Studies On Photosynthetic Property During Evolutional Succession Of Spring Wheat Varieties In Irrigation District Of Ningxia

Under the field conditions, the evolutionary changes oi photosynthetic property of spring wheat varieties are studied in irrigation district of Ningxia recent 50 years. The research results are shown as follow: 1 Photosynthetic rate of simple leafThere are significant differences on the photosynthetic rate(Pn) of different sites leaves when separated dominant planting varieties of spring wheat of Ningxia recent 50 years. The results showed that the highest Pn exists in flag leaf, and then comes the second reverse leaf, and the third reverse leaf has the lowest rate. It is also shown that during evolutional succession of spring wheat varieties, the photosynthetic rate has a trend to decrease in flag leaf, whereias it decreases in the second reverse leaf, which the factors by non-stomatal limitations are increased.The reactions toward the light at different growth duration are different when different spring wheat varieties planted at various years are concerned. That is, both mooting stage and grain filling stage have higher requirement for the light, on the contrary, anthesis has lower requirement. During evolutional succession of sping wheat varieties, light saturation point gives a trend to decrease, but other indexes, such as the increase of light compensation point and the respiiation rate, and the decrease of maximum photosynthetic rate(PNmax), change in discipline.The Pn of Ningxia Plain spring wheat shows two-peaks with the growth and development of the plant. The first peak appears at the booting stage, and the second one appears at the initial grain filling stage. Along with the varieties alternations, the average photosynthetic rate decreases first then increases, while other indexes, such as PAD(photosynthetic active deration), the content of chlorophyll, the functional duration of flag leaf, LSC(leaf source capacity) of flag leaf increase significantly. Path analysis shows that the most important factor that influences the LSC is the leaf area,' and then the PNmax, the third important factor is the PAD. In conclusion, before heading period, the mainly limitation on photosynthetic rate by CO2 supply was resulted from non-stomatal limitations, but after heading period, stomatal limitation increases and at the late grain filling stage, non-stomatal limitation increases again.Studies on diurnal changes of net photosynthetic rate during evolutional succession of spring wheat varieties shows that in Ningxia plain, the noon nap phenomenon of Pn of modern varieties were alleviated obviously than the local varieties. The Pn diurnal changes at booting stage of Ningchun No.4 and the second time dominant breed is single peak curve, the peaked values reached at 11:00; on the contrary, the photosynthesis of the other old-time dominant varieties have obvious noon nap phenomena, and the diural changes of Pn show two-peaked curve,the peaked value; reached at 11:00 and 16:00. The anthesis of Beituzi is single peak curve, the peaked values reached at 13:00; the other varieties diumal changes of Pn are two peaked curve , the peaked values reached of anthesis reached at 12:00 and 14:00. the average diurnal Pn of modern varieties increased slightly, but area of leaf and LSC heighten obviously. This is indicated that ability of capturing light in modern varieties was raised, and the Pn increases also.Along with the canopy height reduces, there have a bt of changes in the plant. Such as, thePAR(photosynthetically active radiation) reduces, the transpiration rate decreases, the intercellar CO? concentration(Ci) increases, the photosynthetic rate decreases and the non-stomatal limitation increases. Along with the evolutional succession of spring wheat varieties, the transpiration rate at different canopy increases, both stomatal conductance and the intercellar CC>2 concentration increases, the limitation value of stoma decreases first then increases, the light intercept and capture increases but light transmission rate decreases, the extinction coefficient decreases, which induces a decreasing trend of Pn along wi...