Objectives Considering the heterogeneous spatial distribution of soil nutrients, this study simulated uneven phosphorus (P) availability through localized P fertilizer application to investigate the mechanisms underlying efficient P acquisition by maize roots during root-soil interaction process. We further systematically examined the response of high P use efficiency in relation to changes in leaf P fractions and their allocation patterns. This study provides a theoretical basis for rational P fertilizer application and sustainable P resource utilization in maize production.

Methods A pot experiment was conducted using Zea mays L. cv. ZD958 grown in calcareous soils. Two P fertilizer application strategies (uniform and localized application) were set up, each combined with three P fertilizer types: monoammonium phosphate (MAP), diammonium phosphate (DAP), and potassium dihydrogen phosphate (KP). Aboveground biomass and P concentration were analyzed, and the major organic P fractions (metabolic P, nucleic acid P, lipid P, and residual P) in the upper, middle, and lower leaves were measured. Root morphological traits (total root length, root surface area, lateral root length and density, etc.) and physiological traits (rhizosphere pH, carboxylate concentration, and acid phosphatase activity) were also assessed.

Results Compared to uniform P fertilizer application, localized P fertilizer application significantly increased maize shoot biomass by 20.0% and P accumulation by 39.1%, with DAP exhibiting the highest beneficial effect. Localized P application markedly promoted root morphological development, as indicated by increased total root length, 1^st-order lateral root length and density, and root surface area. It also enhanced root physiological activtity, characterized by intensified rhizosphere acidification, increased carboxylate concentration and acid phosphatase activity. Localized P application increased metabolic P concentrations in middle and lower leaves and nucleic acid P concentrations in upper leaves, while other leaf P fractions and their remobilization from lower to upper leaves remained unchanged. The effects of P application strategy and fertilizer type on leaf P fractions and their allocation were relatively limited. Partial least squares path modelling analysis showed that P fertilizer application strategy and fertilizer type significantly altered root morphological (path coefficients of 0.87 and −0.64, respectively) and physiological traits (path coefficients of 0.80 and −0.49, respectively). Notably, these root morphological and physiological traits were significantly positively correlated with maize aboveground growth (P<0.05), rather than exerting direct effects on leaf P fractions and their allocation.

Conclusions In calcareous soils, localized P application effectively enhances the P utilization capacity of maize primarily by promoting root elongation, increasing lateral root density and the proportion of fine roots, lowering rhizosphere soil pH, and boosting organic acid secretion and acid phosphatase activity, rather than through influencing the composition and redistribution of P in maize leaves. These findings highlight the central role of root-soil interactions in improving P utilization efficiency in maize.