Changes In Meteorological Factors Affecting Nitrogen Metabolism Characteristics Of Spring Maize Varieties With Different Nitrogen Efficiency

Inner Mongolia region is located in the northern border of China,mainly engaged in agricultural and animal husbandry production,and spring maize is the main crop planted in this area.Nitrogen is a nutrient element that is in high demand during the growth and development of maize,and is also one of the factors that determine maize yield and quality.During the maize planting process,there is a phenomenon of unreasonable and unbalanced nitrogen fertilizer application,resulting in low fertilizer utilization efficiency.However,with the continuous improvement of maize yield,its protein content has a decreasing trend year by year,seriously affecting the nutritional quality of maize.In maize production,in order to promote the synchronous improvement of yield and quality,reasonable fertilization is an important issue that needs to be urgently solved.This study analyzed the spatiotemporal evolution characteristics of agricultural climate resources such as sunlight,temperature,and precipitation in Inner Mongolia from 1960 to 2020,and their impact on spring maize yield.The temperature,light,water and comprehensive suitability models of spring maize at different growth stages were constructed,and the Growing region of spring maize in Inner Mongolia were divided according to the suitability.Three Ecotope,namely Wuyuan County of Bayannur City,a low value area of climate suitability,Tumed Right Banner of Baotou City,a medium value area,and Harqin Banner of Songshan District of Chifeng City,a high value area,were selected to conduct a combination of field and artificial climate box experiments using different nitrogen efficiency maize varieties Xianyu 335（XY335）,Zhengdan 958（ZD958）,and Jingke 968（JK968）as experimental materials,Set three nitrogen fertilizer levels(field:0 kg·hm^-2,150 kg·hm^-2,300 kg·hm^-2;artificial climate box:0g·Basin^-1,0.97g·Basin^-1,1.94g·Basin^-1).Study the effects of nitrogen fertilizer levels in different ecological regions on the accumulation,transportation,and utilization of dry matter and nitrogen in spring maize varieties XY335,ZD958,and JK968.Clarify the differences in amino acid and protein content and their components in the grains of different spring maize varieties,as well as the dynamic changes in the activities of key enzymes involved in nitrogen metabolism,in order to reveal the regulatory effect of nitrogen application on protein from a physiological and biochemical perspective.The main research findings are as follows:1.By summarizing the main climatic resources during the growth period of spring maize,the cultivation patterns and climate suitability changes of spring maize in Inner Mongolia were analyzed.The results showed that the planting boundaries of different maturity types of spring maize showed a clear trend of extending northward and eastward,with the largest change occurring in the central and eastern regions,transitioning from unsuitable planting areas to early and medium early maturing areas;The Northeast region shows a decrease in unsuitable planting areas and an increase in early maturing areas.The overall climate suitability of spring maize planting areas in Inner Mongolia is showing an upward trend,with high value areas mainly located in the central and southeastern regions,with a clear northward extension of the boundary.2.The dry matter accumulation of maize varieties XY335,ZD958 and JK968 in different Ecotope was shown as the high value area in Harqin Banner,while the low value area in Wuyuan County and the middle value area in Tumed Right Banner.The nitrogen efficient varieties XY335 and ZD958 have good post flowering dry matter production capacity.With the advancement of maize growth and development,the proportion of dry matter and nitrogen distribution in XY335,ZD958,and JK968 leaves gradually decreased from V6 to R6 stages.The distribution ratio of stem dry matter and nitrogen showed a trend of first increasing and then decreasing from V6 to R6.The distribution ratio of dry matter and nitrogen in stems increased first and then decreased from V6 to R6.The distribution ratio of dry matter and nitrogen in maize cob+bract leaves increased first and then decreased from VT stage to R6 stage.The distribution ratio of dry matter in grains showed an upward trend from R3 to R6.At low nitrogen levels,it is not conducive to the growth and dry matter accumulation of maize,while at medium and high nitrogen levels,it can promote rapid growth and dry matter accumulation of maize.In terms of dry matter transport,RAP,PRAR,CPAR,and APA showed an upward trend with the increase of nitrogen application level.In terms of nitrogen transport,both NRA and CNRA show a gradually increasing trend,while NRR shows a trend of first increasing and then decreasing.NAG shows a gradually