Abscisic acid (ABA) plays a physiological role in regulating the heat tolerance of plants and maintaining crop productivity under high-temperature stress. Appropriate cultivation techniques can regulate endogenous ABA and help farmers improve food production under high-temperature stress. Here, the physiological basis for ABA-induced heat tolerance in crops is reviewed. High-temperature stress stimulates ABA, which reduces stomatal opening and promotes root growth. The root system absorbs water to maintain the water status, thus allowing the plant to maintain physiological activities under high-temperature stress. ABA plays a synergistic role with nicotinamide adenine dinucleotide biosynthesis to improve the thermal stability of the cell membrane, maintain a dynamic balance between material and energy, and reduce the negative effects of high-temperature stress on kernel number and kernel weight. Cultivation and tillage techniques adapted to high-temperature stress, such as adjustment of sowing time, application of plant growth regulators and fertilizers, and the use of irrigation, subsoiling and heat acclimation, and the mechanisms by which they improve crop heat tolerance, are also reviewed. The results of the studies reviewed here will help researchers develop techniques for cultivating food crops under heat stress and apply them to food-production fields to improve crop productivity.

The maize sole cropping system solves problems related to ground water resource shortages and guarantees food security in the North China Plain. Using optimal sowing dates is an effective management practice for increasing maize yield. The goal of this study was to explore an optimum sowing date for high-yield maize. Six sowing dates (SDs) from early April to late June with intervals of 10 to 20 days between SD—SD1 (early April), SD2 (mid to late April), SD3 (early May), SD4 (mid to late May), SD5 (early June), SD6 (late June)—were applied from 2012 to 2017. The results showed that yield was correlated with the sowing date based on the thermal time before sowing (r = 0.62**), which was defined as the pre-thermal time (PTt), and that the yield was steadily maintained at a high level (>10,500 kg ha⁻¹) when PTt was greater than 479 °C. To satisfy the growing degree-days required for maturity, maize needs to be sown before a PTt of 750 °C. Data analysis of the results from 2014, 2015, and 2017 revealed the following: i) Most of the grain-filling parameters of late-sown dates (SD4, SD5 and SD6) were better than those in early-sown dates (SD1, SD2, and SD3) in all years, because of the high daily maximum temperature (Tmax) and wide diurnal temperature (Td) from silking to blister (R1–R2) of early-sown dates. The weight of maximum grain-filling rate (Wmax) of SD3 decreased compare with SD4 by the narrow Td from blister to physiological maturity (R2–R6) in all years (−5, −12, and −33 mg kernel⁻¹ in 2014, 2015, and 2017, respectively). ii) In 2017, the pollination failure rates of early-sown dates were 8.4~14.5%, which was caused by the high Tmax and Td of R1–R2. The apical kernel abortion rates were 28.6 (SD2) and 38.7% (SD3), which were affected by Tmax and Td during R2–R6. iii) Compared with late-sown dates, the wide Td of early-sown dates in R1–R2 was caused by higher Tmax, but the narrow Td in R2-R6 was caused by higher Tmin. Our results indicate that high-yielding maize can be obtained by postponing the sowing date with a PTt of 480~750 °C, which can prevent the negative effects of the high Tmax of R1–R2 and high Tmin of R2–R6 on kernel number and weight formation. Moreover, these above-mentioned traits should be considered for heat tolerance breeding to further increase the maize yield.

