Effects of sowing date on the utilization efficiency of light and temperature resources and yield in Brassica napus in the middle reaches of the Yangtze River

Delaying the sowing date of winter rapeseed can help alleviate the cropping conflict between rice and rapeseed in the Middle Yangtze River region; However, late sowing significantly reduce yield. To investigate the mechanisms underlying yield reduction associated with early and late sowing and to explore strategies for improving yield, a three-year field experiment was conducted from 2018 to 2021 with three sowing dates: early sowing (S1, September 20), optimal sowing (S2, October 1), and late sowing (S3, October 10). This study systematically analyzed yield performance, light and temperature resource use efficiency, and physiological responses related to carbon metabolism. The results showed that: (1) S2 improved the utilization efficiency of light and temperature resources, leading to higher yield and oil production. (2) Compared with S1, S2 exhibited a shorter growth period and a gradual reduction in effective accumulated temperature, yet significantly enhanced the efficiency of light and temperature resource use. Compared with both S1 and S3, S2 also showed higher activities of key carbon metabolism enzymes in leaves (Rubisco, fructose-1,6-bisphosphatase, and sucrose synthase), which promoted soluble sugar accumulation. (3) At the flowering stage, S2 had a higher canopy light interception rate and single-leaf photosynthetic capacity than S1 and S3, along with significantly increased soluble sugar and amino acid contents in bleeding sap, facilitating the efficient transport of photosynthates to siliques. In conclusion, sowing rapeseed at an optimal date enables more efficient use of light and temperature resources, improves accumulated temperature productivity and light energy utilization, and synergistically enhances both yield and seed quality. Insufficient utilization of light and temperature resources is a major limiting factor for yield in late-sown rapeseed, and these findings provide theoretical and practical guidance for variety selection and cultivation strategies under late sowing conditions.