| As a good"medicine and food homology"crop,common buckwheat grains are rich in protein,starch,flavonoids,amino acids,vitamins and minerals,and have high nutritional value.With the improvement of people’s living standards,the demand of common buckwheat is increasing.Nitrogen,as an important nutrient element,could affect the yield and quality of crops.However,there are few reports about the effects of nitrogen fertilizer on the yield and quality of common buckwheat at present.Therefore,four nitrogen fertilizer levels of 0 kg/hm~2(N0),90 kg/hm~2(N1),180 kg/hm~2(N2)and 270 kg/hm~2(N3)were set to study the endosperm development process,starch accumulation,activities of key enzymes for starch synthesis,starch physicochemical properties,agronomic traits and yield in two years.The main results were as flows:(1)The application of nitrogen fertilizer significantly promoted the degradation of chlorophyll in the seeds of common buckwheat and made the seeds darker.The length,width and thickness of common buckwheat grains increased rapidly with the growth process,and tended to be stable at the later growth stage,and the length,width and thickness of grains first increased and then decreased with the increase of nitrogen application rate.The amyloplasts in the endosperm cells were accumulated from the edge to the center,and the number of endosperm cells significantly increased after the application of nitrogen fertilizer,and the peak value appeared under N2 treatment.(2)The application of nitrogen fertilizer could affect the starch accumulation of common buckwheat grains.The starch content and starch accumulation rate of two varieties under different nitrogen fertilizer levels were significantly different.The contents of amylose,amylopectin and total starch in Xinong 9976 and Beizaosheng grains had the highest values at the N2 level,and the accumulation rate of amylose,amylopectin and total starch all show a unimodal curve change,and increased first and then decreased with the extension of flowering time with the maximum showing on the15 th day after flowering.Comparing the two common buckwheat varieties,the contents and accumulation rate of amylose,amylopectin and total starch of Xinong9976 were significantly higher than that of Beizaosheng.The application of nitrogen fertilizer could significantly affect the activities of ADP-glucose pyrophosphorylase polypeptide(ADPG-PPase),granule bound starch synthase(GBSS),starch branching enzyme(SBE)and soluble starch synthase(SSS)in common buckwheat grains.The activities of these four key enzymes for starch synthesis all showed a single peak change under different nitrogen fertilizer levels,which first increased and then decreased,and all peaked on the 15 th day after flowering.There were significant differences in the key enzyme activities for starch synthesis of the two common buckwheat varieties,and the key enzyme activity for starch synthesis in Xinong 9976 grains was higher than that of Beizaosheng during the growth period.(3)The application of nitrogen fertilizer could significantly affect the physicochemical properties of common buckwheat starch.With increasing nitrogen levels,the water content significantly decreased,ash content and crude protein content significantly increased,while the amylose content showed a trend of first increasing and then decreasing.The volume distribution,amout distribution,surface distribution and particle size distribution all showed a unimodal distribution,and there were significant differences under different nitrogen levels.The light transmittance,water absorption,oil absorption,water solubility and swelling power of two varieties all first increased and then decreased with increasing nitrogen application,and peaked under N2 treatment.Nitrogen application can not change the granular morphology and crystalline structure of common buckwheat starch,while the order structure obviously reduced.The hardness,springiness,cohesiveness,gumminess,chewiness and resilience significantly decreased by applying nitrogen fertilizer.With the increase of nitrogen application level,the peak viscosity and breakdown viscosity significantly decreased,the through viscosity,final viscosity and setback viscosity first increased and then decreased,while the gelatinization temperature significantly increased.The onset temperature and conclusion temperature first increased and then decreased,while both the peak temperature and gelatinization enthalpy significantly increased with increasing nitrogen application rate,and peaked under N3 treatment.The storage modulus and loss modulus both first increased and then decreased,and peaked under N2 treatment.(4)With increasing nitrogen levels,the plant height,node numbers of main stem,main stem branches number,and flower clusters number all increased first and then decreased.The grain weight per plant of Xinong 9976 peaked under N2 level,while Beizaosheng had the largest value under N3 level.Xinong 9976 had the highest yield in 2019 and 2020 under N2 level,while the yield of Beizaosheng peaked under N3 and N2 levels in both years,respectively,and the yield of Xinong 9976 was significantly higher than Beizaosheng.On the whole,the N2 level(180 kg/hm~2)was more conducive to promote the growth and yield of common buckwheat plants.Therefore,the recommended optimal nitrogen application rate for common buckwheat was 180kg/hm~2 in the actual planting process. |
