Differences of Photosynthetic Characteristics and Yield Components of Soybean Population at Different Yield Levels

In order to explore the differences of the main yield factors and functional leaf SPAD value, canopy leaf area index（LAI） and light interception rate（LI） of soybean at different yield levels in Anhui Province. In this study, 12 soybean varieties were divided into high yield level, middle yield level and low yield level by the analysis of variance based on yield, and then the yield factors, SPAD value, LAI and LI of the three levels were compared and analyzed.The results show that:（1） The dynamic trends of SPAD value, LI and LAI of soybean varieties at different yield levels showed a single peak curve. However, the decline rates of SPAD value, LI and LAI were different at the later growth stage.The decreasing rate of SPAD value, LI and LAI of high-yield level was lower than that of middle yield level, and the decreasing rate of SPAD value, LI and LAI of middle yield level was lower than that of low yield level.The SPAD value, LI and LAI of high yield level were larger than those of middle yield level, and the middle yield level were larger than those of low yield level.（2） There were no significant differences in 100-seed weight and pod number per plant among soybean varieties at different yield levels.But the seeds number per plant of high yield level was greater than that of middle yield level, and the seeds number per plant of middle yield level was greater than that of low yield level.（3） The yield components and SPAD value, LAI and LI index ranges of high-yield level were proved to be: The SPAD value, LAI and LI were 37.4-38.1, 3.0-3.1 and 81.5%-91.2% during the whole growth period, respectively.The slow leaf senescence, high SPAD value, high LAI and LI, and high photosynthetic capacity in the late growth period were identified as the main physiological basis for high yield.