The Changes Of Root System Bleeding Sap Weight And The Correlation With Leaf Net Photosynthetic Rate In Soybean Cultivars Released Different Years

In the paper, in order to understand the changes of root system activity and correlation between root system activity with leaf photosynthesis of the soybean cultivar during different years, so root system bleeding sap weight (BSW) was used as an index of root system activity, root system BSW and leaf net photosynthetic rate (Pn) were measured at flowering (R2), pod growth (R4) and seed filling stage (R6) with 22 soybean varieties bred in Jilin province during 1923-2004. Then we compared the relationship between BSW with Pn and yield. So we expect that we can provide a new thinking and evidence of exploring the restriction factor of photosynthesis and direction of breeding of high yield.Under natural conditions in the field, we respectively measured leaf photosynthesis of soybean with LI-6400 portable photosynthesis system at 9 am to 11 am of flowering (R2), pod growth (R4) and seed filling stage (R6) of soybean, later sheared cotyledonary node of plant to collect bleeding sap and measured its weight.The results were showed:1,the relationship between soybean BSW and year of release in different yearsRoot system BSW were positive correlated with year of release, but it has difference between different years, the correlation of BSW with year of release was not reached significant level in 2009; it was showed a significant and extremely significant level at R2, R4 and R6 stage in 2010. Two year mean of BSW with year of release was showed significant positive correlation level at R4 stage. The genetic improvement of soybean cultivars had resulted in an increase of root system BSW. Maximum root system BSW was measured at R4 stage, second is at R2 stage, and the smallest bleeding sap weight was measured at R6 stage.2,the relationship between soybean Pn and year of releaseLeaf net photosynthetic rate (Pn) was also positive correlated with the year of release. It reached an extremely significant positive correlation level at R4 and positive correlation but not significant level at R2,R6 in 2009; it reached a significant positive correlation level at R2,R6 and an extremely significant positive correlation level at R4 in 2010; two year mean of Pn with year of release was showed positive correlation and showed extremely significant level at R4,R6。The genetic improvement of soybean cultivars had resulted in an increase of leaf Pn. Maximum Pn was measured at R4 stage, second is at R2 stage, and decreasing at R6 stage.3,the relationship between root system BSW and leaf Pn at R2,R4 and R6Related analysis of root system BSW and leaf Pn at R2,R4 and R6 shows that root system BSW with Pn was showed significant positive correlation level at R2 and R4 stage but it was not reached significant level at R6 stage. The soybean root system BSW at R2 and R4 stage could be as an index of functional leaf Pn. The analysis of ratio of Pn to BSW shows that the ratio was nearly same at R2 and R4 stage; higher Pn and lower BSW were measured at R6 stage, as the result the ratio of Pn to BSW was increased. It could be postulated that the decrease of Pn was likely correlated with the restriction of root system at R6.4,the relationship between soybean root system BSW and yield of cultivarThe result of analyzing the relationship between BSW and yield showed that it reached a positive correlation level at three phases but not significant level in 2009. The BSW with yield was showed extremely significant positive correlation level at R2 and R4 and significant positive correlation at R6. The analysis of two year mean of BSW with yield showed that the root system BSW with yield was showed that extremely significant positive correlation level at R4 and significant positive correlation level at R2 and just positive correlation level at R6, not reached the significant level.5 the relationship between soybean leaf Pn and yield of cultivarThe result of analyzing the relationship between Pn and yield showed that it reached a positive correlation level at R2 but didn't reach the significant level and it reached extremely significant positive correlation level at R4 and R6 in 2009. The Pn with yield was showed extremely significant positive correlation level at R4 and positive but not significant correlation at R2 and R6. The analysis of two year mean of Pn with yield showed that the leaf Pn with yield was showed that extremely significant positive correlation level at R4 and R6, and positive correlation level at R2.The result of this paper showed:The genetic improvement of soybean cultivars had resulted in increasing of leaf Pn, at the same time, the increasing of root system bleeding sap weight (BSW) also followed as the year of release. So the root system BSW could be used as an index of Pn of functional leaf at R2 and R4. However, the root system BSW had decreased significantly at R6, it is likely that it was reason of decreasing of net photosynthetic rate (Pn) at seed filling stage.