Comparison of photosynthetic characteristics in the leaves of modern and old soybean cultivars

In order to understand relationship between photosynthetic characteristics and yield,photosynthetic characteristics and yield in four old soybean cultivars[Glycine max(L.)Merr.] and four modern soybean cultivars spanning seven decades were studied.The results showed that the yield of modern cultivars was 91% higher than that of old cultivars.Simultaneously,the net photosynthetic rate(Pn),stomata condutance(Gs),transpiration(Tr),water use efficiency(WUE),chlorophyll content(Chlo) and specific leaf weight(SLW) of modern cultivars were higher than those of old cultivars,the net photosynthetic rate increased most,reached 17.3%.Intercellular CO2 concentration(Ci) in modern cultivars was lower than that in old ones.The yield was significantly positively correlated with the net photosynthetic rate at flowering and seed-podding stage,correlation coefficients of other photosynthetic characteristics and yield was unstable.