| Symbiotic nitrogen fixation of soybean nodule provided the source of nitrogen,and the symbiotic nitrogen fixation of soybean nodules need energy from the inside of the nodule carbon metabolism and the main energy of carbon metabolism was from photosynthesis.About an hallf of the total nitrogen required by the plant come from nitrogen fixation.Nitrogen fixation played an important role in soybean yield formation.Fomesafen was one of the commonly used herbicides in soybean production in China now and its target was plant protoporphyrin oxidase.The phytotoxicity problem became more and more serious because of the heavy applications of fomesafen.Thus,it was important to study the inhibition mechanism of nodule's nitrogenase activity,which was great significance to improve the nitrogen fixation efficiency of soybean nodules.The effect on photosynthetic carbon metabolism in soybean as breakthrough point to reveal the physiological mechanism of inhibiting the nitrogenase activity of soybean nodules after fomesafen treatment,by researching on the relationship between the carbon metabolism inside nodule and nitrogenase activity.The main results were as follows:1.The nodule number were inhibited after fomesafen appliacted,337 g a.i./hm~2 and 675 g a.i./hm~2,the only 7th day after treatment the nodule number were significantly difference compared with CK.The nodule fresh weight and dry weight the 14 th day after treatment significantly difference compared with CK and it return to normal later.2.Nitrogenase activity of nodules decreased significantly compared with CK after different dosage fomesafen treatment and with the increase of dosage the inhibition of nitrogenase activity strengthened.Inhibition of nitrogenase activity was still existed in 28 th day.3.Chlorophyll content of soybean leaves cut down obviously after treatment and 675 g a.i./hm~2's decreased above the level of 337 g a.i./hm~2's treatment.At the 28 th day the chorophyll content became normal.4.Photosynthetic rate of soybean were significantly difference compared with CK.The highest inhibition rate of leaf photosynthetic rate appeared in the 21 th day and in the 28 th daysinhibition was released,photosynthetic rate return to normal level.The nitrogenase activity and leaf photosynthetic rate had a positive correlation,it had a significant positive correlation in the 14th?21th and 28 th separately after different dosage fomesafen treatment.5.Nodule sucrose content decreased significantly after treatment.337 g a.i./hm~2 and 675 g a.i./hm~2 's highest inhibition rate were at the 14 th and 7th day respectively and it recover at 28 th day.The nitrogenase activity and nodule sucrose content had a positive correlation,337 g a.i./hm~2 was significant positive correlation in the 7th day,675 g a.i./hm~2 was significant positive correlation in the 7?28th day.The results showed that the change of nitrogenase activity was related to the content of sucrose in nodules.6.The activity of sucrose synthase(decomposition direction)in nodules decreased significantly,SS activity was not significant difference with 337 g a.i./hm~2 in the 7th day and significant difference with 675 g a.i./hm~2.The SS activity was not signficant difference at the 28 th day with both dosage fomesafen treatment.The nitrogenase activity and SS activity had a significant positive correlation in the 7th day.7.Compared with CK,the content of ammonia in nodule bacteroid decreased significantly after treatment.The nitrogenase activity and ammonia content in nodule bacteroid had a significant positive correlation in the 7?14?28th day with 337 g a.i./hm~2 and had a significant positive correlation in the 7?28th day with 675 g a.i./hm~2.The decrease of ammonia content in the bacteria showed that the activity of nitrogenase was significantly inhibited by Fomesafen.The content of ammonia in nodule cytoplasm was significantly higher than that in control and the nitrogenase activity and ammonia content in nodule cytoplasm had a negative correlation,It indicated that the ammonia in the cytoplasm could not be used in time to form a large amount of ammonia accumulation,feedback inhibited the process of nitrogen fixation.8.337 g a.i./hm~2 and 675 g a.i./hm~2 caused reduction of yieid rate of 3.69% and 15.15% respectively?... |
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