Effects Of Elevated CO₂ Concentration And Different Nitrogen Levels On Photosynthetic Characteristics And Yield Components Of Foxtail Millet

Based on the artificial climate control chambers of Shanxi Agricultural University,different nitrogen（N）supply levels（nitrogen deficiency,0g/kg;sufficient nitrogen supply,0.2g/kg）and different CO₂ concentrations（normal CO₂ concentration of 400μmol/mol;elevated CO₂ concentration of 600μmol/mol）were set up in this study.Jingu 21 was used as the experiment material,and were potted in 2018 and 2019 to studyed the effects of elevated CO₂ concentration [CO₂] and N supply on stomatal structure,photosynthetic characteristics,yield components,microelements content and grain yield of foxtail millet plants.The physiological and ecological responsed mechanism of leaf photosynthese and N utilization in response to the increased [CO₂] and N supply was discussed.The results are as follows:（1）At jointing stage,elevated [CO₂] significantly increased the perimeter and area of single stomatal apparatus and decreased the stomatal density of foxtail millet leaves under two nitrogen supply levels.Compared with the condition of N stress,elevated [CO₂] increased the perimeter and area of single stomatal apparatus and decreased the density of stomatal apparatus.At heading stage,elevated CO₂ concentration had no effect on the perimeter of single stomatal apparatus of paraxial and abaxial epidermis of leaves under both N supply,increased the area of single stomatal apparatus and decreased the area of single stomatal apparatus under N supply.N supply had no significant effect on the stomatal density.Therefore,the effect of stomatal apparatus morphological characteristics of foxtail millet leaves is mainly changed in jointing stage,while the change of heading stage is small.（2）At jointing and heading stage,the increased range of leaf area and N condition per unit leaf area（Narea）was greater under the adequate N supply than that under the N stressed.Elevated [CO₂] had no significant effect on specific leaf weight,leaf biomass and nitrogen content per unit biomass（Nmass）under the both nitrogen supply.（3）At jointing and heading stage,elevated [CO₂] significantly increased Pn and WUE of leaves under the condition of sufficient nitrogen supply,but had no significant effect on Pn and WUE under the different N supply.At jointing stage,elevated CO₂ concentration significantly reduced the content of chlorophyll a,b,（a+b）and the energy（ETO/RC and ETO/CSM）used for electron transfer per unit reaction center and per unit cross-sectional area of leaves under N stressed condition,but adequate N supply could alleviate this inhibition.At heading stage,the inhibition of electron transport under elevated [CO₂] was alleviated by number of active reaction centers（RC/CSM）per unit cross-sectional area under nitrogen deficiency.（4）With elevated [CO₂],the activities of GS and NR respectively increased by 67.16%and 18.19% under adequate N condition at jointing stage,but not under N stressed condition.At heading stage,the activity of GS and NR increased by 8.35% and 14.54% respectively with elevated [CO₂].The increase of GS and NR under N stressed condition was smaller than that under N supply adequate.（5）With elevated [CO₂],the Cu and Zn concentration in grains increased significantly under the both N conditions,and trends in the two-year change were similarity,and were not limited by the nitrogen level.Elevated [CO₂] exert no significant effect in grains Mn and Mg concentration under the both N conditions in 2018,but decreased significantly in 2019（Mg concentration only decreased under nitrogen deficiency）.（6）The results of two years’ research showed that elevated [CO₂] could significantly improve the leaf,stem and shoot biomass under both N supply at jointing and heading stage,regadless of N conditions.In the harvest period,elevated CO₂ concentration significantly increased the weight of single spike,the weight of grain per spike,the length and diameter of spike under the both N supply.The length and diameter of spike increased by 9.45%-22.93%and 26.2%-30.94% respectively under the condition of sufficient N supply,and the increase was greater than that under the treatment of nitrogen deficiency.（7）In summary,the stomatal structure,photosynthetic performance,nitrogen metabolism related enzyme activity and grain yield were increased with elevated [CO₂] under N adequate supply,while the nitrogen deficiency reduced the C fixation capacity by reducing stomatal area,leaf area,Narea,chlorophyll content,Pn,ETO/RC,ETO/CSM,GS and NR activity,and then reduced the grain yield under elevated [CO₂].