Nitrogen response differences at the flowering stage of maize ( Zea mays L.) affect nitrogen use efficiency: a physiological and pathway analysis of nitrogen uptake, photosynthetic characteristics, and carbohydrate synthesis

Abstract BACKGROUND Reducing nitrogen (N) inputs while maintaining crop yield aligns with sustainable development goals. It is therefore important to elucidate the physiological mechanisms underlying maize N use efficiency (NUE). The physiological traits and transcriptional profiles of two maize cultivars, ‘Qiangsheng 101’ (QS) (a low N‐sensitive cultivar) and ‘Zhengdan 958’ (ZD) (a low N‐tolerant cultivar), were analyzed at two N application rates: 150 kg ha −1 (low N, LN) and 300 kg ha −1 (normal N level, NN). RESULTS Compared with LN‐ZD, LN‐QS showed reductions of 11.22% to 14.29% in grain yield (GY), 11.73% to 23.53% in NUE, and 13.11% to 15.97% in radiation use efficiency (RUE). Relative to LN‐ZD, LN‐QS showed a 17.14% to 17.60% reduction in the relative chlorophyll content (SPAD) value and a 14.29% to 19.23% reduction in the net photosynthetic rate (Pn). Soluble sugar content decreased and starch content increased in LN‐QS relative to LN‐ZD ( P < 0.05), whereas no significant differences were observed between NN‐ZD and NN‐QS. Transcriptome analysis revealed downregulation of differentially expressed genes (DEGs) involved in N metabolism, chlorophyll biosynthesis, photosynthesis, and starch and sucrose metabolism in the comparison of LN‐ZD with LN‐QS. Notably, DEGs encoding nitrate reductase (NR) ( Zm00001d039831 ), uroporphyrinogen decarboxylase (UROD) ( Zm00001d028083 ), protochlorophyllide reductase (POR) ( Zm00001d001820 ), and sucrose synthase (SUS) ( Zm00001d029091 ) may be key candidate genes responsible for the low efficiency of LN‐QS. CONCLUSION Under low N conditions, the reduction in N uptake and metabolic capacity in QS led to diminished photosynthetic performance, which subsequently constrained carbon assimilation, ultimately reducing NUE and GY, while ZD remained stable. These results provide valuable insights for the optimization of N management strategies and the improvement of maize productivity. © 2026 Society of Chemical Industry.