This study aimed to investigate the impact of post-anthesis heat stress on yield formation and nitrogen assimilation capacity in wheat genotypes differing in heat tolerance, so as to provide a theoretical foundation for resilient and stable-yielding cultivation strategies.

Field experiments were conducted from 2022 to 2024 at the National High-Tech Agricultural Park of Anhui Agricultural University using a split-plot design. Temperature was set as the main factor with two levels, including high temperature stress (HT) and ambient control (CK), while three nitrogen rates (no nitrogen (N0), 112.5 kg·hm^-2 (N1), and 225.0 kg·hm^-2 (N2)) and six wheat cultivars (three heat-tolerant: HM33, LK1109, AN1589; three heat-sensitive: FM5, TN19, WK1702) were arranged as subplot factors. High temperature stress was applied after anthesis. Grain yield, photosynthetic parameters (LI-6800), and activities of key nitrogen metabolism enzymes (spectrophotometry) were determined.

High-temperature stress after anthesis significantly inhibited wheat growth, development, and physiological metabolism, leading to a marked decrease in yield, dry matter weight, relative chlorophyll content (SPAD), leaf area index (LAI), net photosynthetic rate (P_n), stomatal conductance (G_s), transpiration rate (T_r), nitrate reductase (NR) activity, and glutamine synthetase (GS) activity, as well as nitrogen accumulation, nitrogen use efficiency, nitrogen absorption efficiency, and nitrogen fertilizer use efficiency. The yield reduction due to high-temperature stress exhibited significant varietal heat tolerance differences and nitrogen application effects: the two-year average yield reduction of heat-tolerant varieties of HM33, LK1109, and AN1589 under N0, N1, and N2 treatments were 9.71%-6.13%, 9.91%-6.24%, and 11.87%-6.42%, respectively, lower than the reductions in sensitive varieties of FM5, TN19, and WK1702, which were 15.26%-10.38%, 12.56%-9.84%, and 12.93%-11.17%, respectively. In terms of physiological mechanisms, high-temperature stress after anthesis significantly reduced P_n across all nitrogen treatments, with the reduction showing a decreasing gradient as nitrogen levels increased: N0>N1>N2. The changes in G_s and T_r followed the same pattern as P_n. Furthermore, high-temperature stress significantly reduced NR and GS activity in the flag leaves across all nitrogen treatments, but increased nitrogen fertilization effectively and alleviated the decline in enzyme activity, with the highest enzyme activity observed under the N2 treatment. The reduction in nitrogen use efficiency under high-temperature stress also showed varietal differences: the nitrogen use efficiency of the heat-tolerant variety HM33 decreased the least under the N2 treatment (by 20.00%), while the sensitive variety FM5 exhibited the greatest decrease (31.55%) under the same treatment.

Post-flowering high temperature stress significantly reduced wheat yield, while the application of nitrogen fertilizers (112.5 and 225.0 kg·hm^-2) effectively mitigated this decline. Heat-tolerant varieties minimized yield losses by maintaining the activity of key nitrogen-metabolizing enzymes and optimizing nitrogen assimilation and transport. Increased nitrogen application, particularly at the 225.0 kg·hm^-2, significantly enhanced nitrogen use efficiency and promoted the accumulation of assimilates in grains. These results demonstrated that combining heat-tolerant genotypes with appropriate nitrogen management could improve thermotolerance in wheat, which provided a theoretical foundation for cultivating high and stable yields under heat stress.

Under the background of global warming, this paper explored the physiological mechanism of anthocyanin content in colored wheat in response to high temperature stress in the middle of grain filling, so as to lay a theoretical basis for further coping with the high-quality cultivation of functional colored wheat varieties under climate warming.

The experiment was conducted in Hefei High-tech Agricultural Park in the 2022-2023 and 2023-2024 growing seasons. Six colored wheat varieties with different colors were selected and subjected to high temperature stress treatment (T) for 5 days at the middle stage of filling, with the same materials grown under ambient temperature as the controls (CK).

Under high temperature stress after anthesis, the net photosynthetic rate, stomatal conductance, transpiration rate, relative chlorophyll content (SPAD), dry matter partition, soluble sugar content, sucrose synthase activity, anthocyanin content, anthocyanidin synthase activity, chalcone synthase activity and phenylalanine ammonia-lyase activity of colored wheat were significantly reduced, and the yield of six varieties of colored wheat decreased by 9.10% to 16.94%, 1000-grain weight decreased by 7.84% to 16.94%, and anthocyanin content decreased by 7.18% to 14.17%. The yield, photosynthetic intensity, SPAD value, dry matter partition, soluble sugar content, sucrose synthase activity, anthocyanin content, anthocyanidin synthase activity, chalcone synthase activity, and phenylalanine ammonia-lyase activity of different varieties of colored wheat were: Qinbai 1>Qinlü 3>Qinzi 1>Xinchun 36>Qinhe 2>Qinlan 1, and the anthocyanin content was: Qinhei 2>Xinchun 36>Qinzi 1>Qinlü 3>Qinlan 1>Qinbai 1. The yield of heat-resistant wheat varieties of Qinbai 1, Qinlü 3 and Qinzi 1 decreased significantly less than that of heat-sensitive wheat varieties Qinhei 2, Xinchun 36 and Qinlan 1. The decreases in photosynthetic intensity, SPAD value, dry matter fraction, soluble sugar content, sucrose synthase activity, anthocyanin content, anthocyanidin synthase activity, chalcone synthase activity and phenylalanine ammonia-lyase activity of color wheat varieties Qinhei 2, Xinchun 36 and Qinzi 1 with high anthocyanin content were smaller than those of Qinlü 3, Qinlan 1 and Qinbai 1 with low anthocyanin content. Correlation analysis showed that the yield of each color wheat variety was significantly positively correlated with 1000-grain weight, sucrose content, sucrose synthase activity, flag leaf net photosynthetic rate, stomatal conductance, transpiration rate and SPAD value, anthocyanin content was significantly positively correlated with soluble sugar content, and yield was negatively correlated with anthocyanins, but the correlation was not significant. After high temperature stress after anthesis, the decomposition of sucrose bound to free anthocyanins decreased, and the decomposition of anthocyanins in grains increased, which supplemented the growth and development of wheat.

The antioxidant activity of anthocyanins helped crops resist external stress, and the decline of various indexes of color wheat varieties with higher anthocyanin content was comparable to that of color wheat varieties with lower anthocyanin content under high temperature stress after anthesis, the anthocyanin content was significantly positively correlated with soluble sugar content. In conclusion, the accumulation of anthocyanin content could respond to high temperature stress, reduce the decrease of soluble sugar content, and increase the heat resistance of colored wheat.