Strip intercropped maize with more light interception during post-silking promotes photosynthesized carbon sequestration in the soil

Photosynthesized carbon assimilation and allocation are crucial for plant responses to environmental changes, such as light. Intercropping typically enhances light interception. However, the effects on photosynthesized carbon allocation and microbial immobilization in intercropping systems remain unclear. We investigated light interception, photosynthetic rate, biomass, grain yield, soil organic carbon (SOC), and performed ¹³CO₂ pulse labeling to trace carbon footprints in the plant-soil system under long-term maize-soybean relay strip intercropping and maize monocropping systems. Results showed that, compared to monocropped maize, intercropped maize exhibited a 15.4 % increase in plant ¹³C fixation and significantly greater belowground carbon allocation, with increases of 52.7 % in roots, 64.1 % in rhizosphere soil, and 81.9 % in bulk soil. These outcomes were attributed to enhancements of 30.2 % in light interception and 16.5 % in photosynthetic rate during the post-silking period. At silking, increased light interception in intercropped maize directly contributed to belowground carbon allocation. During the filling period, the source-sink relationship between limited kernel sink capacity and sufficient source strength regulated belowground carbon allocation, resulting in no significant difference in grain yield between intercropping and monocropping. Additionally, the higher ¹³C content in microbial biomass (by 99.8 %) suggested increased microbial utilization of new carbon, potentially enhancing microbial carbon immobilization under intercropping. After 10 years of cultivation, intercropping resulted in a 13.9 % increase in SOC compared to monocropping. Overall, intercropped maize benefited from enhanced light interception, which facilitated plant carbon fixation and increased photosynthesized carbon sequestration in the soil through improved photosynthesized carbon allocation to the soil and microbial carbon immobilization. These findings demonstrate that strip intercropping cultivation can promote photosynthesized carbon sequestration in soil, thereby enhancing the carbon sink capacity of agroecosystems.