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

Methods A pot experiment was conducted using Zea mays L. cv. ZD958 as the experimental material in calcareous soils. Two P fertilizer application ways (uniform and localized application) were set up, and each combined with three types of P fertilizers: monoammonium phosphate (MAP), diammonium phosphate (DAP), and potassium dihydrogen phosphate (KP). Aboveground biomass and P concentration were analyzed, and the main organic P fractions (metabolic P, nucleic acid P, lipid P, and residual P) in the upper, middle, and lower leaves were measured. The root morphological traits (total root length, root surface area, lateral root length and density, etc.) and the 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 demonstrated promotion effect on root morphological traits: increased total root length, 1^st-order lateral root length and density, and root surface area, and on the physiological traits: 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 fractions and their remobilization characteristics from lower to upper leaves remained unchanged. The effects of application way and P fertilizer types on leaf P fractions and their allocation were relatively limited. Partial least squares path modelling analysis showed that the P fertilizer application way and type significantly altered morphological (path coefficients of 0.87 and 0.64, respectively) and physiological traits (path coefficients of 0.80 and 0.49, respectively) of maize roots. Notably, the root morphological and physiological traits exhibit a significant positive correlation with maize aboveground growth (P<0.05), rather than directly affecting leaf P fractions and their allocation.

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