Study On Physiological Characteristics Of Leaf Senescence Of Soybean Cultivars With Different Released Years In Jilin Province

In order to find out the changes of physiological characteristics of cultivated soybean cultivars grown in different periods in Jilin Province,the soybean cultivars cultivated from 1923 to 2006 were divided into four periods,the first period was before 1960,the second period was from1961to1980,the third period was from1981 to 2000 and the fourth period was after 2001.The leaf gas exchange parameters,specific leaf weight,leaf area per plant,and physiological characteristics were measured in R2(flowering stage),R4(podding stage),R6(seed filling stage)and R7(maturation stage)in 2015 and 2016,To research the physiological characteristics of soybean leaf senescence,delay the senescence of leaves,especially to prevent premature aging,so that it can continue to transport photosynthetic products to the grain yield to provide a theoretical basis for yieldincreasing and seed breeding.The results were as follows: 1.Changes of senescence gas exchange parameters in soybean leaves during the leaf senescence at different growth stagesWith the advance of plant growth period,the plant began to aging gradually from the flowering period to the grain stage,the net photosynthetic rate was expressed as the first period<the second period<the third period<the fourth period.Therefore,rate ofnet photosynthetic ratedeclined is the first period>the second period>the third period>the fourth period.The transpiration rate of leaves of soybean cultivars at different growth stages increased first and then decreased with the growth period.The transpiration rate was the highestduringthepodding stage,and then began to decline gradually,finally to the minimum at maturity.The stomatal conductance of the leaves of the cultivated soybean varieties at different growth stages showed the trend of increasing first and then decreasing with the growth period.Thestomatal conductance is the largest during podding period,and then begins to decrease gradually to the minimum maturity.Both rate of stomatal conductance declined expressing the first period> second period> third period> the fourth period.2.Changes of chlorophyll in soybean leaves at different growth stagesThe chlorophyll content of soybean cultivars at different growth stages increased firstly after declined with the growth period.The chlorophyll content was the highest during podding stage,and then began to decrease gradually,achieved value of minimum at maturation stage.And the rate ofchlorophyll content decreased in soybean varieties was the first period> the second period> the third period> the fourth period.3.Change of leaves areasoybean cultivars at different growth stagesLeaf area of soybean cultivars at different times showed a trend of increasing firstly and then decreasing with the growth period.The leaf area of soybean cultivars was the largest at podding stagefor the first,second and third period,but the leaf area of the soybean cultivars was the largest at the maturation stage,and then began to decrease gradually for the fourth period.And the photosynthetic effective leaf area of soybean varieties showed the first period<the second period<the third period<the fourth period.4.Changes of specific leaf weight in soybean leaves at different growth stagesThe specific leaf weight of the cultivated soybean varieties at different stages showed a trend of increasing first and then decreasing with the growth period.Specific leaf weight wasthe largest during seed filling period,then began to gradually decline to the minimum at flowering period.At the same time,the ratio of specific leaf weight decreased was in the first period> the second period> the third period> the fourth period.5.Changes of soluble sugar and soluble proteins in soybean leaves at different growth stagesThe soluble sugar content of the soybean leaves of the first and second stage was increased with the growth period,and the soluble sugar content increased to the maximum at the mature stage,and at seed filling stage reached the minimum.The activity of soluble sugar in leaves of soybean cultivars increased gradually with the advance of period,and the soluble sugar content increased to the maximum at maturity.The content of soluble protein in the leaves of the first and second stage was increased first and then decreased with the growth period,and the soluble protein content reached the maximum at the podding stage.At the maturation period reached the minimum.The activity of soluble protein in the leaves of the third and fourth stage was increased with the growth period,the soluble protein content increased tomaximum atseed filling stageand declined to minimum at the maturation stage.6.Changes of protective enzyme activity and malondialdehyde content of soybean cultivars in different growth periodsThe activity of CAT and SOD in the leaves of soybean cultivars at different stages showed a trend of increasing and then decreasing with the growth period,and the activity of SOD and CAT in R7 was the lowest.The activities of protective enzymes in leaves of soybean cultivars at different times were expressed as the first period< the second period< the third period<the fourth period.The activity of POD,CAT and MDA in the leaves of soybean cultivars increased gradually with the advance of period,and the POD activity,CAT and MDA increased to the maximum at the mature stage.The POD activity of soybean cultivars breedingat different stages was the first period<the second period< the third period< the fourth period,MDA was expressed as the first period> the second period> the third period> the fourth period.