Effects Of Basal-topdressing Ratio Of Nitrogen Fertilizer On Grain Yield And Quality Under Heat Stress Post-anthesis In Spring Wheat

The material used in the experiment was Ning 3015,and a split-plot design was employed in the field to investigate the effects of two factors,nitrogen fertilizer application ratio and temperature,on spring wheat under high temperature stress after anthesis.The study analyzed the impact of different nitrogen fertilizer application ratios on yield and quality under high temperature stress after anthesis,and explored the mechanism by which nitrogen fertilizer application ratio alleviates the adverse effects of high temperature stress on spring wheat.The results are as follows:1.Effects of nitrogen fertilizer application ratio on photosynthetic characteristics of spring wheat under high temperature stress after anthesisAs the nitrogen fertilizer application ratio increased,the chlorophyll content,SPAD value,leaf area index,and photosynthetic fluorescence parameters of the flag leaf of spring wheat first increased and then decreased.Under high temperature stress,the SPAD value,leaf area index,chlorophyll content,and other indicators all decreased to varying degrees,with the smallest decrease in the N3 treatment.After 25 days after anthesis,under high temperature stress,the N3 treatment showed a significant increase in chlorophyll a,chlorophyll b,carotenoids,leaf area index,SPAD value,Pa,Tr,Ci,Fv/Fm,Fv/F0,and PI compared with the N1 treatment,with increases of 50.40%,72.34%,75.00%,98.53%,28.54%,80.83%,59.57%,6.12%,34.77%,72.39%,and 79.66%,respectively.Compared with the N5 treatment,the N3 treatment showed an increase of 38.54%,54.02%,85.23%,96.34%,35.83%,64.13%,42.72%,5.54%,45.29%,62.73%,and 73.16%in the same indicators.Therefore,an appropriate nitrogen fertilizer application ratio under high temperature stress can effectively slow down the degradation of chlorophyll in the flag leaf and protect PSII from damage,thereby improving photosynthesis.2.Effects of nitrogen fertilizer application ratio on nitrogen metabolism enzyme activity of spring wheat under high temperature stress after anthesisAs the nitrogen fertilizer application ratio increased,the activities of nitrate reductase,glutamine synthetase,glutamic-oxaloacetic transaminase,and alanine aminotransferase in the flag leaf of spring wheat first increased and then decreased.The N3 treatment showed the smallest decrease in activity after high temperature stress.After 25 days after anthesis,under high temperature stress,the N3 treatment showed a significant increase in nitrate reductase,glutamine synthetase,glutamic-oxaloacetic transaminase,and alanine aminotransferase activity comparedwith the N1 treatment,with increases of 90.66%,75.00%,89.44%,and 90.04%,respectively.However,the activities of endopeptidase and aminopeptidase decreased by 20.36%and 34.66%,respectively.Compared with the N5 treatment,the N3 treatment showed an increase of 82.68%,65.00%,82.39%,and 83.76%in the same indicators,while the activities of endopeptidase and aminopeptidase decreased by 29.11%and 13.51%,respectively.Therefore,an appropriate nitrogen fertilizer application ratio can effectively improve nitrogen metabolism enzyme activity,reduce protease activity,increase nitrogen uptake and transformation,and regulate nitrogen metabolism characteristics under high temperature stress.3.Effects of nitrogen fertilizer application ratio on yield and quality of spring wheat under high temperature stress after anthesisAs the nitrogen fertilizer application ratio increased,the protein content and wet gluten content of spring wheat grains and protein components showed an initial increase and then a decrease.High temperature stress significantly reduced albumin,globulin,alcohol-soluble protein,total protein,dough formation time,and dough stability time,but increased gliadin,wet gluten content,and water absorption rate.After high temperature stress,the N3 treatment showed a significant increase in albumin,globulin,alcohol-soluble protein,gliadin,totalprotein,wet gluten content,water absorption rate,dough formation time,and dough stability time compared with the N1 treatment,with increases of 57.37%,32.67%,16.24%,15.59%34.33%11.76%,10.87%,33.16%,and 32.92%,respectively.Compared with the N5 treatment,the N3 treatment showed an increase of 12.86%,10.49%,21.91%,11.09%,28.21%,11.76%,5.45%,15.53%,and 20.55%in the same indicators.Therefore,an appropriate nitrogen fertilizer application ratio can effectively alleviate the decline in grain quality caused by high temperature stress,promote the accumulation of grain protein components,and increase yield.High temperature stress reduced the number of grains per spike,thousand-grain weight,and grain weight,leading to a decrease in both yield and quality.Under the conditions of integrated water and fertilizer management for spring wheat in the Ningxia Yellow River Irrigation area with a total nitrogen application rate of 300 kg/hm2,a recommended base fertilizer to topdressing ratio of 3:7 can effectively alleviate premature senescence caused by high temperature stress after anthesis and significantly increase both yield and quality.