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In recent years, the frequency and intensity of exposure to heat stress have increased gradually, seriously hampering the production of maize. This paper presents a study designed to analyze how the development, physiology and dispersal of pollen from the heat‐resistant maize variety Zhengdan958 and the heat‐sensitive maize variety Xianyu335 are affected by exposure to heat stress during the tasselling stage. Our results showed That exposure to heat stress significantly increased the antioxidant enzyme activity in pollen. Upon visual inspection of the pollen, we found that the lower water content had given rise to wrinkles in the pollen surface, sunken germination pores, and morphological deformations. In addition, the anther dehiscence process was hindered, resulting in a reduced amount of pollen being dispersed. We also found elevated levels of abscisic acid (ABA), jasmonic acid (JA) and its derivatives, indole acetic acid (IAA) and gibberellin‐3 (GA3) in heat‐pollens, as well as elevated ratios of IAA to ABA and ABA to GA3. Ultimately impaired pollen fertility. Summarizing, our experiment revealed that reduced pollen quantity and quality are significant contributors to fertility losses in summer maize exposed to heat stress at anthesis, and we hope that our analysis of the physiological mechanisms involved can contribute to the development of crop management measures aimed at countering the increasingly detrimental effects of heat stress on the production of summer maize. [ABSTRACT FROM AUTHOR]

The greenhouse effect caused by global warming was becoming more and more obvious, resulting in increased frequency of high temperature and high humidity, which significantly affected maize productivity. However, it was poorly understood how the interactions of high temperature and high humidity affected leaf senescence, photosynthetic performance and yield of summer maize. Three stress treatments including (a) high temperature stress (T), (b) waterlogging stress (W) and (c) complex stress (T‐W) were set at the third leaf stage (V3), the sixth leaf stage (V6) and the tasselling stage (VT) in 2019–2020 to explore the influence mechanism of complex stress. Each stress treatment period lasted 6 days. Non‐stressed plants served as control. Yield, antioxidant enzyme activity, photosynthetic characteristics, and dry matter accumulation were determined. Our study found that the activity of antioxidant enzymes was significantly decreased, while malonyldialdehyde (MDA) accumulation was increased under each stress treatment. As a result, the photosynthetic characteristics were impaired, manifested in a significant decrease in net photosynthetic rate (Pn), enzyme activities of phosphoenolpyruvate carboxylase (PEPCase) and ribulose diphosphate carboxylase (RUBPCase). The decrease in photosynthetic intensity affected by each stress treatment led to a significant decrease in total dry matter accumulation and grain yield. The most significant effects of waterlogging and combined stresses on yield occurred at the V3 stage, followed by the V6 and VT stages. However, the most significant effects of high temperature occurred at the VT stage, followed by the V6 and V3 stages. Moreover, the compound stress exacerbated damage to leaf senescence and photosynthetic properties of summer maize compared to the single stress of high temperature or waterlogging. [ABSTRACT FROM AUTHOR]

