Agricultural Properties And Photosynthetic Characteristics Of Winter Wheat Cultivars Released In Different Years

17 winter wheat cultivars (Triticun aestivum L),representatives of those widely cultivated in Beijing over the past five decades,were planted in the same environmental conditions,and improvements in agricultural traits and some photosynthetic characteristics were investigated. Three cultivars,Jingdong 8,Nongda 139 and Yanda 1817 were further selected to study the ecophysiological characteristics associated with increased of grain yield. We also tested responses of gax exchanges to CO2 and photosynthetic photon flux density (PPFD) changed. The experiment was conducted in the Experiment Farmland of Beijing Academy of Agro-forestry (3909'N,11604'E) in 1999-2001. Results are shown as followings.1. Some agricultural traits were changed during the improvement process of wheat cultivars grain yield. For example,harvest index (HI) and 1000 grain weight were increased,and biomass yield,plant height,ear number and grain yield per plant and ear length were decreased. Grain yield was positively correlative with grain weight per ear,1000 grain weight,HI,and negatively correlative with plant height,ear number. It was also found that plant height was positively correlative with ear length,grain yield and ear number per plant,and negatively correlative with HI,and 1000 grain weight. HI was positively correlative with 1000 grain weight,and negatively correlative with ear number. It suggested that decrease in plant height,improvement in HI and 1000 grain weight contributed to increase in grain yield during improvement process of wheat cultivars.2.From seedling to middle stem elongation stage,net photosynthetic rate (PN),stomatal conductance (gs),transpiration rate (E),Fv/Fm of different wheat cultivars tended to increase with years of released,but water use efficiency (WUE) decreased. PN and E were greatly positively corrective with yield from seedling to booting stages. Gs was significantly positively correlative with yield stem elongation and booting stages (R=0.616,0.499,P<0.05). Fv/Fm were significantly positively correlative with yield at seedling and middle stem elongation stages (P<0.05) . However,WUE was distinctly negatively correlative with yield at seedling,stem elongation,middle stemelongation,anthesis and mature stages (P<0.05,P<0.001) . Thereby,not only net photosynthetic rate was improved during improvement of wheat cultivars,but also chlorophyll fluorescence Fv/Fm was improved. Which means that the photochemical yield of PSII was improved.3. Flag leaves of Jingdong 8 with the highest yield remained the highest net photosynthetic rate (PN),transpiration Rate (E)> stoma conductance,potorespiration rate,chlorophyll content,water content,and lowest dark respiration among the three cultivars from booting to grain filling stage. And daily changes of PN in flag leaves of Jingdong 8 remained highest at middle stem elongation stage,and the difference became less obvious as the wheat developing. Usually,it was higher than that of the other two cutivars,in earliy morning,and lower at noon and afternoon than that of Yanda 1817. Difference in Fv/Fm of different wheat cultivars was similar to PN. However,midday depression of photosynthesis was the smallest in Yanda 1817,which might suggest that Yandal817 was resistant to photoinhibition at some degree. We further studied relationship between source and seek,and found that Jingdong 8 kept a better balance between source and pool,and has a highest HI,grain weight per ear and 1000 grain weight than the other two cultivars. We concluded that improvement in yield of wheat cultivars not only owned to the higher efficiency of photosynthesis,but also owned to lower dark respiration and a better balance between source and seek.4. Net photosynthetic rate per unit leaf area,and water use efficiency (WUE) of flag leaves increased with the elevated CO2 concentration. PN and WUE of Jingdong 8 increased by 173 % and 81 %,while those of Nongda 139 and Yanda 1817 increased by 88 % and 66 %,76 %and 65 %,respectively,as CO2 concentration increased from 360 to 720 umol mol-1. Jingd...