Layered nitrogen fertilization regulates root morphology to promote synergistic nitrogen and phosphorus absorption in maize (Zea mays L.)

Context: Maize roots show high morphological plasticity to soil nutrient heterogeneity. However, there are limitations in how to optimize nitrogen (N) fertilization measures to enhance nutrient acquisition capacity by regulating spatial distribution of soil nutrients and root system architecture. Objective: This study aimed to optimize N fertilization measures to regulate root system architecture and enhance nutrient uptake. Methods: The maize (Zea mays L.) trial applied N fertilization at 8 cm (CU8), 16 cm (CU16), 24 cm (CU24) soil depth, and layered N fertilization (CU1-2-1) in a 1:2:1 ratio on the Loess Plateau. Results: The current study indicated the 8 cm N application depth (CU8) stimulates crown root proliferation with 32.7-35.5 % of roots concentrated in the shallow soil layer (0-8 cm); In contrast, deeper fertilization (CU16 and CU24) increased NO3- and available phosphorus (P) concentrations in the 16-32 cm layer by 7.9-73.3 % and 14.3-51.8 % (P < 0.05), respectively, enhancing lateral root length density and surface area by 8.4-17.9 % and 4.6-14.3 % (P < 0.05), and increasing root proportions in the 8-32 cm layer by 0.8-5.4 %; Maize lateral roots exhibited higher root hair length and root phosphatase activity, along with elevated expression levels of N and P transport genes, deep fertilization facilitated synergistic N and P uptake by the root system through promoting lateral root proliferation; Compared with single-layer N fertilization, layered fertilization stimulated both crown and lateral roots, improving yield, N absorption efficiency, and P absorption efficiency by 7.8-24.6 %, 11.1-43.5 %, and 16.8-42.8 % (P < 0.05), respectively, while transitioning root acquisition strategy from "conservative" to "acquisitive.". Conclusions: Layered N fertilization effectively optimized soil nutrient distribution, regulated root morphology, promoted synergistic absorption of N/P, and enhanced crop production potential. Significance: This study revealed the internal mechanism whereby different N-fertilizer placements affect maize yield from a perspective of root morphological traits and physiological functions, providing a solution for improving farmland fertilization for efficient agricultural production.