The Study on Dynamics of Nitrogen Fixation Efficiency of Alfalfa-Rhizobia Symbiosis
This study investigated the temporal dynamics of nitrogen fixation efficiency in the symbiosis between alfalfa(Medicago sativa cv.Gannong No.9)and Sinorhizobium meliloti LL11.The objective was to identify the stage of optimal nitrogen fixation for improving nitrogen conversion and utilization in alfalfa.Over a 42-day period following rhizobia inoculation,the experiment evaluated changes in nodule morphology and structure,fixation capacity,plant phenotype,soluble substance content,and activities of key enzyme of nitrogen metabolism in alfalfa.The entropy-weighted technique for order preference by simi-larity to ideal solution(TOPSIS)method was employed to determine the stage of most efficient nitrogen fixation.The results showed that:(1)Effective nodule number,diameter,and weight all progressively increased until 42 days post-inoculation(dpi).The number of rhizobia-infected cells within nodules peaked at 35 dpi(992),followed by a decline.(2)Nitrogenase activity[0.9619 μmol/(g·h)],leghemoglobins content(2.6081 mg/g),and nitrogen fixation potential per plant(0.0283 μmol/h)all reached their highest levels at 35 dpi and were significantly higher compared to other time points(P<0.05).(3)Shoot height,root length,and dry weight of shoot and root in M.sativa cv.Gannong No.9 also exhibited significant increases,culminating at 42 dpi.(4)Soluble sugar content in roots peaked at 21 dpi,while soluble protein content reached its maximum at 42 dpi.Activities of nitrate reductase(NR),nitrite reductase(NiR),glu-tamine synthetase(GS),and glutamate synthetase(GOGAT)in both leaves and roots were significantly higher at 35 dpi compared to other stages(P<0.05).The entropy-weighted TOPSIS analysis identified 35 dpi as the stage of high-efficiency nitrogen fixation,followed by a decline thereafter.
Medicago sativaSinorhizobium melilotiRoot nodulesNitrogen fixation dynamicsKey enzymes of nitrogen metabolism
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