Water requirements of early‐maturing (EM) maize hybrids might be lower than those of late‐maturing (LM) maize hybrids. This study aimed to analyze the effects of different irrigation management on grain yield (GY), water uptake patterns, evaporation (E), and transpiration (T) of two maize hybrids differing in maturity via stable isotope method. The field experiment with 36 lysimeters (4‐m wide × 4‐m long) under rain‐shelters was conducted with an EM (DH518) and a mid‐maturing and LM (DH605) hybrid with three replicates from 2021 to 2022. Maize plants were grown under three irrigation amounts (W1, W2, and W3 were irrigated to maintain soil moisture at 45%, 60%, and 75% of field capacity, respectively) by flood irrigation (FI) and drip irrigation (DI) under rain‐out shelters. Results showed that GY and evapotranspiration (ET) of EM were 8% and 12% lower, while the crop water productivity (CWP) was 6% higher than that of LM. Water uptake of both hybrids occurred mainly within 0‐ to 60‐cm soil layer during the vegetative stage. Water uptake of both hybrids occurred mainly within 0‐ to 60‐cm soil layer during the vegetative stage. Summer maize under FI absorbed more water from the deep soil layer than DI in the late growth stage. Compared with LM, the water absorption depth of EM became shallower in the late growth stage. Water uptake of maize was mainly from the deeper soil under water stress conditions. E of total ET accounts for 43% under DI and 57% under FI; GY and CWP were 22% and 51% higher than those of FI. Together with choosing EM hybrids, optimization of water management with DIW3 could achieve higher GY and CWP. The optimization of irrigation method and hybrids could provide a reference for local farmers to improve GY and CWP. Core Ideas: An IsoSource model effectively determined seasonal change in water‐uptake patterns for different maize genotypes.The stable isotope technique could be an effective method to partition evaporation and transpiration.The main water absorption depth of maize changed greatly over the growth period and was affected by irrigation.The early‐maturing hybrid obtained higher crop water productivity and absorbed water from the shallower soil layer.Evaporation of total evapotranspiration accounts for 43% under drip irrigation and 57% under flood irrigation. [ABSTRACT FROM AUTHOR]

Global climate changes have led to frequent and recurrent heat stress, which has seriously affected the world maize production. The experiment presented in this paper was carried out during the maize‐growing season in 2021 and 2022 at the Huang–Huai–Hai Region Maize Science and Technology Innovation Center (36°09′N, 117°09′E) in Tai'an, Shandong province, China. The test site is located in the semi‐humid warm temperate continental monsoon climate zone, soil is brown loam. We selected different heat‐sensitive maize varieties: heat‐tolerant variety Zhengdan 958 (ZD958) and heat‐sensitive variety Xianyu335 (XY335) to study the stress effects of high temperature on the development of tassel in the key stage of its differentiation (the 12‐leaf stage, V12). We found that exposure to heat stress during the V12 stage significantly reduced the tassel size and the anther dehiscence area, making it difficult to disperse pollen, thus effectively reducing pollen production. In addition, heat stress had significant negative effects on pollen development, resulting in deformed pollen and lower pollen viability and germination rate. Our results also showed that heat stress significantly increased the activities of key reactive oxygen species‐scavenging enzymes including superoxide dismutase, peroxidase and catalase, and that the malondialdehyde and H2O2 content in tassels exposed to heat stress were significantly higher than those control group, where it should be noted that for the XY335, these effects were more pronounced than for the ZD958. The endogenous hormone content of tassels exhibited a variety of responses. After heat stress, the zeatin and salicylic acid content in tassels of both maize varieties were significantly lower than those in the respective control groups, while the abscisic acid and gibberellin acid content were significantly higher. With respect to the jasmonic acid and 3‐indoleacetic acid content, the two maize varieties exhibited opposite responses: in tassels from ZD958 plants subjected to heat stress were higher than those in the respective control group, while in tassels from XY335 plants, they were lower. The observed changes in protective enzyme activities and endogenous hormone contents induced by heat stress significantly affected the development of maize tassels and significantly reduced the amount, activity and germination rate of pollen. [ABSTRACT FROM AUTHOR]

