exhibits a biphasic response to arsenic stress—stimulated under moderate contamination but diminished under excessive toxicity—while roots retain the vast majority of accumulated arsenic, with translocation factors remaining consistently low, demonstrating strong phytostabilization capacity. Concurrently, arsenic stress selectively enriches As-tolerant bacterial taxa, particularly Proteobacteria and Bacteroidetes, and significantly upregulates key arsenic metabolic genes (arsC, aoxA, arsB, arsM) in the rhizosphere, establishing an active microbial network of arsenic reduction, oxidation, transport, and methylation that complements plant-based detoxification. Iron supplementation further enhances ROL and promotes iron plaque formation, effectively sequestering arsenic and reducing its bioavailability.  Collectively, these findings demonstrate that mangrove species employ a coordinated multi-tiered strategy—combining root morphological plasticity, enhanced ROL, aerenchyma development, iron plaque sequestration, and recruitment of As-metabolizing microorganisms—to mitigate arsenic toxicity. This integrated plant–microbe–iron plaque detoxification framework advances the mechanistic understanding of biogeochemical responses in contaminated coastal wetlands and provides a scientific basis for leveraging nature-based interventions, such as targeted iron amendments and microbiome-assisted phytostabilization, in the ecological restoration of arsenic-impacted mangrove ecosystems.