increasing trend,while CNAG shows a gradually decreasing trend.In terms of nitrogen utilization,NPE,NRE,NAE,NPFP,and NHI showed a decreasing trend with the increase of nitrogen application level.The activities of key enzymes in nitrogen metabolism showed significant differences in different ecological regions,including NR activity,Ni R activity,GS activity,GOGAT activity,and AS activity in the leaves of maize varieties XY335,ZD958,and JK968,all showing an upward trend with the increase of nitrogen application levels.For grains,the Ni R activity of XY335,JK968,and ZD958 increased with the increase of nitrogen application level,while the NR,GS,and GOGAT activities of XY335 and ZD958 increased with the increase of nitrogen application level.The NR,GS,and GOGAT activities of JK968 were better at low nitrogen levels,while the AS activity of XY335,JK968,and ZD958 grains was better at low nitrogen levels.3.The ecological zone has a significant impact on the number of panicles and thousand grain weight,while nitrogen fertilizer has a significant impact on the number of grains per panicle and yield.In different ecological regions,maize varieties XY335,ZD958,JK968 showed a significant upward trend in terms of panicle number,grain number per panicle,thousand grain weight,and yield with the increase of nitrogen application level（N2>N1>N0）.The N2 level increased by 12.77%,20.27%,11.53%,and50.98%compared to the N0 level,and the N2 level increased by 5.65%,6.12%,3.73%,and 16.22%compared to the N1 level,respectively.Under the N0 level,the yield of Tumed Right Banner was XY335>JK968>ZD958,and the yield difference among varieties was significant（P<0.05）;At the N1 and N2 levels,the yield performance was ZD958>JK968>XY335,and the yield difference between varieties was significant（P<0.05）.Under different nitrogen application levels in Wuyuan County and Karaqin Banner,the yield was shown to be ZD958>JK968>XY335.4.Ecological zone,nitrogen fertilizer,variety and ecological zone×Nitrogen fertilizer,ecological zone×Variety and nitrogen fertilizer×Varieties and ecological zones×nitrogenous fertilizer×The interaction effect of the three factors of the variety has a significant impact on the protein content of corn grains.The protein content in the grains of the three tested varieties showed the following pattern:Tumed Right Banner experimental site>Wuyuan County experimental site>Karaqin Banner experimental site.The protein content in grains shows an upward trend with the increase of nitrogen application level.The grain protein content showed an upward trend with the increase of nitrogen application level,N2>N1>N0.The amino acid content of grains is characterized by high content of glutamic acid,proline,and leucine,accounting for about 46%to 61%of the total amino acid content,while low content of aspartic acid,serine,arginine,methionine,and tryptophan,accounting for about 8%to 12%of the total amino acid content.By using the amino acid ratio coefficient method,the RAA and RCAA values of leucine,tryptophan,tyrosine+phenylalanine,and cysteine+methionine are all greater than 1,and lysine is the first limiting amino acid.The SRCAA values of XY335 in Wuyuan County,JK968 in Karaqin Banner and Wuyuan County,and ZD958 in Karaqin Banner are higher,and the overall SRCAA value shows an upward trend with the improvement of nitrogen application level.5.By establishing a stepwise regression equation and principal component analysis of climate factors,climate suitability,and yield,the results showed that temperature is the key factor affecting meteorological yield,followed by sunshine hours and climate suitability,and precipitation and humidity are the third limiting factors.The simulation of enzyme activity changes in maize leaves in different ecological regions using an artificial climate box is consistent with the pattern of enzyme activity changes in field leaves,indicating that increasing nitrogen fertilizer application can improve the key enzyme activity of nitrogen metabolism in maize leaves.In summary,the overall climate suitability of spring maize planting areas in Inner Mongolia is showing an upward trend.The dry matter accumulation,nitrogen distribution ratio,and key enzyme activities of nitrogen metabolism of maize varieties in different ecological regions are all showing an upward trend with the increase of nitrogen application levels.Ecological zones,nitrogen fertilizers,varieties,and their interactions have significant effects on maize yield,protein and amino acid content.Through stepwise regression and principal component analysis,it was found that temperature,sunshine hours,and climate suitability are key factors affecting meteorological yield.The simulation results of the artificial climate box are consistent with the results of field experiments,indicating that nitrogen application can improve the activity of key enzymes in nitrogen metabolism in maize leaves.