Research On Changes Of Photosynthetic Characteristics And Nitrate Reductase Activity From Genetic Improvement Of Jilin Soybean Cultivars

With the genetic improvement in soybean cultivars, selective breeding high production soybeancultivars conformed high-yield structure and function characteristic. Some structure characteristic is choiceresult, but some concealed physiological characteristic hasn't been noted in the choice process. As theimprovement of modern technology, some concealed physiological characteristic may measure using theinstrument surveys definitely. Using modern test analysis technology, we measured and analyzed the netphotosynthetic rate (Pn), stomata conductance (Gs), transpiration (Tr) in the leaves. The expectationprovides the theory basis for the high yield breeding.From 2005 to 2006, the experiment was conducted at experimental station of Jilin AgriculturalUniversity, the results as follows:Yield is a important index of soybean breeding. With the genetic improvement in soybean in Jilinprovince, the yield has increased 1103.7 kg/hm² in the past 82 years from1923—2005, increased 95.94%, or12.5 Kg/hm² year and 0.98% in each year.Leaf area index (LAI) was increased as the genetic improvement of soybean cultivar. LAI was highlysignificantly positive correlated with yield after flowering stage. LAI was parabola condition, which ofsoybean cultivar in 1920s-1940s, 1950s-1960s, 1970s-1980s, 1990s-2000s .There was the largest leaf areaindex at about 70 days after seedling. The LAI of 1990s-2000s breed were higher 15.8%, 12.0% and 8.6%than that of 1920s-1940s, 1950s-1960s, and 1970s-1980s, respectively. The result showed that the LAI ofnew breed rapidly increased, highly maximum, longer and calm the largest LAI, slow wither comparedwith the old breed. It is a main reason of seed yield increasing as the genetic improvement of soybeancultivar.As the increase of yield, harvest index was increase with year of release during the geneticimprovement in soybean cultivars. Harvest index was highly significantly positive correlated with yield.The variation of dry matter accumulation showed that the plant dry matter weight and grain seed dry weightof breeding in different years were increased with the year of release. The plant dry matter weight wasincreased gradually from seedling to middle seed-filling stage (after seedling 90 days). The maximum is atthe middle seed-filling stage, then decline. Dry matter accumulation was increased gradually from beginseed-filling (after seedling 80 days) to end seed-filling stage (after seedling 110 days), the maximum was atthe end seed-filling stage, decline at mature stage. During 40 days from begin seed-filling to endseed-filling stage, the increasing rate of seed dry weight is 4.86,5.95,7.09 and 8.08 g·m^-2.d^-1 in soybean cultivar in 1920s-1940s, 1950s-1960s ,1970s-1980s, respectively. It is one of the important factors ofincreased grain yield, that seed dry weight is rise quick in modern soybean cultivars.The correlation analysis of leaf photosynthetic rate and the breeding year during the five growth stagesshowed that: the leaf photosynthetic rate was highly significantly positive correlation at the seed-poddingstage, and the related coefficient is the highest (r=0.7275^**). Through to five growth stages each parametercomparison and the analysis, we discovered that seed-podding stage is important time of soybean growth. Itwas deciding directly the photosynthesis effective product revolution and assign. At the whole stages,seed-podding stage has the highest net photosynthetic rate, especially the photosynthetic rate of high yieldcultivar breeding after the 1990s-2000s were higher 25.7% than the cultivar of 1920s-1940s at theseed-podding stage. The seed-podding stage is crucial stage that affects the soybean yield.The correlation analysis of leaf photosynthetic rate, Pn/Ci and yield showed that: At the whole growthstages, the leaf net photosynthetic rate, Pn/Ci was highly significantly or significantly positive correlationwith yield. The related coefficient(r=0.4309^*,0.4816^*) is the highest in seedling, and the relatedcoefficient(r=0.6368^**, 0.6502^**) is the highest in seed-podding stage. Pn and Pn/Ci could as physiologicalselection indexes of high yield breed.During the genetic improvement in soybean cultivars, Pn, Gs, Tr, chlorophyll content and SLW isincreasing with year of release. Pn of modern high yield cultivars wasn't only high, but Gs, Tr, chlorophyllcontent and SLW of the close correlation parameter with the yield forms also high. The yield and Pn hadthe most close and stable relationship in all of index. Therefore, Gs, Tr, chlorophyll content and SLW couldas auxiliary selection indexes of high yield breed.Water usage efficiency (WUE) was decreased with year of release in flowering stage, but it wasincreased with year of release in maturity stage. The reason was that the increase of Tr was greater than theincrease of Pn of modern cultivars with year of release in flowering stage. WUE of old cultivars wasdecreased in maturity stage, it is the reason that Pn was reduces quicker than Tr.Intercellural CO₂ concentration (Ci) was negative correlated with year of release. Ci was low, when Pnand Gs were high. This indicated that present cultivars leaf assimilates CO₂ the ability strengthens with thesoybean cultivars change. Continually Pn increasing could be limited from stomata in leaves of presentcultivars.In seed-podding stage of crucial stage affects the soybean grow, the diurnal variation of Pn and Gswere the "double peek" curve, the peak value appears in the morning 10:00 and afternoon 15:00. Diurnalvariation of Tr was the "one peek" curve, the peak value appears in the 12:00. At the whole diurnalvariation, Pn, Gs ,Tr of four ages soybean cultivars order 1990s-2000s＞1970s-1980s＞1950s-1960s＞1920s-1940s.After last phase pod-filling, the maximal efficiency of PSâ…¡photochemistry (Fv/Fm) and actual efficiency of PSâ…¡(φ_PSâ…¡) in leaves of soybean cultivars of 1990s-2000s were higher than soybean cultivarsof 1920s-1940s, 1950s-1960s, and 1970s-1980s. The result indicated that newer soybean cultivars leaveswere slower than older soybean cultivars leaves of senescence rate. Therefore high Pn in leaves newersoybean cultivars of could provide more ATP and NADPH.The nitrate reductase activity (NRA) in the leaves of soybean was different significantly at everystage. The order of NRA from high to low was: R₂ stage＞V₄ stage＞R₄stage＞R₆ stage. There weredifference in NRA in the leaves of soybean in the same growth stage ,the CV% respectively were17.6%,8.6%,8.5% and 12.7% at V₄ stage, R₂ stage, R₄stage and R₆ stage, there were very significantdifference or significant difference.The nitrate reductase activity at different growth stage was increased linearly from 1923 to 2005,andthere was significant positive relationship between NRA and the year of release, the order of relationshiplevel from high to low is : V₄ stage＞R₂ stage＞R₆ stage＞R₄ stage.Increasing of Nitrate Reductase Activity (NRA) in the leaves and yield is close in the geneticimprovement in soybean cultivars. Therefore, NRA in the leaves could be one of selection index forhigh-yield soybean cultivars.