Interspecific Difference in Foliar Retention and Translocation of Nanoplastics by Typical Salt-Secreting and Salt-Excluding Mangrove Drives Species-Specific Photosynthetic Impairment Mechanisms

Mangroves have become significant sinks for atmospheric nanoplastics (NPs) via foliar capture, posing an urgent ecological threat on their photosynthetic carbon fixation. This study investigated the foliar interactions between negatively charged NPs and two mangroves with contrasting salt-regulation strategies: the salt-secreting <i>Aegiceras corniculatum</i> and the salt-excluding <i>K. candel</i>. The findings indicated that the salt glands in <i>A. corniculatum</i> leaves functioned as NP accumulation hotspots, with a 53.2%-54.1% higher particle density than adjacent epidermal cells. This preferential retention was attributed to the glandular micromorphology and π-π stacking-mediated interfacial adhesion. Critically, salt glands provided entry points for NP internalization in <i>A. corniculatum</i>, allowing rootward translocation at 0.378-0.547 mg kg^-1 d^-1. Conversely, the absence of salt glands in <i>K. candel</i> resulted in complete NP interception by its cuticular layer, restricting internal migration. The differential NP localization patterns further induced species-specific photosynthetic impairment mechanisms. Cuticular NP shielding inhibited the light reaction in <i>K. candel</i> by reducing photon capture efficiency and disrupting electron transport. However, salt gland-facilitated NP internalization triggered dark reaction failure in <i>A. corniculatum</i>, as evidenced by 35.1 to 68.3% downregulation of carbon fixation genes. Our results reveal the role of salt-secreting mangroves as biological concentrators in the global NP cycle and bridge microscale plastic-plant interactions with macroscale carbon-climate feedbacks, redefining mangrove ecosystems as critical nodes in the plastisphere.