Effects Of Planting Density On Carbon And Nitrogen Allocation And Metabonomics Analysis Of Maize

Rational dense planting is an important measure to improve maize yield.This test in 2020 and 2021 was conducted in DOoukou test station of Northwest Agriculture and Forestry University with corn varieties Zhengdan 958 as test material to analyze effects of different planting density under different nitrogen levels on the maize biomass and the law of carbon,nitrogen accumulation and distribution,and investigate the effects of planting density on carbon and nitrogen accumulation and distribution in maize and its physiological mechanism through the analysis of gene expression,as well as the carbon and nitrogen metabolism in metabonomics analysis.The main test results are as follows:1.The results showed that dry matter accumulation per plant,100-grain weight,grain number in row and harvest index decreased with the increase of planting density.The yield of medium density treatment was the highest,and that of low density treatment was the lowest,and had a similar trend under different nitrogen levels.Under the condition of normal nitrogen application(N1),the yield of density in 2020 and 2021 was 18.20% and 17.89% higher than that of low density,respectively.In 2020 and 2021,the yield of medium density is 33.54% and 25.10% higher than that of low density,respectively.With the increase of density,starch content in leaves decreased.Grain starch content increased with the increase of density.In 2020,the grain starch content of high density and medium density under N1 condition was 0.66% and 0.82% higher than that of low density,respectively,and the grain starch content of high density was0.83% higher than that of low density under N0 condition.Increasing the density increased the nitrogen content of stem,but decreased the nitrogen content of grain,and increased the nitrogen distribution ratio between stem and cob.The contribution rate of postanthesis nitrogen accumulation to grain nitrogen decreased with increasing density.With the increase of density,the C/N ratio of leaf,stem and cob decreased,but the C/N ratio of grain increased.2.From silk-spinning stage to grain filling stage,the expression of key enzyme genes of nitrogen metabolism in leaves increased,while the relative gene expression of nitrate reductase gene(ZmNR)in leaves and roots decreased with the increase of density in both silk-spinning stage and grain filling stage.The relative gene expression level of sucrose synthase gene(ZmSH1)in leaves and roots at low density was higher than that at high density.The analysis of differential metabolites showed that in leaf carbon metabolism pathway,the content of various soluble sugars in leaves increased significantly at high density,while the content of D-mannitol in leaves decreased at high density.In the nitrogen metabolism pathway of leaves,the content of metabolites such as glutamine,aspartic acid and asparagine increased significantly under high density,which may be related to leaf senescence and nitrogen reuse.The content of soluble sugars increased in root carbon metabolism pathway,which was similar to that in leaves.In the nitrogen metabolism pathway of roots,the content of some metabolites related to stress response increased significantly at high density,but the trend was not exactly the same as that in leaves.In conclusion,the expression of key enzyme genes of carbon and nitrogen metabolism showed a decreasing trend under high density,and some metabolites related to aging showed an increasing trend.