Global warming has increased the occurrence of high temperature stress in plants, including maize, resulting in decreased the grain number and yield. Previous studies indicate that heat stress mainly damages the pollen grains and thus lowered maize grain number. Other field studies have shown that heat stress after pollination results in kernel abortion. However, the mechanism by which high temperature affect grain abortion following pollination remains unclear. Hence, this study investigated the field grown heat-resistant maize variety “Zhengdan 958” (ZD958) and heat-sensitive variety “Xianyu 335” (XY335) under a seven-day heat stress treatment (HT) after pollination. Under HT, the grain numbers of XY335 and ZD958 were reduced by 10.9% (p = 0.006) and 5.3% (p = 0.129), respectively. The RNA sequencing analysis showed a higher number of differentially expressed genes (DEGs) between HT and the control in XY335 compared to ZD958. Ribulose diphosphate carboxylase (RuBPCase) genes were downregulated by heat stress, and RuBPCase activity was significantly lowered by 14.1% (p = 0.020) in XY335 and 5.3% (p = 0.436) in ZD958 in comparison to CK. The soluble sugar and starch contents in the grains of XY335 were obviously reduced by 26.1 and 58.5%, respectively, with no distinct change observed in ZD958. Heat stress also inhibited the synthesis of grain starch, as shown by the low activities of metabolism-related enzymes. Under HT, the expression of trehalose metabolism genes in XY335 were upregulated, and these genes may be involved in kernel abortion at high temperature. In conclusion, this study revealed that post-pollination heat stress in maize mainly resulted in reduced carbohydrate availability for grain development, though the heat-resistant ZD958 was nevertheless able to maintain growth.

Enhancing maize lodging resistance with plant growth retardants (PGRs) is common in maize production. However, the underlying mechanisms of yield formation as affected by PGRs are still poorly understood. A field experiment contained PGR application (a mixture of ethephon and cycocel, EC) with normal (T1) and double (T2) doses and water control (CK) was conducted at four maize plant densities (4.5, 6.0, 7.5, and 9.0 plants m⁻²) in 2020 and 2021. In this two-year study, the grain yield and kernel number per ear (KNE) of EC treatments were reduced by 4.8–9.0% and 3.3–12.2%, respectively, compared with CK under densities of 4.5, 6.0, and 7.5 plants m⁻² without lodging. However, under the density of 9.0 plants m⁻², EC treatments had no pronounced effects on grain yield and yield components. Across all densities, EC significantly decreased the leaf area index (LAI), and the lowest LAI was recorded in T2. The concentrations of nonstructural carbohydrates (NSCs; starch and soluble sugar) in the stem were significantly decreased by 9.9–10.2% in T2 averaged all densities. The sucrose and starch concentrations in grains also declined in the EC treatments. The key enzymes (cell wall acid invertase, sucrose synthase, and adenosine diphosphate pyrophosphorylase) and grain polyamine concentrations showed a slight downward trend under EC treatments compared to CK. NSCs in stems and grains, kernel enzyme activities, and polyamines in grains presented significant positive correlations with KNE. Additionally, structural carbohydrate (SC; including cellulose, hemicellulose, and lignin) concentrations in stems were improved with enhanced lodging resistance by spraying EC. Significant negative relationships were observed between SC with kernel number m^-2 (KNM) and yield, suggesting that improved SC in stems might affect the availability of NSCs for kernel set. Although the lowest kernel weight and KNE were obtained at 9.0 plant m⁻², relatively high LAI still ensured high KNM and high yield. Collectively, EC treatment increased SC in stems, enhanced lodging resistance of maize and reduced NSC availability for kernels, ultimately presenting adverse effects on maize kernel number and yield under relative low density.

Against the background of long-term climate change, quantifying the response of maize growth and development to climate change during critical growth stages will contribute to future decision-making in maize production. However, there have been few reports on the impact of climate change on maize dry matter accumulation and yield formation using long-term field trial data. In this study, field trial data from 13 agricultural meteorological stations in the Beijing–Tianjin–Hebei region from 1981 to 2017 were analyzed using partial correlation analysis and multiple regression models to investigate the effects of climate change on maize growth and yield. The results showed that the average temperature (Tavg) and accumulated effective precipitation (EP) during the maize growing season increased while the accumulated solar radiation (SRD) decreased from 1981 to 2017. During the seedling stage (GS1, VE-V8) and ear development stage (GS2, V8-R1), Tavg increased by 0.34 °C and 0.36 °C/decade, respectively, and EP increased by 1.83 mm and 3.35 mm/decade, respectively. The significant increase in Tavg during GS1 was the main reason for the inhibitory effect of climate change on maize growth, development, and biomass accumulation. However, the increase in SRD during the grain formation stage (GS3, R1–R3) and grain filling stage (GS4, R3–R6) was favorable for yield formation, increasing the grain number per ear (GN) and grain weight (GW) by 5.00% and 2.84%, respectively. SRD significantly increased after the silk stage, partially offsetting the adverse effects of temperature on maize yield formation, but the final result was a 0.18% and 0.94% reduction in maize plant dry weight (TDW) and grain yield (GY), respectively, due to the combined effects of the three climate factors. Spatially, climate change mainly had a negative impact on maize in the eastern and western parts of the central region of Beijing–Tianjin–Hebei, with a maximum GY reduction of up to 34.06%. The results of this study can provide a scientific basis for future decision-making in maize production against the background of climate change.

Phased warming in late winter and early spring can increase winter wheat grain yield. However, the effects of different durations of warming during this period on winter wheat grain yield and quality are not yet clear. Therefore, this study conducted field warming experiments in a movable polyethylene greenhouse during the late winter and early spring stages of the three wheat growing seasons from 2019 to 2022. The results showed that the accumulated growing degree days (GDD) of the warming treatment during the warming period were increased by 87.3–215.7 °C d compared to the control (CK). The warming treatment advanced and prolonged the duration of vegetative growth and spike differentiation after regreening, promoted spike and flower development, and increased grain length, grain width, and grain area. During the three growing seasons, the longer the warming duration (WD) of the warming treatment, the more obvious were the observed promoting effects on the kernel number per spike and 1000-kernel weight. From 2019 to 2021, compared to the CK, the spike number per unit area and grain yield of the warming treatments increased with the prolongation of WD. However, in the 2022 growing season the spike number per unit area and grain yield of the warming treatment were increased with longer WD, reaching the maximum at WD of 56 days and then gradually decreasing with longer WD. Compared to CK, the grain protein content, wet gluten content, and sedimentation value of the warming treatment decreased with the prolongation of WD. The promotion effect of longer WD on grain starch content and protein yield was more significant. In summary, the accumulated GDD during the warming period compared to CK was 155.8–181.2 °C d, and at WD of 50–56 days a relatively higher grain yield and protein yield could be obtained.