| Soybean is the most important food crop in China. The most significant characteristic of soybean unlike other non-legumes is that of the nodules'nitrogen fixation system during the root growth. Symbiotic nitrogen fixation of soybean nodule symbiosis is a biochemical progress that need consume large amounts of energy, and carbohydrates in carbon metabolism to provide energy and carbon source for nodule symbiotic nitrogen fixation in soybean. Lower net photosynthesis rate often lead to shortage of carbohydrates effect the ability of nodule nitrogen fixation. Acetochlor and Fomesafen are two widely used herbicides in soybean production to control grass and broad-leaf weeds, their action target are inhibition of cell division and pigment synthesis. To determine the effect of this two commonly used herbicides on carbon metabolism and nitrogenase activity in soybean for understanding mechanism that acetochlor and fomesafen effect on nodule nitrogen fixation in soybean through changes of carbon metabolism and nodule nitrogenase activity. The experiment was conducted in the year of 2009 at Xiang fang experiment farm of Northeast Agricultural University, and study changes of nodule nitrogenase activity after acetochlor and fomesafen application in soybean, meanwhile, physiology and biochemical characteristics of carbon metabolism were determined, the results as bellow:1. At 61 day after acetochlor application nodule numbers were significantly inhibited in soybean and at 75 day after treatment. Although nodule number was not significantly affected at Acetochlor 1500 ga.i./hm2 use rate the inhibited ratio of nodule number was still significant at 55.74% and 47.85% respectively at Acetochlor 3000 ga.i./hm2 and 6000 ga.i./hm2 use rate. There was no significantly inhibition on nodule number after fomesafen single application in soybean. Only 10 day after fomesafen sequential application at 525+525 ga.i./hm2 use rate was significant reduced, then the inhibition of nodule number was recovered. At 55 day after acetochlor application nodule fresh weight was inhibited significantly, and then nodule growth recovered to normal level. There was no significant affect on nodule fresh weight after fomesafen application in soybean.2. At 75 day after acetochlor application soybean nodule nitrogenase activity was inhibited significantly, the inhibition ratio of nitrogenase activity was 61.46%, 65.77% and 67.49% respectively at Acetochlor 1500 ga.i./hm2, 3000 ga.i./hm2 and 6000 ga.i./hm2 use rate. The inhibition ratio of nitrogenase activity peacked at 38 day after fomesafen single application, nitrogenase activity was reduced 0.2361mmol C2H4·g-1·h-1 and 0.2535mmol C2H4·g-1·h-1 respectively compared with control. When fomesafen sequential application at 5 to 6 trifoliolate leaf was fully expended greater biomass enhanced tolerance to fomesafen and that was the reason of nodule nitrogenase activity decreased less than fomesafen single application.3. At 61 day after Acetochlor application net photosynthesis rate was inhibited significantly in soybean, there was still obvious difference compared with control at 75 day after Acetochlor treatment. At 263 ga.i./hm2 and 525 ga.i./hm2 use rate after fomesafen single application the inhibition ratio of net photosynthesis rate was 3.72%~18.164% and 8.13%~23.41% respectively. 23 day after fomesafen application at 263+263 ga.i./hm2 use rate no effect on net photosynthesis rate was found.4. At 67 day after Acetochlor application leaf and stem soluble sugar content were inhibited significantly in soybean. At 75 day after Acetochlor application no effect on leaf and stem soluble sugar content was found at Acetochlor 1500 ga.i./hm2 and 3000 ga.i./hm2 use rate. while there was still significantly inhibited 11.70% and 15.89% respectively by Acetochlor at 6000 ga.i./hm2 use rate. At 61 day after acetochlor application root and nodule soluble sugar content was no obvious difference compared with control. At 38 day after fomesafen sequential application at 525+525 ga.i./hm2 use rate a significant inhibition was apeared. the inhibition ratio of leaf, stem, root and nodule soluble sugar content was 11.56%, 16.21%, 30.83% and 21.82% respectively.5. At 47 day after Acetochlor application in soybean starch content was significantly inhibited, and at 67 day after acetochlor application at 1500 ga.i./hm2 and 3000 ga.i./hm2 use rate no effect on leaf and stem starch content was found. The inhibition ratio of leaf, stem, root and nodule starch content was 14.25%, 13.48%, 16.06% and 20.44% respectively. Acetochlor at 6000 ga.i./hm2 use rate soybean starch content was significantly reduced after super-overwhelmed acetochlor was applied. At 31 days after fomesafen application in soybean the starch content was significantly inhibited, then the inhibition decreased and recovered by the end.6. At 47 day after acetochlor application root sucrose synthase activity(SSA) inhibited significantly in soybean. The inhibition of SSA relieve at 1500 ga.i./hm2 and 3000 ga.i./hm2 use rate. SSA was still significantly inhibited at 6000ga.i./hm2 use rate. The inhibition ratio of SSA was peacked at 55 day after acetochlor application and SSA was reduced 0.0602μmol·g-1FW·h-1, 0.1156μmol·g-1FW·h-1 and 0.1140μmol·g-1FW·h-1 respectively compared with control. At 9 day after fomesafen application SSA in root was also inhibited significantly and then the inhibition recovered. At 38 day after fomesafen application SSA in leaf was decreased significantly at 525 ga.i./hm2 use rate after fomesafen single application and at 525+525 ga.i./hm2 use rate after fomesafen sequential application.7. Soybean leaf and seed nitrogen content was no obvious difference compared with control after Acetochlor application at 1500 ga.i./hm2 use rate, and at Acetochlor 6000 ga.i./hm2 use rate the significantly inhibition ratio was 18.59% and 12.56% compared with control on soybean leaf and seed nitrogen content. At 18 day after fomesafen single application leaf nitrogen content was significantly inhibited. Only at 525+525 ga.i./hm2 use rate after fomesafen sequential application significant inhibition on soybean leaf and seed nitrogen content was found. Overwhelm use of Acetochlor and Fomesafen will destroy soybean nitrogen metabolism.8. Soybean yield was no obviously difference compared with control after Acetochlor application at 1500 ga.i./hm2 and 3000 ga.i./hm2 use rate. But at Acetochlor 6000 ga.i./hm2 use rate soybean yield was significantly inhibited 21.96% compared with control. At 263 ga.i./hm2, 525 ga.i./hm2 and 263+263 ga.i./hm2 use rate no significant inhibition on soybean yield was found after Fomesafen application. At Fomesafen 525+525 ga.i./hm2 use rate soybean yield was significantly inhibited 16.74% compared with control. Acetochlor and fomesafen over application in soybean can cause soybean yield seriously decreased and the reason comes from the significantly inhibited on carbon metabolism and lead to low efficiency of nodule nitrogenase. |
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