Objectives The response of photosynthetic characteristics and yield formation of winter wheat at different yield levels to nitrogen form of fertilizers was investigated, to provide a theoretical basis for fully utilizing of the production potential of wheat fields in the Huang-Huai-Hai region, Northern China.

Methods A winter wheat field experiment was conducted in Qihe County, Dezhou City, Shandong Province, a typical fluvo-aquic soil region. A high wheat yield field (annual yield level 9000 kg/hm, denoted as H) and a medium-low yield field (with an average yield of 6750 kg/hm, denoted as L) were selected as the main plots, and three types of nitrogen fertilizers as subplots, namely N1 (calcium nitrate, 26% N), N2 (ammonium chloride, 17% N), and N3 (urea, 46% N), constituting a total of six treatments. At 0, 7, 14, 21, 28, and 35 days after anthesis, the canopy photosynthetically active radiation (PAR), leaf area index (LAI), chlorophyll content, and chlorophyll fluorescence parameters of wheat were measured; the sucrose content and sucrose phosphate synthase (SPS) activity in flag leaves were determined; and the grain weight was recorded to calculate the grain-filling rate. At maturity, the yield, as well as the spikelet number per spike and 1000-grain weight, was determined.

Results Under the same yield-level, the N3 treatment significantly increased the leaf area index (LAI) and PAR compared with N1 and N2. Furthermore, at 14, 21, and 28 days after anthesis, N3 exhibited significantly higher relative chlorophyll content, chlorophyll fluorescence parameters, sucrose content, and sucrose phosphate synthase (SPS) activity in flag leaves. Consequently, N3 achieved the highest average grain-filling rate, resulting in the greatest 1000-grain weight and grain yield, which were 6.32%–21.1% and 5.57%–51.78% higher than those under N1 and N2, respectively. Under identical nitrogen fertilizer conditions, all indicators in high-yield wheat fields outperformed those in medium- and low-yield fields.

Conclusions Regardless of yield potential, amide-type nitrogen fertilization outperformed nitrate and ammonium forms in establishing an optimal population structure. It demonstrated a superior capacity to enhance the flag leaf area index and photosynthetically active radiation interception efficiency. Consequently, this led to a marked increase in post-anthesis sucrose synthesis and translocation, driving higher grain-filling rates, 1000-grain weight, and final grain yield. Thus, amide-type nitrogen is established as the predominant nitrogen form for maximizing winter wheat yields in the Huang-Huai-Hai.