Stable foliar colonization of nanocoated nitrogen-fixing bacteria enhances crop nitrogen supply

Biological nitrogen fixation through foliar application of nitrogen-fixing bacteria presents a promising route to reduce reliance on synthetic fertilizers but remains limited by challenges in bacterial adhesion and survival in the phyllosphere. We developed a nanocoated inoculant encapsulating Klebsiella variicola W12 using metal-phenolic networks and sodium alginate for enhanced nitrogen fixation under nitrogen-depleted conditions. The nanocoating improved bacterial resistance to UV radiation, oxidative stress, aerobic conditions and desiccation, enhancing adhesion and biofilm formation on leaf surfaces. Colonization increased 3.3-fold compared to non-coated bacteria at 14 days after application, improving epiphytic and endophytic persistence. The nanocoated bacteria contributed 27.89% of total plant nitrogen, over twice that of non-coated bacteria, resulting in a 1.4-fold increase in rice fresh weight after 54 days. Field trials demonstrated potential savings of chemical fertilizer of 74.38 kg N ha^-1, highlighting a sustainable and effective strategy to improve crop productivity with reduced reliance on chemical nitrogen fertilizers and environmental impacts.