The popularity of density‐tolerant maize (Zea mays L.) hybrids greatly increased the yield of maize hybrids in China in recent years. Clarifying trends in yield and plant density responses of agronomic characters of maize hybrids released in different years can provide theoretical and practical guidance for breeding high‐yield and density‐tolerant maize hybrids. The results showed grain yield (GY) of maize hybrids released in the 1970s and 1980s decreased with increased plant density. But GY of maize hybrids released in the 1990s and 2000s increased with a plant density increase. The GY gains from the low to high plant density plots were 86, 135, and 198 kg ha–1 per year, respectively. In all plant density treatments, yield and biomass of newer hybrids (2000s) were significantly higher than those of older hybrids (1970s). The leaf area index (LAI) of maize hybrids released in different years (1970s ∼ 2000s) increased with plant density, whereas the extinction coefficient decreased. Compared with the old hybrids, new hybrids have larger population sink capacity and stronger source supply ability, which is more prominent under high density. Population sink capacity is the main factor limiting maize yield. The key to maize hybrid improvement is to increase the population sink capacity. Breeders should continue to select for hybrids under stressful and high plant density conditions to increase seed setting rate and decrease empty ear rate of maize hybrids. Core Ideas: The planting density tolerance of the newer hybrids was higher than older ones.The newer hybrids have larger sink capacity than the older hybrids.The goal of breeding is to increase seed setting rate and decrease empty ear rate. [ABSTRACT FROM AUTHOR]

The contradiction between the high grain yield of summer maize (Zea mays L.) and greenhouse gas (GHG) emissions in the field can be resolved by selecting effective nitrogen (N) sources and fertilization methods. In this study, two fertilization methods were used: (a) urea ammonium nitrate solution (UAN) and urea (210 kg ha–1 nitrogen applied) were applied by farmers' traditional fertilization method; and (b) fertigation of four UAN application rates: CK (no N applied), AF1 (126 kg N ha–1), AF2 (168 kg N ha–1), AF3 (210 kg N ha–1). The results showed that both hybrids (DH518 and DH605) applied UAN under the traditional fertilization method increased grain yield by 2.4 and 1.8% and enhanced nitrogen use efficiency (NUE) by 25.1 and 9.9%, respectively, compared with urea. While under fertigation treatment, the grain yield increased by 7.6 and 6.6%, and the NUE increased by 23.2 and 12.4%. Grain yield increased with the increase of UAN application, and the NUE showed a trend of rising first and then falling under fertigation treatment. Both the cumulative N2O emissions and N2O emission factor showed an increasing trend as well. An application rate of UAN at 168 kg N ha–1 (AF2) resulted in a NUE that was 49% higher than urea. Compared with urea, the global warming potential (GWP) and greenhouse gas intensity (GHGI) of AF2 were reduced by 29.5% and 31.2%, respectively. These indicated that optimizing the application rate of UAN through fertigation would achieve better summer maize yield and environmental benefits. Core Ideas: This study explored how urea ammonium nitrate (UAN) application methods and rates affected yield, nitrogen use efficiency (NUE) of summer maize, and greenhouse gases (GHGs).UAN increased the grain yield and NUE of summer maize and reduced GHGs compared with urea.UAN at 168 kg N ha−1 under fertigation treatment increased grain yield and profit of summer maize. [ABSTRACT FROM AUTHOR]

Summer maize is frequently subjected to waterlogging damage because of increased and variable rainfall during the growing season. The application of 6‐benzyladenine (6‐BA) can effectively mitigate the waterlogging effects on plant growth and increase the grain yield of waterlogged summer maize. However, the mechanisms underlying this process and the involvement of 6‐BA in relevant signal transduction pathways remain unclear. In this study, we explored the effects of 6‐BA on waterlogged summer maize using a phosphoproteomic technique to better understand the mechanism by which summer maize growth improves following waterlogging. Application of 6‐BA inhibited the waterlogging‐induced increase in abscisic acid (ABA) content and increased the phosphorylation levels of proteins involved in ABA signaling; accordingly, stomatal responsiveness to exogenous ABA increased. In addition, the application of 6‐BA had a long‐term effect on signal transduction pathways and contributed to rapid responses to subsequent stresses. Plants primed with 6‐BA accumulated more ethylene and jasmonic acid in response to subsequent waterlogging; accordingly, leaf SPAD, antioxidase activity, and root traits improved by 6‐BA priming. These results suggest that the effects of 6‐BA on hormone signal transduction pathways are anamnestic, which enables plants to show faster or stronger defense responses to stress. [ABSTRACT FROM AUTHOR]