Innovative approaches to enhance N fertilization to improve season-long N availability are essential to optimal sorghum (Sorghum bicolor, (L.) Moench.) productivity and N use efficiency. A two-year field experiment was conducted in the 2020 and 2021 summer seasons on the North China Plain to determine the effects of a novel urea coated with polyaspartic acid (PAA) (PN) and a control treatment (CN) on grain sorghum yield and N utilization characteristics at four N application rates (0, 60, 120, and 240 kg ha⁻¹). The results showed that sorghum yield, agronomic traits (including leaf area duration (LAD), crop growth rate (CGR), and dry matter accumulation (DMA)), the accumulation of nitrate N and ammonium N in the 0–60 cm soil layer, stover and grain N content, and total N uptake (NUT) in 2020 and 2021 significantly increased as N application rates increased from 0 to 240 kg ha⁻¹, whereas nitrogen agronomic efficiency (NAE), N uptake efficiency (NUpE), and N utilization efficiency (NUtE) varied inversely with increasing N application rates. Compared to CN, PN demonstrated a significant enhancement in grain sorghum yield, LAD, and CGR, from 3.3% to 7.1%, from 4.8% to 6.1%, and from 5.8% to 6.8%, respectively, at 60 and 120 kg N ha⁻¹. PN improved the N availability (mainly nitrate-N) in the sorghum soft dough and the stover and grain N content at harvest and NUT, NUpE, and NAE accordingly compared with CN at the 60 and 120 kg ha⁻¹ N application rates. In short, our two-year field trials demonstrated that PN with 120 kg N ha⁻¹ is recommended in grain sorghum to optimize sorghum productivity and nitrogen use efficiency at the current yield level in the North China Plain.

GDP-L-galactose phosphorylase (GGP) is a key rate-limiting enzyme in the ascorbic acid synthesis pathway, and it plays a crucial role in regulating ascorbic acid metabolism and redox balance. The upstream open reading frame (uORF) in the 5' untranslated region of the GGP gene typically suppresses translation efficiency, reducing vitamin C content. In this study, GGP uORF in rice was identified, and seven GGP uORF allele variants AL1-AL7 were generated by CRISPR/Cas9 technology; then, the effects of these variations on AsA content and osmotic stress resistance were evaluated. The AsA content of the seven mutant plants was 1.80-3.08 times greater than that of the control, and the increase of AL4 mutant was the greatest. Protoplast assays confirmed that the OsGGP uORF inhibits downstream ORF translation. Osmotic stress experiments revealed that in the mutant lines, both the activities of enzymes involved in reactive oxygen species (ROS) scavenging and the proline (Pro) content were significantly increased, while the levels of peroxides were significantly decreased. These results demonstrate that mutation of the GGP uORF significantly increases translation efficiency, AsA content, and the ability of rice to reduce ROS levels, restore osmotic balance, and improve ROS scavenging capacity under osmotic stress. This study reports the regulated osmotic stress of the GGP uORF in monocotyledonous plants for the first time and has created a variety of allelic variation germplasm resources. It provides a novel approach for improving AsA content and tolerance to salt stress in rice and other monocots via genetic approaches.

Innovative measures of nitrogen (N) fertilization to increase season-long N availability is essential for gaining the optimal foxtail millet (Setaria italica L. Beauv.) productivity and N use efficiency. A split plot field experiment was conducted using the foxtail millet variety Huayougu 9 in 2020 and 2021 in Northeast China to clarify the physiological mechanism of a novel polyaspartic acid–chitosan (PAC)-coated urea on N assimilation and utilization from foxtail millet. Conventional N fertilizer (CN) and the urea-coated -PAC treatments were tested under six nitrogen fertilizer application levels of 0, 75, 112.5, 150, 225, and 337.5 kg N ha⁻¹. The results showed that compared to CN, PN increased the foxtail millet yield by 5.53–15.75% and 10.43–16.17% in 2020 and 2021, respectively. PN increased the leaf area index and dry matter accumulation by 7.81–18.15% and 12.91–41.92%, respectively. PN also enhanced the activities of nitrate reductase, glutamine synthetase, glutamic oxaloacetic transaminase, and glutamic–pyruvic transaminase, thereby increasing the soluble protein in the leaf, plant, and grain N content at harvest compared to CN. Consequently, partial factor productivity from applied N, the agronomic efficiency of applied N, recovery efficiency of applied N, and physiological efficiency of applied N of foxtail millet under PN treatments compared to CN were increased. The improvement effect of the items above was more noticeable under the low–middle N application levels (75, 112.5, and 150 kg N ha⁻¹). In conclusion, the PAC could achieve the goal of high yield and high N use efficiency in foxtail millet under the background of a one-time basic fertilizer application.