Foliar-Applied Carbon Dots Confer Enhanced Low Phosphorus Tolerance in Sweetpotato Seedling

Improving the utilization efficiency of sweetpotato on soil legacy phosphorus (P) is not only a need for sustainable utilization of P resources, but also an urgent need for cost saving and efficiency enhancement in the sweetpotato industry. Nano carbon dots (CDs), as an exogenous regulatory measure, were sprayed (10 mL, 1.5 mg mL− 1) on sweetpotato seedlings (Shangshu 19 and Xushu 32) grown in low P stress (spraying ultra-pure water as control), after which the root morphological, physiological parameters and rhizosphere properties were analyzed. Foliar-applied CDs promoted the root growth (e.g., increasing root length, projected area, surface area, etc.), and increased the expression of root phosphate transport genes (PHO1, PHT1-4). Meanwhile, foliar-applied CDs significantly reduced the expression level of inositol phosphate of root, and improved phoDgene abundance in Shangshu 19 rhizosphere. For Xushu 32, the expression level of roots citric acid and oxalic acid, and the abundance of rhizosphere pqqCgene increased after spaying CDs. Principal coordinates analysis (PCoA) showed that phoD-harboring Tuwongella, Prosthecobacter, Leptolyngbya, Rubinisphaera, and pqqC-harboring Nitrincola, Novimethylophilus, Ramlibacter, Mycobacterium, Thiomonasplayed key roles on the solubilization of insoluble P in Shangshu 19 and Xushu 32 rhizosphere, respectively. These alterations could increase available P content in Shangshu 19 (53%) and Xushu 32 (67%) rhizosphere, thus increasing the biomass and root P content of sweetpotato seedlings. Foliar-applied CDs would be a promising strategy for sweetpotato to respond low P stress, which provide scientific support for establishing regulation theories and new pathways of efficient P nutrients in sweetpotato cultivation.