| In actual production,the wheat yield is usually increased by increasing the population density and the amount of nitrogen fertilizer applied.However,excessive planting density and nitrogen fertilizer use will lead to internode growth,height of center of gravity,thinning of stem wall,and decrease of mechanical strength,thus increasing the risk of lodging,and severely reducing wheat yield or even yield.Lignin is an important component of the cell wall and plays an important role in improving the quality of stems,but high density and nitrogen fertilizer will reduce its accumulation.Therefore,clarifying the effect of density and nitrogen fertilizer on the accumulation of lignin in wheat is of great significance for the study of regulation through cultivation measures.In this study,lodging-sensitive Shannong 16(SN16)and lodging-tolerant Shannong 23(SN23)were used as experimental materials.Three nitrogen fertilizer levels of 120 kg/ha(N1),240 kg(N2)/ha and 360 kg/ha(N3)and three planting densities0.75million/ha(D1),2.25 million/ha(D2)and 3.75 million plants/ ha(D3)were designed.Physiological,anatomical and biochemical methods were used to elucidate the regulation of density and nitrogen fertilizer on the lignin metabolism between stem stalks of wheat and its relationship with lodging resistance.In order to provide some theoretical basis for optimization of lodging resistant cultivation methods and cultivation of new lodging resistant varieties of wheat.The main findings of this experiment are as follows: 1 Effects of nitrogen fertilizer and density on stem characteristics and lodging resistanceDensity and nitrogen treatment have a certain regulatory effect on the lodging resistance of wheat stems.As the density increased,the proportion of gravity account for plant heightt,center of gravity height,and height of center of gravity of the two varieties also increased.And increased density of the first,second,the length between three also increased.The stem diameter and wall thickness also decreased with increasing density.Under the same density treatment,stem diameter and wall thickness of wheat stem increased first and then decreased from the base upward.The effect of nitrogen fertilizer on wheat stalks was basically consistent with its density.With the increase of density,the lodging resistance gradually decreased;the lodging resistance decreased from the base to the top;the lodging resistance of the lodging-resistant cultivars was significantly higher than that of lodging-sensitive cultivars,which was about twice that of lodging-sensitive cultivars.The effect of nitrogen fertilizer on wheat stalks was basically consistent with its density.The staining results showed that with the increase of density,the lignification of wheat stems was partially stained,the degree of lignification of stems was reduced,and the difference between low-density treatment and medium-high density was significant.Under D3 treatment,the arrangement of thick-walled mechanical tissue cells in the ear section becomes very loose.In terms of microstructure,the thickness of large and small vascular bundles and areas of wheat stems and thickness of thick-walled mechanical layers also tend to decrease with increasing density.The effect of nitrogen fertilizer on the anatomic structure and microstructure of stalks was similar to that of density,but the effect of nitrogen fertilizer on the thickness of wheat stem stalk was less than the effect of density on wheat stem stalk wall thickness.The correlation analysis showed that there was a very significant positive correlation between the flexion resistance and the wall thickness,the number of large vascular bundles,the total number of vascular bundles,the size of the vascular bundles,and the mechanical thickness.The thicker the stem wall,the larger the number of vascular bundles,the larger the area of vascular bundles,the thicker the mechanical tissue,the stronger the stalk resistance,which will help reduce the occurrence of lodging.2 The relationship effects of nitrogen and density on lignin metabolism and relationships with lodging resistanceDifferent densities have significant effects on the lignin content of wheat stems.In the two varieties,after planting density increased,the accumulation of lignin gradually decreased;in different internodes,the accumulation of lignin from the base gradually decreased;in different growth stages,the accumulation of lignin gradually decreased;in different varieties,the accumulation of lignin in lodging-resistant varieties was higher than lodging-sensitive varieties.The effect of nitrogen fertilizer on the accumulation of lignin in wheat differs from that of density and shows great differences in different growth periods.At the flowering stage,the accumulation of lignin in sensible SN16 increased first and then decreased with the increase of nitrogen application rate.In the filling stage,the lignin accumulation gradually decreased with the increase of nitrogen application rate.During the mature period,the accumulation of lignin increased gradually with the increase of nitrogen application rate.The pattern of even the cultivars is basically the same,but the lignin accumulation of SN23 is higher than that of SN16.Wheat stalk contains S,G and H type three lignin monomers,of which S and G type monomers are the main part,and H type monomer content is less.Among the two species,S and G monomers gradually decreased with increasing density(except for SN16 G type monomers),and H monomers did not change significantly.The proportion of S and G monomers in the second and third internodes of stems was higher than that of the other three internodes.After the density of lodging-sensitive cultivars increased,the number of S and G monomers decreased.H monomers showed an increase and then decrease at the flowering and filling stages,and they decreased at the mature stage.The S,G,and H monomers of the lodging-resistant varieties showed a gradual decrease with increasing density.In different internodes,there is a high content of S monomers in the internodes of the base.The effect of nitrogen fertilizer on the three lignin monomers in wheat stalks is different from that of nitrogen fertilizer.In the lodging-sensitive cultivars,the S and G monomers gradually decreased with the increase of N fertilizer.In the lodging-resistant cultivars,S monomers decreased with the increase of N fertilizer at the flowering and maturing stages,but the G-type monomer rises first and then declines.At the grain filling stage,the S and G monomers increase with the increase of nitrogen fertilizer.This indicated that there were differences in the regulation of nitrogen fertilizers on lignin monomers in stems.Appropriate increase of nitrogen fertilizer application could increase the ratio of S and G type monomers,which was beneficial to improve the stem lodging resistance. |
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