| Study on physiological characteristics had paid more and more attention to the process of improvement and yielding cultivated from soybean varieties. These studies not only revealed regular pattern in evolution of soybean shape at beginning of the 20 th century in northern China a spring beans cooked ecological zones(I zone),but provided useful insights for improving soybean varieties and high yield. However, much researches were focused on horizontal comparison in different varieties at the same period or different organs of same varieties, and these researches were focused on agronomic and morphological traits. While researches on physiological characteristics of longitudinal in long-term inter-species during genetic improvement were little, and these were in the initial stage. Especially researches on changes in leaves area and photosynthetic rate of different soybean varieties at different nodes at different stage were little, especially during genetic improvement. Therefore, the changes in physiological characteristics of different soybean varieties released in different eras were compared and analyzed, we aimed to provide reference for improving soybean varieties. In this study, two old soybean varieties(Yuanbaojin and Jinyuan No.1) which were bred in 1929 and 1941 respectively in Jilin province and two new soybean varieties(Jinong No.7 and Jinong No.45) which were bred in 1999 and 2000 respectively in Jilin province, the four soybean varieties were used as materials to study the changes in leaf photosynthetic characteristics and leaves area at different nodes in different stages under same cultivation management mode.The results were showed that differences in leaves physiological characteristics of different soybean varieties were existed at different nodes in different stage.1) Net photosynthetic rate of new soybean varieties were significantly higher than that of old varieties. Net photosynthetic rate of new soybean varieties were higher than that of old soybean varieties at reproductive growth stage in each node of each period. Net photosynthetic rate of old and new soybean varieties were increased at R2 stage at upper. The net photosynthetic rate was reached its peak at R4 stage. Differences of net photosynthetic rate between the old and new soybean cultivars was also maximum at R4 stage. It was a common feature of old and new varieties that net photosynthetic rate showed higher in middle and upper node. At R6 stage, net photosynthetic rate of new and old varieties were declined rapidly, but speed of net photosynthetic rate of new varieties was lower than that of old varieties. It indicated that the stage of photosynthesis of new varieties were longer, and synthesis and accumulation of organic matter of new varieties were better than that of old varieties. These were the reasons of differences for yield formation.2) An increasing trend was showed in the stomatal conductance(Gs) of new varieties. Gs of new and old soybean cultivars were increased from the beginning of R2 stage to R4 stage, and they were decreased from R4 stage. The maximum of Gs were showed in R4 stage. Gs of new varieties were higher than that of old soybean cultivars at R2 and R6 stage. But at R6 stage, Gs of old varieties were higher than that of new varieties. This indicated that the respiration of soybean varieties which were bred in earlier period were stronger at R4 stage, and this was affected the accumulation in dry matter at R4 stage. Gs of new varieties were higher than that of old varieties at R6 stage. It indicated that transpiration of leaf transpiration of new varieties were accelerated to transfer the organic material quickly, and this promoted gain of grain weight. And it was important for increasing of production.3) The increase of leaf area of new varieties was faster than that of old varieties in the early stages of the reproductive growth. The leaf area of new soybean varieties showed slower growth at seeding stage, and growth was accelerated in the early reproductive growth stages, and then stabilized at late stage again. The growth of leaf area showed "slow-fast-slow" growth characteristics. This characteristics contributed to protect the population structure and kept it more reasonable and then extended the duration of leaf function. It indicated that the coordination between photosynthetic performance and leaf area development dynamic was the main reasons for high-yielding of new varieties. Leaves area of lower canopy of new varieties was less than that of old varieties. But leaves area of central node was significantly greater than that of old soybean varieties. At R2 stage, leaves area of both the old and new varieties were increased rapidly. The average leaves area of lower, central and upper node of new varieties were higher than that of old varieties. With the growth of leaves, leaves area of new varieties tended to grow slowly. At the R4 stage, leaves area of lower, central and upper node of old varieties were higher than that of new varieties, and mainly the leaves area of upper node was significantly greater than that of new varieties. Leaves area of old varieties reached a maximum during R4 stage, and then they entered a phase which declined rapidly, and then they entered into R6 stage. At R6 stage, significantly different changes of leaves area were between new and old soybean cultivars of different nodes. Leaves area of new soybean varieties remained unchanged, while leaves of older varieties had begun to aging and falling. Leaves of lower node littered seriously, and leaves area plummeted seriously. New soybeans varieties could remain greater leaves area and higher leaf area index(LAI) at R6 stage, and it indicated that leaves photosynthesis could conduct normally at this stage to synthetic organic compounds and transport and store into the grain. This increased grain weight to ensure high yield.4) The water use efficiency(WUE) of new soybean cultivars had more advantages. The water use efficiency(WUE) of new soybean cultivars and old soybean cultivars kept increasing along with growth stage from R2 stage. The maximum was in R4 stage of all soybean cultivars and water use efficiency then began to decline. WUE of new varieties was higher than that of old varieties at R2, R4 and R6 stage. In general, plants with higher WUE was contributed to accumulate certain dry matter under water stress, and it was important for the formation of production.5) Changes in soybean single leaf transpiration rate is to reach the maximum from flowering; decreases rapidly from pod stage to yellow leaves period. Our results also proved this point. From the point of view at different growth stages, the R2 of contemporary soybean varieties Tr higher than early soybean varieties, and R4 is an early soybean varieties of contemporary higher soybean varieties; to R6 of contemporary soybean varieties Tr on the rise again, the early soybean varieties Tr decreased, contemporary soybean varieties was higher than the early soybean varieties.6) Positive correlation was between different net photosynthetic rate and leaf area of soybean cultivars which were bred in different periods in different nodes at different stages, but it didn’t reach significant levels. |
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