本研究探讨从华北平原引入优质品种，减少氮肥施用量，提高青藏高原小麦质量和产量的可行性。试验选用青藏高原3个小麦品种和北部冬麦区4个小麦品种，于拔节期减少氮肥追施量，分别在海拔3647 m的青藏高原拉萨和海拔4 m的北部冬麦区河北任丘种植。小麦种在拉萨条件下，北部冬麦区小麦品种相比青藏高原小麦品种表现出较高的籽粒硬度和容重，以及较好的面粉和面团质量。在拔节期将氮肥追施量从135 kg N ha^-1减少到75 kg N ha^-1（氮肥基施量相同，均为105 kg N ha^-1）对两地种植的小麦籽粒产量、籽粒质量、面粉质量、面团质量均没有显着影响（P<0.05）。总体来看，从华北平原引进优质小麦品种到青藏高原种植，并且减少拔节期的氮肥施用量，这是一种提高青藏高原小麦质量的经济实用方法。

Wheat was the first crop grown in Egypt, and it remains highly important.  Egypt is the largest wheat importer in the world and consumes an extensive amount of bread.  It is imperative for wheat scientists to decrease the large gap between production and consumption.  Wheat yields in Egypt increased 5.8-fold (6.7 billion kg) between 1961 and 2017 due to variety improvement and the use of better planting methods such as the raised bed method, ideal sowing date, surge flow irrigation and farm irrigation systems, laser levelling, fertilizers, and intercropping with raised beds.  In this paper, the development of wheat production techniques and variety evolution over more than five decades in Egypt have been analyzed.  In particular, we have focused on the technologies, cultural practices and causes for per unit area yield increase.  The main purpose was to study the issues that have arisen during wheat production and to make recommendations for smart agricultural practices.  In 1981, the yield was 3 300 kg ha^–1 and through the improvement of varieties, expansion of agricultural land and the adoption of modern agricultural techniques yield reached 6 500 kg ha^–1 by 2017.  The production growth rate was 4.1% annually, and the total grain yield increased 4.3-fold, from 1.9 billion kg in 1981 to about 8.1 billion kg in 2017.  The use of new improved varieties, new cultivation techniques, and modern irrigation techniques contributed to 97.0% of the increase in yield per unit area and 1.5% of the increase in yield was due to planting area expansion.  Therefore, the increase in total yield mainly depended on the increase in yield per unit area.  Wheat production in Egypt has been improved through the development of breeding and cultivation techniques.  The use of these new techniques, the popularization of new high-quality seed varieties, and the use of the raised bed method instead of the old method of planting in basins have made the largest contributions to increased yield.  In the future, wheat yield could be further increased by using the tridimensional uniform sowing mode and the development of wheat varieties that are resistant to rusts, deficit irrigation, and abiotic stress, that are highly adaptable to mechanized operation and have high yields.  Based on our analysis, we propose the main technical  requirements and measures to increase wheat yield in Egypt in the near future.

Improving radiation use efficiency (RUE) of the canopy is necessary to increase wheat (Triticum aestivum) production.  Tridimensional uniform sowing (U) technology has previously been used to construct a uniformly distributed population structure that increases RUE.  In this study, we used tridimensional uniform sowing to create a wheat canopy within which light was spread evenly to increase RUE.  This study was done during 2014–2016 in the Shunyi District, Beijing, China.  The soil type was sandy loam.  Wheat was grown in two sowing patterns: (1) tridimensional uniform sowing (U); (2) conventional drilling (D).  Four planting densities were used: 1.8, 2.7, 3.6, and 4.5 million plants ha^–1.  Several indices were measured to compare the wheat canopies: photosynthetic active radiation intercepted by the canopy (IPAR), leaf area index (LAI), leaf mass per unit area (LMA), canopy extinction coefficient (K), and RUE.  In two sowing patterns, the K values decreased with increasing planting density, but the K values of U were lower than that of D.  LMA and IPAR were higher for U than for D, whereas LAI was nearly the same for both sowing patterns.  IPAR and LAI increased with increasing density under the same sowing pattern.  However, the difference in IPAR and LAI between the 3.6 and 4.5 million plants ha^–1 treatments was not significant for both sowing patterns.  Therefore, LAI within the same planting density was not affected by sowing pattern.  RUE was the largest for the U mode with a planting density of 3.6 million plants ha^–1 treatment.  For the D sowing pattern, the lowest planting density (1.8 million plants ha^–1) resulted in the highest yield.  Light radiation interception was minimal for the D mode with a planting density of 1.8 million plants ha^–1 treatment, but the highest RUE and highest yield were observed under this condition.  For the U sowing pattern, IPAR increased with increasing planting density, but yield and RUE were the highest with a planting density of 3.6 million plants ha^–1.  These results indicated that the optimal planting density for improving the canopy light environment differed between the sowing patterns.  The effect of sowing pattern×planting density interaction on grain yield, yield components, RUE, IPAR, and LMA was significant (P<0.05).  Correlation analysis indicated that there is a positive significant correlation between grain yield and RUE (r=0.880, P<0.01), LMA (r=0.613, P<0.05), and spike number (r=0.624, P<0.05).  These results demonstrated that the tridimensional uniform sowing technique, particularly at a planting density of 3.6 million plants ha^–1, can effectively increase light interception and utilization and unit leaf area.  This leads to the production of more photosynthetic products that in turn lead to significantly increased spike number (P<0.05), kernel number, grain weight, and an overall increase in yield.

