Studying on Diurnal Variation of Main Photosynthetic Index of Different Soybean Varieties

To investigate the differences between the photosynthetic characteristics of different soybean varieties,diurnal variation of main photosynthetic index was determined for five different soybean varieties by using LI-Cor 6400 portable photosynthesis system in the field condition at flowering and podding stage.And the content of chlorophyll was also determined.The results showed:At flowering stage,net photosynthetic rate and transpiration rate showed a typical bimodal curve,peaking at 10:00 and 15:00;At podding stage,the transpiration rate represented a typical diauxie curve,which reached its highest peak ahead of 2 h,however,the net photosynthetic rate was characterized by a unimodal curve with a peak at 10:00;The highest stomatal conduc-tance was in the morning,and changed slowly after 9:00;Intercellular CO2 concentration was higher in the morning and evening,with little change between 9:00 and 16:00;The SPAD Value of different soybean varieties had no significant difference at flowering stage,and Zhongdou No.8 was significantly lower than the other varieties at podding stage.The study showed that the diurnal variation of photosynthetic index had its regularity among five soybean varieties.It was concluded that the selecting of soybean varieties with high photosynthetic efficiency should take into account of various indicators of photosynthetic characteristics.