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Post-silking heat stress is one of the main stresses affecting grain filling and yield formation of summer maize in the Huang-Huai-Hai plains. At present, it has been confirmed that increasing nitrogen application can alleviate the inhibition of post-silking heat stress on the yield formation of wheat, maize, and rice, but the regulatory pathways and physiological mechanisms remain unclear. In this study, two maize varieties Zhengdan 958 (ZD958) and Xianyu 335 (XY335) were selected in pot experiment. To study the effects of increased nitrogen application on carbon and nitrogen metabolism of maize under heat stress during post-silking stage, two temperature treatments [ambient temperature (CK) and heat stress (HS)], three nitrogen application levels [low nitrogen application rate (LN): 120 kg hm-2, middle nitrogen application rate (MN): 240 kg hm-2, and high nitrogen application rate (HN): 360 kg hm-2] were set. The results showed that the dry weight of ZD958 and XY335 cultivars at maturity stage decreased by 10.6%-19.3% after 20 days of post-silking heat stress (35°C) compared with the ambient temperature. However, the decrease of kernel dry weight under heat stress was gradually decreased with the increase of nitrogen application rate, and the decrease rate (10.6%-11.2%) of kernel dry weight under medium nitrogen application rate (MN) and high nitrogen application rate (HN) was lower than that (16.2%-19.3%) under low nitrogen application rate (LN), which indicating that increased nitrogen application could significantly increase maize kernel dry weight under post-silking heat stress. This was mainly due to the increasing application of nitrogen effectively alleviated the inhibitory effect of early post-silking heat stress on maize grain nitrogen metabolism, and significantly increased the activities of key enzymes of nitrogen metabolism such as glutamine synthetase (GS) and glutamate synthetase (GOGAT). At the same time, the activities of sucrose phosphate synthetase (SPS) and sucrose synthetase (SS), which were key enzymes of carbon metabolism, were maintained, and the synthesis of soluble sugar in grains was increased, thus ensuring a larger amount of material for grain filling. In conclusion, increasing nitrogen application can alleviate the inhibition of post-silking heat stress on grain carbon and nitrogen metabolism and promote the accumulation of assimilates in grain and increase the kernel weight and yield, which provides a way for the resistant cultivation of summer maize in the Huang-Huai-Hai plains. [ABSTRACT FROM AUTHOR]

Clarifying the characteristics of annual yield, distribution and utilization of climatic resources, and establishing rational quantitative indexes of annual climatic resources distribution for different cropping systems are helpful to provide theoretical basis for further improving annual yield and resource use efficiency in the Yellow-Huaihe-Haihe Rivers plain. In this study, the experiment was conducted from 2011 to 2015 at Xinxiang, Henan province to analyze the grain yield, biomass, dry matter production energy, and distribution and utilization efficiency of climatic resources under four cropping systems, namely winter wheat-summer maize, winter wheat-summer soybean, double maize and one-season spring maize. There were no differences in the annual grain yield, total biomass, and dry matter production energy between the winter wheat-summer maize and double maize cropping systems, but they were significantly higher than those of the winter wheat-summer soybean and one-season spring maize cropping systems, with an average increase of 45.4%-61.5%, 37.3%-71.3%, and 35.77%-70.7%, respectively. The annual radiation production efficiency, radiation use efficiency of grain and total biomass for double maize and one-season spring maize cropping systems were significantly higher than those of the winter wheat-summer maize and winter wheat-summer soybean cropping systems, with an average increase of 11.8%-66.7% in the annual radiation production efficiency, and 0.13-0.42 and 0.18-0.69 percentage points increase in the radiation use efficiency of grain and total biomass, respectively. The accumulative temperature distribution rate for two seasons of winter wheat-summer maize was 45.6% and 54.4%, respectively, while those of double maize was 51.4% and 48.6%, respectively. The accumulative temperature ratio between two seasons was of winter wheat-summer maize 0.8, while that of double maize was 1.1. Considering both yield and resource use efficiency, winter wheat-summer maize and double maize cropping systems can be used to optimize the layout of planting patterns and support the sustainable development of agricultural production in the Yellow-Huaihe-Haihe Rivers plain. Furthermore, clarifying the accumulated temperature distribution rate and the accumulated temperature ratio between two seasons is helpful to optimize climate resource distribution, and further improve the yield potential and the resources use efficiency of double cropping system in the Yellow- Huaihe-Haihe Rivers plain. [ABSTRACT FROM AUTHOR]