Effects Of CO₂ Concentration And Nitrogen Application On Grain Yield, Quality Formation And Their Physiology Mechanism In Winter Wheat

The CO2 concentration in free air is one of the main factors which influence crop production. The IPCC (2007) pointed out that global CO2 concentration would continues to rise in the future and predict this would lead to global warming. Grain yield and quality formation is closely related to C/N metabolic balance in plant, and would regulation and control by the external environment and cultivation measures. CO2 concentration and nitrogen application are main ecological factors affecting formation of wheat yield and quality. Therefore, clarify the effect of CO2 concentration, nitrogen application and interaction on wheat grain yield, quality formation and their physiology mechanism; provide a theoretical basis for establish affects of CO2 concentration on wheat production and to take reasonable regulation and control measures. The free-air carbon dioxide enrichment (FACE) platform was applied to study the effects of increasing atmospheric CO2 concentration and nitrogen application on wheat flag leaf photosynthetic characters, carbon/nitrogen accumulation, translocation, grain quality. And the physiological regulatory mechanisms of CO2 concentration and nitrogen application on wheat grain yield and quality formation were elucidated. Experiment was conducted on FACE platform of Jiangdu in Jiangsu Province, using medium-gluten variety Yangmai 14. Split-plot design was employed in the experiment, the main treatment was CO2 concentration including two levels,379μl·L-1 (Ambient CO2 concentration) and 570μl·L-1(FACE CO2 concentration). The subplot treatment was nitrogen level treatment including two levels,150kg·hm-2(low level, LN) and 250kg·hm-2 (high level, HN).The main results were as follow:1. The grain yield, spike number, grain number per spike and biomass of wheat significantly increased under elevated CO2 concentrations and high nitrogen application. The translocation amount of pre-anthesis assimilate(TAA) and translocation rate of pre-anthesis assimilate(TAR) increased under elevated CO2 concentration and high nitrogen, and significantly increased post-anthesis assimilates accumulation(PAA) and contribution of post-anthesis translocated assimilate to grain(CTA).The translocation amount of pre-anthesis assimilate(TAA) and translocation rate of pre-anthesis assimilate(TAR) were significantly related to yield. The contents of protein, gliadin. gluteinin, glutein of grains and sedimentation value of flours were significantly reduced, and the contents of starch and its components significantly increased under elevated CO2 concentration, while inverse under nitrogen fertilization. The dough stability time and viscosity characteristics, such as peak viscosity, final viscosity and setback value, increased significantly under elevated CO2 concentration and high nitrogen application. In addition, the interaction of CO2 concentration and nitrogen application had significant positive effects on grain yield and biomass, while no effects on grain qualities. Therefore, with elevated CO2 concentration in the future, increasing nitrogen application would be favorable for improving grain yield and paste characteristics, combining with high grain quality in wheat.2. Flag leaves Pn in early and middle stage of filling was increased under elevated CO2 concentration, Pn and SPAD value were accelerate dropped in late filling stage. Flag leaves Pn was increased under high nitrogen application.The Gs was decreased and Ci was increased by elevated CO2 concentration. Nitrogen application and CO2 concentration have the opposite effect. The Fo, Fv/Fm, Qp in flag leaf were decreased, NPQ were increased, OPSⅡelectron transport activity were decreased under elevated CO2 concentration, large amounts of light energy dissipation in the form of heat energy. Nitrogen application and CO2 concentration have the opposite effect. It also maintain chlorophyll fluorescence reaction center highly open, relieve Pn decrease in flag leaf.3. The sucrose phosphate synthase (SPS), sucrose synthase (SS), free bound starch synthase (SSS), bound starch synthase (GBSS) activity were increased by CO2 concentration and nitrogen application. It also increased grain starch accumulation rate. The grain starch content was also improved by CO2 concentration. CO2 concentration and nitrogen application increased sucrose synthesis capacity of flag leaf and improve sufficient substrate for starch synthesis in grain, higher grain SS, SSS, GBSS activity provide enzymatic protection for increase starch content in grain.4. Nitrate reductase (NR) activity, glutamine synthease (GS) activity, free amino acid content in flag leaf was decreased by CO2 concentration. And resulting in free amino acid which transport from flag leaf to grain decreased. It also decreased glutamine synthease (GS) and glutamic pyruvic transaminase (GPT) activity in grain, decreased protein accumulation rate, and resulting in grain protein content decreased. Each key regulatory enzymes activities in flag leaf and grain increase by nitrogen application, thus increased protein content in grain. Therefore, with elevated CO2 concentration in the future, increasing nitrogen application would be favorable for relieving grain protein content decrease.5. The dry masses of flag leaf and stem were increased under elevated CO2 concentration and high nitrogen application. N content were decreased under elevated CO2 concentration, and high nitrogen application have the opposite effect. The translocation amount of pre-anthesis assimilate (TAA) and translocation rate of pre-anthesis assimilate (TAR) was increased under elevated CO2 concentration and high nitrogen application. It also increased post-anthesis assimilates accumulation (PAA) and contribution of post-anthesis translocated assimilate to grain (CTA). The nitrogen translocation amount of pre-anthesis assimilate (NTAA) in each nutrition was decreased and nitrogen translocation rate of pre-anthesis assimilate (NTAR) in each nutrition was increased under elevated CO2 concentration.The nitrogen translocation rate of pre-anthesis assimilate (NTAR) was increased and nitrogen translocation amount of pre-anthesis assimilate (NTAR) was decreased under high nitrogen application. The nitrogen post-anthesis assimilates accumulation (NPAA) was increased and nitrogen contribution of post-anthesis assimilate to grain nitrogen (NCTA) was decreased under elevated CO2 concentration and high nitrogen application. The grain starch yield was significantly related to translocation amount of pre-anthesis assimilate (TAA) and post-anthesis assimilates accumulation (PAA). The grain protein yield was significantly related to nitrogen translocation amount of pre-anthesis assimilate (NTAA) and nitrogen post-anthesis assimilates accumulation (NCTA).