Study On Gas Exchange Characteristics Of Leaves Of Hybrid Soybean

With the hybrid soybean variety zajiaodou 2 and zajiaodou 5 as test material, Using the LI-6400 type of portable photosynthesis system measures leaf gas exchange characteristics、light response characteristics、the daily variation characteristics according to the change of growth stage under the field conditions. The results showed as follows:Leaf net photosynthetic rate(Pn) and apparent mesophyll conductance(Pn/Ci) of hybrid soybean emerge single peak curve during the growth variation. From V4 phase to R4 phase, Pn and Pn/Ci of leaf increased, R4 stage was the highest, and then decreased gradually, R7 minimum. Stomatal conductance(Gs) and transpiration rate(Tr) varied with the hybrid soybean variety development stages, contents in the leaves of Gs and Tr decreased gradually, atthe V4 stage was the highest, the lowest R7 stage. The leaf intercellular CO2 concentration(Ci) with the growth stage of changes express the higher lever at the V4 and R7 stages, relatively the lower lever at the R2,R4 and R6. The leaf water use efficiency(WEU) varied with the hybrid soybean variety development stages, the WEU of leaf increased gradually between the V4 phase to the R7 phase, and the lowest contents at the V4 phase, the highest contents at the R7 phase.Diurnal variation of hybrid soybean leaf Pn, WEU and Pn/Ci at the pod filling stage showed the change rule of the bimodal curve. The emergence of midday depression in the noon morning peak appeared at 10:00, afternoon peak appeared at 15:00,and peak value in the morning higher than peak value in the afternoon. The Gs of leaf blade decrease gradually with the advance of time, it was maximum at 6:00 in the morning and minimum at 18:00 in the afternoon. The diurnal variation of leaf Ci showed that at the 6:00 in the morning achieves the highest peak and at the 18:00 in the afternoon achieves the second peak. At 6:00 to 9:00, the Ci of leaf ripid decrease. At 9:00 to 16:00, the Ci of leaf has a little change. At 16:00 to 18:00,the Ci of leaf increase significantly. The Tr of leaf blade express a single peak curve, the peak value appeared at the 12:00.When the light response represented as PAR<200 μmol?m-2?s-1, the leaf Pn of hybrid soybean Increases in a linear with the PAR increasing, while PAR was between 200 to 800 μmol?m-2?s-1,the leaf Pn of hybrid soybean ripid increase with the PAR increasing. When the PAR was continuously enhanced, the leaf Pn increased slowly, and light saturation point and light compensation point respectively was 1200 μmol?m-2?s-1 and 65 μmol?m-2?s-1. Leaf blade Gs on light response was consistent with the Pn findings.