Belowground and aboveground interactions are important in increasing yield and nutrient-use efficiency in intercropping. However, how the yield and P-use efficiency respond to shoot-root interactions in intercropping remains unknown. Maize in mono- and intercropping was grown under field conditions (regosol soil, initial Olsen-P 12.6 mg kg−1) with P supply of 0 and 35 kg P ha yr-1 (P0 and P35, respectively) for 3 years. Compared with monocropping, intercropping significantly increased grain yield (by 13.9 %) and plant P-use efficiency (45.1 %), which might be attributed to increasing light interception during the post-silking period. Both sufficient P supply (P35 treatment) and increased light interception delayed leaf senescence through minimizing the degradation of chlorophyll and remobilisation of P as well as increasing the expression of ZmSee2β gene that influences leaf longevity. Increased light interception associated with enhanced leaf longevity increased the duration of photosynthesis, which provided assimilates not only for achieving yield potential, but also for maintaining root growth. It is suggested that sucrose translocated to roots serves as a substrate for root growth and improves P uptake to satisfy the nutrient demand of expanding shoots. This work contributed to understanding of the resource-use efficiency in intercropping as regulated by shoot-root interactions.