| To understand the responses and physiological mechanisms of soil fertility during wheat genetic improvement in Shaanxi Guanzhong Plain in order to offer a standard reference for the future wheat breeding,this study investigated the response of winter wheat grain yield,yield components,dynamic of wheat growth,nutrient uptake and translocation and nutrient use efficiency to different soil fertility levels which were established by long-term fertilizer experiments.Field experiments were conducted from 2013 to 2015 with five milestone wheat varieties released between 1970 and 2005 combined with 11 nutrient or water input levels?9nutrient treatments under irrigation and 2 nutrient treatments in rainfed condition?.The main results were summarized as follows:Wheat grain yield ranged from 0.9 t ha-1 to 8.3 t ha-1,biomass ranged from 2.3 to 18.2 t ha-1,and harvest index ranged from 0.33 to 0.49 under experimental conditions.In both seasons,yield responded to all three sources of variation,treatment?T?,variety?V?and their interaction?T×V??all P<0.0001?.Biomass responded to treatment and interaction between treatment and variety.Harvest index responded to variety and interaction between treatment and variety.Plasticity of yield increased with year of cultivar release,reflecting the enhanced ability of newer varieties to capture the benefits of higher inputs.Plasticity of harvest index declined with year of release,highlighting the stability of harvest index of newer varieties compared to their older counterparts.All yield components responded to treatment and variety,except a lack of variety effect in spike number in season 2014-2015.Interaction between treatment and variety was not always detected in both seasons.However,wheat selection for yield improved grain number and annual rate of increase between 1970 and 2005 was 1.15·106 ha-1.Genetic improvement also increased the plasticity of grain number,but no significant changes in plasticity of grain number per spike and spike number were observed.A non-linear model with an inflection point at 1989 highlighted two phases in the time trend of grain weight:it decreased between1970 and 1989 with an annual rate of 0.72 mg and increased afterwards with an annual rate of0.68 mg.No significant trend was detected in grain weight during wheat genetic improvement.Grain filling rate increased at first and then decreased afterwards during wheat selection,and the inflection point was at 1988,which suggested the wheat variety released after 1980with a higher grain weight was mainly associated with the enhancement of grain filling rate.Water-soluble carbohydrate?WSC?translocation amount and rate showed a non-linear trend during wheat selection for yield,and it decreased at first and increased afterwards.Furthermore,the translocation amount of WSC was mainly attributed to the stem WSC translocation.During wheat genetic improvement,water-soluble carbohydrate concentration in stem and spike showed quadratic trend with the inflection point in 1982 and 1985,respectively.At the same time,shoot biomass at anthesis had a similar quadratic trend,so did the stem and spike biomass at anthesis,and all their inflection point was beyond 1980.These results indicated that the enhanced grain yield and grain weight in wheat varieties released after 1980 were due to the improvement in shoot biomass?main including stem and spike?and WSC.Leaf area index?LAI?showed a non-linear trend during wheat selection for yield,and it increased from 1983 to 2005 with a linear rate of 0.032 year-1.The ratio between LAI and grain number per unit area decreased between 1970 and 1997 and stabilized afterwards.Maximum SPAD value changed non-linearly during genetic improvement with an inflection point in 1986,which was emphasized two phases in the time trend of SPAD:it decreased between 1970 and 1986 and increased afterwards,at the same time,LAI×SPAD increased after 1983,which indicated breeding had improved the source strength in modern wheat variety.During wheat selection for yield,malondialdehyde?MDA?constant k decreased significantly,while the doubling time increased significantly;soluble protein decreasing rate decreased firstly and increased subsequently.In addition,genetic improvement in wheat have significantly increased photosynthetic rate?Pn?,transpiration rate?Tr?and stoma conductance?Gs?in flag leaf at grain filling stage.Therefore,during the grain filling stage,wheat breeding progress enhanced the photosynthesis rates,however,leaf senescence progress was accelerated.The result of principle component analysis?PCA?indicated that,under different water and nutrient input environments,grain yield had highly correlation with photosynthesis traits?Pn,Tr and Gs?after anthesis.During wheat genetic improvement,grain yield increased at a rate of 0.46%per year with no apparent increase in the uptake of nutrients.Nitrogen harvest index did not change,phosphorus harvest index,however,increased at a rate of 0.15%per year.As a consequence,yield per unit nitrogen uptake and yield per unit phosphorus uptake increased at similar rates?0.4%per year?at the expense of nutrient concentration in grain,which declined at a rate of0.47%per year for N and 0.31%per year for phosphorus.No trends in nitrogen nutrition index were found.In conclusion,our study demonstrates the synergy between breeding and agronomy whereby selection for yield has improved the ability of winter wheat to capture the benefits of higher inputs that has been a major feature in Shaanxi Guanzhong Plain over the last six decades.In addition,grain number and it's plasticity were improved simultaneously during this progress.Further gains in yield need to be matched by increasing nitrogen uptake to maintain grain protein.Dilution of phosphorus in grain needs to consider the putatively of phytate for human nutrition,and the need for phosphorus reserves in seed for crop establishment. |
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