| Wheat is one of the important food crops in the world.Improving wheat production and nitrogen absorption and utilization efficiency is an important strategy to solve global food security and protect the ecological environment.Shaanxi Province is one of the traditional superior bases for the improvement of winter wheat varieties and the propagation and supply of fine winter wheat seeds.This area is a typical dry farming and rain-fed agricultural area,and water deficit is also the main factor limiting wheat production.Therefore,to clarify the change trend of nitrogen fertilizer on winter wheat yield and water and nitrogen use traits in dry land during the variety replacement process provides theoretical guidance for wheat yield improvement and selection of traits in breeding.In this study,a wide variety of wheat varieties from the wheat region of Shaanxi Province from 1940s to 2010s were selected.The field test system was used to analyze the yield and composition factors,main agronomic traits,dry matter accumulation,The evolution of photosynthetic characteristics and nitrogen uptake and utilization characteristics in leaves and ears;and the relationship between plant physiology and water and nitrogen use efficiency under different water and nitrogen interactions was studied using pot water control experiments,and the following conclusions were obtained,?1?The grain yield of winter wheat in Shaanxi from 1940s to 2010s increased significantly with the increase of nitrogen fertilizer application levels.Under the same nitrogen application level,the grain yield of wheat gradually increased with the improvement of the variety,and the response of modern varieties to nitrogen fertilizer increased.The grain yield varied from 4258 kg·ha-1?1940s?to 6578 kg·ha-1?2010s?under N180 treatment.The results of the two-year average data show that,in the process of variety replacement,the yield has a very significant positive correlation with the 1000-grain weight and the harvest index.During the variety improvement process,modern wheat varieties approached the ideal plant height,and the plant heights of wheat varieties gradually stabilized after 2000s.The change of tiller number in each period of wheat showed a trend of first increase and then decrease with the variety improvement process,Modern varieties show strong dry matter accumulation ability and adaptability to nitrogen;promoting vegetative growth before jointing of wheat is also one of the biological foundations for yield improvement.?2?The nitrogen use efficiency of wheat has increased significantly with the improvement of varieties,Modern cultivars 2000s and 2010s showed superior characteristics in nitrogen utilization and nitrogen partial productivity.In addition,cultivar improvement coordinated the distribution of nitrogen at all stages of growth,making nitrogen transport before and after flowering and its contribution to the grain more balanced.Compared with N0 treatment,N120 and N180 treatments increased the nitrogen accumulation of wheat by15.38%and 21.75%,respectively.The increase of nitrogen distribution in leaves may be the main reason for the improvement of nitrogen operation.Selecting wheat varieties with high nitrogen accumulation before flowering and low nitrogen accumulation at mature stage can increase the nitrogen accumulation in grains and increase nitrogen use efficiency,the distribution of nitrogen and nitrogen in grains of modern varieties is generally higher than that of old varieties in the past.?3?With the increase of nitrogen application,the SPAD value and photosynthesis of winter wheat flag leaves continued to increase.Under the same nitrogen application level,the SPAD value showed fluctuations with the improvement of the variety,modern varieties still maintain a high chlorophyll content in the late filling stage.The net photosynthetic rate of flag leaves in winter wheat at the filling stage showed a gradual increase trend with age,and the net photosynthetic rate of ears in each period showed a gradual increase with age change.Compared with N0 treatment,the net photosynthetic rate of flag leaf increased by9.11%and 18.42%?flowering period?after N120 and N180 treatments,respectively.8.78%and 14.85%?grouting period?.Compared with the old varieties,the photosynthetic rate is maintained at a high level,especially under sufficient nitrogen conditions,Among the ear traits,the modern varieties 2010s,especially the effective spikelet number and grain number,showed excellent traits;after increasing nitrogen,the spike length,awn length,grain number and grain weight of each wheat variety increased.Under the ear-wrapping treatment,the growth of wheat ear length was inhibited,the grain weight of the ears decreased,and the spikelet number and awn length increased.?4?Appropriate amount of nitrogen fertilizer can reduce the photoinhibition of crops under water stress,improve wheat yield-related parameters,biomass,water use efficiency,and increase flag leaf photosynthetic capacity.We conclude that modern varieties can produce higher yields than old varieties under various interactive conditions.In addition,when the nitrogen level is higher,modern wheat varieties are more able to improve flag leaf elongation and photosynthetic rate,and obtain more dry matter,while the old varieties show the opposite law,In addition,the root biomass of modern varieties is relatively reduced,which can accumulate more dry matter in the ground.These results indicate that the nitrogen accumulation,water and nitrogen use efficiency,and partial correlation productivity of modern varieties are higher than those of old varieties in response to water and nitrogen operations.These results show that higher nitrogen fertilizer application cannot significantly improve the nitrogen fertilizer use efficiency of wheat.However,under proper nitrogen application,modern wheat can optimize canopy nitrogen distribution,increase flag leaf and ear photosynthetic energy,and increase photosynthesis.Function ability,enhance plant water and nitrogen utilization efficiency to achieve high yield effect,in particular,it can improve the ability to maintain strong photosynthetic capacity,reduce transpiration rate under drought stress,and ultimately improve water and nitrogen fertilizer use efficiency.Understanding the comprehensive response mechanism to water and nitrogen supply during wheat variety replacement can provide a theoretical basis for improving the fertilizer use efficiency of crops in drylands. |
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