High-temperature stress (HTS) at the grain-filling stage in spring maize (Zea mays L.) is the main obstacle to increasing productivity in the North China Plain (NCP). To solve this problem, the physiological mechanisms of HTS, and its causes and impacts, must be understood. The HTS threshold of the duration and rate in grain filling, photosynthetic characteristics (e.g., the thermal stability of thylakoid membrane, chlorophyll and electron transfer, photosynthetic carbon assimilation), water status (e.g., leaf water potential, turgor and leaf relative water content) and signal transduction in maize are reviewed. The HTS threshold for spring maize is highly desirable to be appraised to prevent damages by unfavorable temperatures during grain filling in this region. HTS has negative impacts on maize photosynthesis by damaging the stability of the thylakoid membrane structure and degrading chlorophyll, which reduces light energy absorption, transfer and photosynthetic carbon assimilation. In addition, photosynthesis can be deleteriously affected due to inhibited root growth under HTS in which plants decrease their water-absorbing capacity, leaf water potential, turgor, leaf relative water content, and stomatal conductance. Inhibited photosynthesis decrease the supply of photosynthates to the grain, leading to falling of kernel weight and even grain yield. However, maize does not respond passively to HTS. The plant transduces the abscisic acid (ABA) signal to express heat shock proteins (HSPs), which are molecular chaperones that participate in protein refolding and degradation caused by HTS. HSPs stabilize target protein configurations and indirectly improve thylakoid membrane structure stability, light energy absorption and passing, electron transport, and fixed carbon assimilation, leading to improved photosynthesis. ABA also induces stomatal closure to maintain a good water status for photosynthesis. Based on understanding of such mechanisms, strategies for alleviating HTS at the grain-filling stage in spring maize are summarized. Eight strategies have the potential to improve the ability of spring maize to avoid or tolerate HTS in this study, e.g., adjusting sowing date to avoid HTS, breeding heat-tolerance varieties, and tillage methods, optimizing irrigation, heat acclimation, regulating chemicals, nutritional management, and planting geometric design to tolerate HTS. Based on the single technology breakthrough, a comprehensive integrated technical system is needed to improve heat tolerance and increase the spring maize yield in the NCP.  

The grain yield of maize has increased continuously in past decades, largely through hybrid innovation, cultivation technology, and in particular, recent genetic improvements in photosynthesis. Elite inbred lines are crucial for innovating new germplasm. Here, we analyzed variations in grain yield and a series of eco-physiological photosynthetic traits after anthesis in sixteen parental lines of maize (Zea mays L.) released during three different eras (1960s, 1980s, 2000s). We found that grain yield and biomass significantly increased in the 2000s than those in the 1980s and 1960s. Leaf area, chlorophyll, and soluble protein content slowly decreased, and maintained a higher net photosynthesis rate (Pn) and improved stomatal conductance (Gs) after anthesis in the 2000s. In addition, the parental lines in the 2000s obtained higher actual photochemistry efficiency (ФPSII) and the maximum PSII photochemistry efficiency (Fv/Fm), which largely improved light partitioning and chlorophyll fluorescence characteristic, including higher photochemical and photosystem II (PSII) reaction center activity, lower thermal energy dissipation in antenna proteins. Meanwhile, more lamellae per granum within chloroplasts were observed in the parental lines of the 2000s, with a clear and complete chloroplast membrane, which will greatly help to improve photosynthetic capacity and energy efficiency of ear leaf in maize parental lines. It is concluded that grain yield increase in modern maize parental lines is mainly attributed to the improved chloroplast structure and more light energy catched for the photochemical reaction, thus having a better stay-green characteristic and stronger photosynthetic capacity after anthesis. Our direct physiological evaluation of these inbred lines provides important information for the further development of promising maize cultivars.

High temperature stress (HTS) on spring maize (Zea mays L.) during the filling stage is the key factor that limits the yield increase in the North China Plain (NCP). Subsoiling (SS) and ridge tillage (R) were introduced to enhance the ability of spring maize to resist HTS during the filling stage. The field experiments were conducted during the 2011 and 2012 maize growing seasons at Wuqiao County, Hebei Province, China. Compared with rotary tillage (RT), the net photosynthetic rate, stomatal conductance, transpiration rate, and chlorophyll relative content (SPAD) of maize leaves was increased by 40.0, 42.6, 12.8, and 29.7% under SS, and increased by 20.4, 20.0, 5.4, and 14.2% under R, repectively. However, the treatments reduce the intercellular CO2 concentration under HTS. The SS and R treatments increased the relative water content (RWC) by 11.9 and 6.2%, and the water use efficiency (WUE) by 24.3 and 14.3%, respectively, compared with RT. The SS treatment increased the root length density and soil moisture in the 0-80 cm soil profile, whereas the R treatment increased the root length density and soil moisture in the 0-40 cm soil profile compared with the RT treatment. Compared with 2011, the number of days with temperatures 33°C was more 2 d and the mean day temperature was higher 0.9°C than that in 2012, whereas the plant yield decreased by 2.5, 8.5 and 10.9%, the net photosynthetic rate reduced by 7.5, 10.5 and 18.0%, the RWC reduced by 3.9, 5.6 and 6.2%, and the WUE at leaf level reduced by 1.8, 5.2 and 13.1% in the SS, R and RT treatments, respectively. Both the root length density and the soil moisture also decreased at different levels. The yield, photosynthetic rate, plant water status, root length density, and soil moisture under the SS and R treatments declined less than that under the RT treatment. The results indicated that SS and R can enhance the HTS resistance of spring maize during the filling stage, and led to higher yield by directly improving soil moisture and root growth and indirectly improving plant water status, photosynthesis and grain filling. The study can provide a theoretical basis for improving yield of maize by adjusting soil tillage in the NCP.