Effects Of Nitrogen Fertilizer Application Regimes On Carbon And Nitrogen Metabolism, Grain Yield And Quality Of Two Spike-Type Super-High-Yield Wheat (Triticum Aestivum L.) Cultivars

The metabolisms of carbon and nitrogen are two basic physiological processes in the wheat plant,which have significant effects on grain yield and quality.Application of nitrogen fertilizer is one of the best ways to increase grain yield and quality of winter wheat. In this paper,a series of pot and field experiments using a multi-spikelet cultivar, Yumai49-198,and a big-spikelet cultivar,Lankao Aizao8,were carried out to estimate effects of nitrogen fertilizer application on characteristics of carbon and nitrogen metabolism.By ¹⁴C and ¹⁵N tracer methods,remobilization of assimilation matter reserved in the plant and ¹⁵N amount absorbed by wheat plant from soil were also studied in the dissertation.The main results are as follows:1 In pot experiments,activities of key photosynthetic enzymes and fluorescence parameters were investigated in different nitrogen treatments.The results indicated that nitrogen application had significant effects on activity of enzyme and fluorescence parameters of photosynthesis in flag leaves of two wheat cultivars.Activities of ribulose 1, 5 bisphosphate carboxylase(RuBPC),phosphoenolpyruvate carboxylase(PEPC)and glycollie oxidase(GO)in flag leaves decreased with flag leaf senescence.Activities of photosynthetic enzymes in flag leaves also increased with nitrogen fertilizer application rate,and the maximum activity of RuBPC and PEPC with treatment N4(4.80 g N plot^-1) and N3(3.60 g N plot^-1),respectively.Activities of RUBPC,PEPC and GO in flag leaves increased with delaying of nitrogen fertilizer application time,and the stronger activities of enzyme with either treatment Nc(topdressing N at jointing stage)or Nd(topdressing N at heading stage).In addition,Activities of photosynthetic enzymes in flag leaves of the big spikelet cultivar were stronger than those of the multiple spikelet cultivar in late flag leaf senescence.Fluorescence parameters,Fv/Fo,Fv/Fm,increased with either increasing in nitrogen fertilizer application rates or delaying of nitrogen fertilizer application time. Correlation analyses showed that there was a positive correlation between activities of enzymes and grains weight per ear.2 Effects of nitrogen fertilizer application rate on activity of key enzymes in sucrose metabolism were also studied.The results showed that activities of SPS and SS in flag leaves and grain presented a single-peak curve during grain filling,and the peak value appeared at 15-20 days after anthesis(DAA).Changes of content of soluble sugars and sucrose were observed during grain filling as well.Activity of SPS and SS in flag leaves and grain increased with nitrogen fertilizer application rate in treatment N3.Contents of soluble sugar and sucrose increased with nitrogen application rate,and the maximum content were also recorded in treatment N3.The results also suggested that optimal nitrogen application rate would lead to increase the activity of enzyme involved in sugar metabolism and sugar content,which benefit ed the increase of grain weight.3 Effects of different nitrogen fertilizer application rates and dates on activity of key enzymes involve in starch synthesis were also studied.The results showed that activities of ADPG-PPase,SSS,SBE and GBSS in grains presented a single-peak curve during grain filling,and the maximum activities were recorded at 25 DAA.Activity of ADPG-PPase, SSS,SBE and GBSS increased with nitrogen fertilizer application rates,but excessive nitrogen application might decrease activities of enzymes.Activities of enzymes increased with the delaying of nitrogen application time.Correlation analyses also showed that activities of key enzymes involved in starch synthesis were positively correlated to amounts and speed of starch accumulation.And the concentration of amylose,amylopectin and total starch in grains increased with nitrogen application rate,indicating that optimal nitrogen application would increase grain weight and yield.4 Effects of different nitrogen fertilizer application rate and dates on activity key enzymes involved in nitrogen metabolism were studied.The results indicated that activity of NR,GS and GOGAT increased with nitrogen application rate,and the maximum activity was recorded in treatment N3 or N4.With the delaying of nitrogen application time, activity of enzymes increased and the highest of activity appeared in treatments with nitrogen topdressed either at jointing stage or heading stage.In general,grain protein concentration was enhanced with the increase of nitrogen rate and delaying of applied time for both cultivars.These results indicated that the increase of activity of the enzyme in nitrogen metabolism would benefit accumulation of grain protein and increase of grain yield.5 The pot experiments were conducted to study effects of nitrogen applcation at different developmental stages on uptake,translocation and partitoning of nitrogen in two