Objectives To address the problem of excessive phosphorus fertilizer input and low utilization efficiency in winter wheat production on the Loess Plateaus, this study explored the effects of phosphate fertilizer reduction on improving phosphorus utilization efficiency in wheat aiming to provide a theoretical basis and practical guidance for fertilizer reduction and efficiency enhancement in the Loess Plateau.

Methods This study was conducted based on a long-term quantitative fertilizer reduction experiment for winter wheat in southern Shanxi, China. A rhizobox experiments was performed to investigate the effects of farmer conventional fertilization (HP), optimized fertilization (MP), and optimized fertilization without phosphorus application (LP) on wheat root morphology, plant phosphorus content and phosphatase activity in roots and rhizosphere soil. The mechanisms underlying the effects of phosphorus fertilizer reduction on rhizosphere soil phosphorus transformation and wheat phosphorus uptake were further explored.

Results Compared with the HP treatment, wheat plant height significantly increase under LP and MP treatments, while chlorophyll content increased by 14% and 16%, respectively. The LP treatment exhibited the greatest root length (137.62 cm) and phosphatase activity (0.62 U/g). Due to long-term difference in phosphorus application rates, soil available phosphorus (AP) varied among treatments, resulting in significant differences in total phosphorus and inorganic phosphorus content in roots (P<0.05), with the HP treatment exhibiting significantly higher than the MP and LP treatments. In the rhizosphere soil, acid phosphatase activity (ACP) and alkaline phosphatase activity (ALP) under the HP treatment were 15.88 and 53.68 nmol/(g·h), respectively, both significantly lower than those under the MP and LP treatments. Specifically, ACP activity under the MP and LP treatments was 1.45 and 1.57 times that under the HP treatment, respectively; while ALP activity was 1.35 and 1.34 times that under HP treatment. In the bulk soil, microbial biomass phosphorus (MBP) content under HP and MP treatments was significantly higher than under LP treatment, being 1.62 and 1.38 times greater, respectively. In contrast, soil MBP content showed no significant differences among the three treatments in the rhizosphere soil (P>0.05). Correlation analysis revealed that total phosphorus and inorganic phosphorus content in roots of wheat showed highly significant positive correlations with soil AP content (P<0.01); while root phosphatase activity, rhizosphere soil ACP and ALP activity exhibited significant negative correlations with AP content (P<0.01). Moreover, whether in rhizosphere or bulk soil, soil organic carbon and total nitrogen content showed significant negative correlations with AP content, while exhibiting positive correlations with root phosphatase activity, soil ACP and ALP activity (P<0.05). In the rhizosphere soil, soil pH showed a highly positive correlation with AP content, and an extremely significant negative correlation with root phosphatase activity, soil ACP and ALP activity (P< 0.001).

Conclusions Under the optimized fertilization (MP and LP) treatments, wheat optimizes root morphology enhances root phosphatase activity, and synergistically increases soil phosphatase activity. These responses improve the rhizosphere microenvironment, ultimately promoting wheat growth and phosphorus uptake.