Delayed sowing increased dry matter accumulation during stem elongation in winter wheat by improving photosynthetic yield and nitrogen accumulation

Understanding dry matter (DM) accumulation during the stem elongation period (SE) is important for estimating yields. However, the mechanisms underlying SE at different sowing times, and how the main shoots (MS) and tillers contribute to DM accumulation, remain poorly understood. Field experiments were carried out at different sowing times, with two cultivars being grown during two successive growing seasons. The results showed that delayed sowing increased grain yield and DM accumulation after anthesis in MS, but decreased them in the tillers. Different from after anthesis, delayed sowing improved DM accumulation in both MS and tillers during SE. With delayed sowing, the leaf area index (LAI) of MS decreased significantly at jointing but was not significantly altered at booting or anthesis, whereas the LAI of the tillers decreased significantly at all three stages. The specific leaf area of both MS and tillers decreased significantly with a delay of sowing, but radiation use efficiency improved markedly during SE. Delayed sowing dramatically decreased the net loss of DM in non-surviving tillers and led to an increase in nitrogen (N) accumulation during stem elongation, as well as an increase in N productivity. Conversely, delayed sowing reduced the loss of N in non-surviving tillers. In conclusion, the combination of increased photosynthetic yield and N accumulation, together with decreased loss of DM and N, increased the quantity of DM during SE.