different spike-type cultivars.The results showed that grains had the highest nitrogen content among different in plant organs at maturity,next were roots＞glumes and rachis＞stems and leaf sheaths＞leaves.Partitioning proportion of nitrogen aamong different plant organs was: grains＞stems and leaf sheaths and leaves＞glumes and rachis(roots).Moreover, accumulation of nitrogen in grains increased with the delaying of nitrogen application time, and the maximum value was observed in treatments with nitrogen top-dressed at jointing stage.The results also showed that nitrogen accumulation from top-dressed nitrogen fertilizer accounted for 16.45～26.6%of the total.With delaying of topdressing nitrogen time,nitrogen accumulation from top-dressed fertilizer increased,and the maximum value appeared with Lankao Aizao 8 in treatment Nb(nitrogen was applied at reviving stage)and with Yumai 49-198 in treatment Nc(nitrogen was applied at jointing stage),respectively.With the development of grain filling,nitrogen in wheat plant was translocated from vegetative organs to grains.The ratio of ¹⁵N/N decreased from 0 to 20 DAA,while 20 to 30DAA the ratio keep constant.These results indicated that the grain nitrogen partitioning from top-dressed nitrogen was higher than that from soil and basic fertilizer in the early grain filling period.The assimilated nitrogen after anthesis and the contribution of nitrogen assimilation to grains after anthesis increased with delaying of nitrogen application date,while the contribution of reserved nitrogen pre-anthesis decreased. The contribution of pre-anthesis total nitrogen to grain nitrogen accumulation was higher than that of nitrogen assimilation post-anthesis.The wheat grain yield and protein yield increased with delaying nitrogen fertilizer application time,and the maximum value was recorded when nitrogen was applied at jointing stage.6 Effects of nitrogen application rates on partitioning of assimilated carbon in different plant organs was studied by ¹⁴C tracer method in the pot experiment.The results indicated that stems and leaf sheaths accounted for the highest partitioning percentage of assimilated ¹⁴C at maturity,next was grains＞glumes and rachis＞leaves.In comparison, higher nitrogen application rate reduced the ¹⁴C transportations into the stems and sheaths, but increased the ¹⁴C reallocation into grains.The partitioning percentage of ¹⁴C assimilated in stems and sheaths of Lankao Aizao 8 was higher than that in Yumai 49-198, indicating that there might be more carbon assimilation in stems and leaf sheaths and leaves of the big-spike type wheat cultivar.Accumulation of ¹⁴C in grains per stem increased with the development of grain filling,but decreased near maturity.Comparatively,¹⁴C accumulation in grains were higher when nitrogen application rate was lower.There was 34.94%of the assimilated in grains derived from reserved pre-anthesis assimilates and there was 65.06%from post- anthesis photosynthesis.Moreover,translocation amount and proportion of reserves,and contribution of assimilates pre-anthesis to grains decreased with nitrogen application rate.However,contribution of assimilates post-anthesis to grains and grains weight per stem increased with nitrogen application rate.The results also showed that the contribution ratio of post-anthesis assimilation to grains was 77.84%and 56.29%for Lankao Aizao 8 and Yumai 49-198,respectively,indicating that Lankao Aizao 8 had more post-anthesis assimilation than Yumai49-198.In comparison,higher nitrogen application rate enhanced fertile spikelets per spike and reduced the of sterile spikelets. Finally,grain yield in treatment with high nitrogen application was higher than that with lower nitrogen applications.Meanwhile,increase in of grain yield of Lankao Aizao 8 in treatments of T2 and T1 was higher than that of Yumai 49-198,indicating that nitrogen fertilizer has significant effects on Lankao Aizao 8 than Yumai 49-198.7 In the field experiments,effects of nitrogen fertilizer application rates and dates on color of flour,the quality of noodle were studied for those two cultivars.The results showed that redness(a^*),yellowness(b^*)of flour and paste increased while brightness(L^*) declined when nitrogen application rate was increased.The highest value of L^* was obtained in treatment NO(0 g N ha^-1),and the highest values of a^* and b^* were observed in treatment of N180 or N270((180kg N·ha^-1,270kg N·ha^-1),In addition,brightness(L^*) of flour decreased with delaying of nitrogen application time,but a^* and b^* of flour increased,a^* and b^* of noodle sheet increased,while L^* value decreased with the elongation of rest time.The texture analysis showed that hardness,gumminess and chewiness enhanced with the increase in nitrogen application rate.Score of noodle evaluation increased with lower nitrogen application rate to some extent,but decreased with further increase in nitrogen application rate.The results also indicated that texture traits and sensory evaluation together could be used to evaluate noodle sensory characteristics.