Elevated soil temperature alters nitrogen uptake, allocation and utilization in maize during the late vegetative stage

As global temperatures rise, soil warming is emerging as a critical factor influencing maize productivity. However, the impacts on root function and nitrogen utilization remain insufficiently understood. To investigate these effects, a pot experiment was conducted in an environment-controlled greenhouse during the late vegetative stage under three soil temperature regimes: 28 °C, 33 °C, and 38 °C. 15 N-labeled urea was applied to trace nitrogen dynamics. Results showed that elevated soil temperature markedly altered root morphology and microstructure. Root length and surface area decreased, while cortical lacunae proportion increased significantly, particularly at 38 °C. These structural changes were accompanied by lower root activity, reduced stomatal conductance and transpiration, and a 46.97–60.44% decrease in 15 N uptake rate. The decline in nitrogen uptake rate reduced total nitrogen content in vegetative organs, whereas nitrogen content in grain remained relatively stable, indicating enhanced internal nitrogen remobilization. However, under 38 °C, this compensatory effect was not sufficient to prevent accelerated leaf senescence, which caused a 3.96% reduction in kernel weight, and a 34.52% decline in grain yield. Overall, these results showed that soil warming disrupted nitrogen uptake, allocation, and utilization in maize, and that 38 °C soil warming exceeded the capacity of the plant to maintain coordinated nitrogen supply during grain filling. These findings provide a physiological basis for developing management strategies to mitigate the adverse effects of soil warming on maize productivity.