Differential regulation of root iron plaque formation in a mangrove species, Kandelia obovata by biodegradable and conventional nanoplastics: Evidence from interfacial interactions, microbial communities, and redox conditions

Nanoplastics (NPs) increasingly infiltrate mangrove ecosystems, yet their impact on the formation and stability of iron plaque (IP), a key root interface, in mangrove species remains unclear. This study systematically investigated the effects of two types of NPs, biodegradable polylactic acid (PLA) and conventional polystyrene (PS), on IP formation in the roots of Kandelia obovata using potted experiments simulating tidal conditions. Results showed that PLA increased IP content by 105.63 %, while PS reduced it by 37.45 %. Both NPs inhibited the crystallization of iron minerals within IP, with PS showing a stronger inhibitory effect. Mechanistically, PLA promoted IP formation directly through the release of lactic acid that chelated Fe(III), and indirectly by increasing Fe-oxidizing bacteria (FeOB) and bioavailable Fe(II). In contrast, PS disrupted IP stability through electrostatic and hydrogen bonding interactions, while indirectly inhibiting IP formation by suppressing reactive oxygen species (ROS) and altering Fe-reducing bacteria (FeRB) abundance. This study is the first to comprehensively assess the contrasting effects of biodegradable and conventional NPs on IP formation on mangrove root surfaces, offering new insights into their ecological behavior at the plant-sediment interface. It provides fresh perspectives on the impact of NPs on waste and pollutant removal in plant-based environmental remediation technologies.