| In this experiment,Xinhuamai 818,a newly bred variety,was used as the test material.Five nitrogen fertilizer levels were set.The relationship between root morphological changes and flag leaf photosynthesis and carbon-nitrogen metabolism under different nitrogen fertilizer levels was discussed.The contribution of root morphological changes to coordinate carbon-nitrogen metabolism,prolong leaf photosynthetic capacity and increase grain yield of winter wheat under different nitrogen fertilizer levels was studied.The correlation between photosynthetic characteristics of leaves,carbon-nitrogen metabolism,root morphological changes and grain yield was analyzed.The physiological mechanism of the effects of different nitrogen fertilizer levels on root morphology and yield of winter wheat was clarified.The optimal nitrogen fertilizer level of winter wheat under the conditions of this experiment was determined,which provided the technical basis for the efficient utilization of nitrogen fertilizer in winter wheat.The specific research results are as follows:1.Effects of different nitrogen fertilizer levels on root morphological growth parameters of winter wheatThe maximum time of root length density(TRL),root surface area(TRSA)and root volume(TRV)of winter wheat 1 meter soil is closely related to nitrogen application level.The peak values of TRL,TRSA and TRV of low nitrogen treatment appear earlier at heading stage,while the peak values of TRL,TRSA and TRV of high nitrogen treatment are postponed to flowering stage.Regardless of high nitrogen and low nitrogen treatment,the root morphological growth parameters TRL,TRSA and TRV all increase first and then decrease as the growth period advances and nitrogen application level increases.The root morphological growth parameters treated with N240 are larger than those treated with other nitrogen fertilizer levels,and the root morphological growth parameters treated with N240 are significantly slower than those treated with other treatments at the two senescence stages of flowering to grouting and grouting to maturity at the later growth stage.Compared with N0,N180,N300 and N360,the average decline of TRL,TRSA and TRV in N240 treatment from flowering to maturity increased by 50.42%,42.67%,26.72%,42.69%,78.42%,53.24%,47.80%,48.53%,75.41%,63.84%,53.75% and 73.74%,respectively.2.Effects of different nitrogen fertilizer levels on the photosynthetic performance of flag leaves of winter wheatThe net photosynthetic rate(Pn),stomatal conductance(Gs),transpiration rate(Tr)and intercellular CO2 concentration(Ci)of flag leaves of winter wheat were significantly regulated by different nitrogen fertilizer levels.The net photosynthetic rate(Pn),stomatal conductance(Gs),transpiration rate(Tr)and intercellular CO2 concentration(Ci)of wheat flag leaves could be improved by increasing the amount of nitrogen fertilizer.It was indicated that increasing nitrogen application(N240 treatment)appropriately could improve Pn,Gs,Tr and Ci of flag leaf of wheat,which was conducive to making full use of CO2,promoting synthesis and accumulation of photosynthetic products,and laid a material production foundation for high yield of wheat.Excessive application of nitrogen or no application of nitrogen would reduce these indexes,which was not conducive to accumulation of photosynthetic products,and thus affected yield.The amount of chlorophyll A,chlorophyll B and total chlorophyll in different nitrogen fertilizer levels at different growth stages after anthesis increased with the increase of nitrogen fertilizer levels,and there were also different degrees of differences among different nitrogen fertilizer levels treatments at different growth stages.The change trend of chlorophyll A/B is different from that of chlorophyll A,chlorophyll B and total chlorophyll.The value of chlorophyll A/B before flowering is 15.71% and 1.36% higher than that at filling and mature stages respectively,and chlorophyll A/B decreases with the increase of nitrogen application rate in each stage.Correlation analysis showed that chlorophyll a,chlorophyll b,total chlorophyll,chlorophyll A/B also showed a Quadratic function relationship with yield.Therefore,while increasing chlorophyll content,the ratio of chlorophyll A/B should be coordinated,and the nitrogen application rate should be controlled at 240-300 kg hm-2,which is conducive to the synthesis and accumulation of photosynthetic products in wheat and the improvement of grain yield.3.Effects of different nitrogen fertilizer levels on nitrogen-carbon metabolic enzyme activities in flag leaves of wheatThe activities of nitrate reductase(NR)and Glutamine synthetase(GS)in flag leaves of wheat showed a trend of increasing first and then decreasing with the development of growth period,and NR activity reached its peak in flowering period,while GS activity reached its maximum in filling period.The activity of NR in flowering stage was N360,N300>N240,N180 > N0,which was 25.66%,19.23%,17.34%,9.65% higher than N0 respectively.The GS activity of each treatment in grouting stage was N360,N300>N240,N180 and N0,which were 46.28%,29.56%,18.84% and 7.32% higher than N0 respectively.The activities of flag leaf phosphosucrose synthetase(SPS)and phosphate synthetase(SS)both changed in a "convex" shape with the development of growth period.The activities of SPS and SS in flowering period were the highest in N240 treatment,which increased 59.05%,28.83%,24.54%,33.85% and 32.69%,6.47%,1.83% and 5.54% respectively compared with N0,N180,N300 and N360 treatments.Correlation analysis showed that the activity and yield of SPS and SS were also correlated by a quadratic function,and there was a significant positive correlation between the activity and yield of SPS and SS in flowering period,but no significant correlation in other growth periods.While GS activity and NR activity were correlated with yield in a quadratic function and the equation curve was consistent,but the correlation significance was different.The correlation coefficient between GS activity and yield reached a significant level,while NR was not.It can be seen that proper n application is conducive to improving the enzyme activities of SS,SPS,NR and GS in flag leaves of wheat,enhancing the carbon and nitrogen metabolism of plants,and facilitating the transport of assimilation products produced by photosynthesis to grains.This is the physiological basis for rational nitrogen fertilizer to achieve high wheat yield.4.Effects of different nitrogen fertilizer levels on wheat yield and its componentsNitrogen application was controlled at 0-300 kg hm-2,unit effective panicle number and grain number per panicle were gradually increased,but 1000-grain weight was gradually decreased,grain yield first increased and then decreased,and nitrogen application reached 360 kg hm-2,yield and its three components were reduced to different degrees.The effect of nitrogen level treatment on the agronomic efficiency of wheat showed that the agronomic efficiency of nitrogen fertilizer decreased with the increase of nitrogen level.Based on the simulation equation of nitrogen application and grain yield,and taking yield and nitrogen utilization efficiency into account,the optimal nitrogen application was 263.07 kg hm-2 under the conditions of this experiment,and the maximum theoretical yield was 8548.80 kg hm-2. |
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