Nanoscale hydroxyapatite-mediated foliar phosphorus delivery: Phyllosphere interactions and implications for...

There is a need to explore alternative phosphorus (P) delivery strategies to improve P use efficiency for minimizing the related environmental damage and achieving Sustainable Development Goals (SDGs). In this study, foliar application of nanoscale hydroxyapatite (nHAP) exhibited greater potential to promote rice (Oryza sativa L.) growth than NaH₂PO₄ with equivalent P mass under controlled experimental conditions. Specially, the rice shoot and root biomass promotion induced by the application of nHAP at 200 mg/L was 2.1- and 2.4-fold of that by NaH₂PO₄ with equivalent P mass with 200 mg/L nHAP, respectively. Mechanistically, (1) nHAP exhibited greater adhesion and lower rebound on rice leaves than NaH₂PO₄, leading to more effective P supply; (2) nHAP application facilitated the recruitment of phosphate-solubilizing bacteria in phyllosphere. The abundance of Pseudomonas and Bacillus on rice phyllosphere was 203.9 and 12.3% higher than that in control; and (3) metabolomic analyses revealed that nHAP markedly upregulated rice metabolism, particularly in pathways such as inositol phosphate metabolism, the TCA cycle, starch and sucrose metabolism. The content of jasmonic acid and indole acetic acid in rice shoots after foliar application of nHAP was 156 and 11.5% greater than that in NaH₂PO₄ treatment, respectively. Full life-cycle pot experiment, a proof of concept rather than field-scale validation, further indicated that nHAP application was associated with improved yield-related performance and enhanced grain nutritional quality, with starch and protein levels increasing by 56.3% and 24.3%, respectively. These findings suggest that nHAP can potentially serve as an effective alternative of P fertilizer, offering a promising approach for achieving SDG2 (zero hunger).