Study on key enzyme activity in nitrogen metabolism and the content of molybdenum and iron in alfalfa under different NO3--N/NH4+-N ratio
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DOI:10.7606/j.issn.1000-7601.2017.03.30
Key Words: NO3--N/NH4+-N ratio  alfalfa  nitrogen metabolism  enzyme  molybdenum  iron
Author NameAffiliation
HAO Feng College of Grassland Science, Gansu Agricultural University/Key Laboratory of Pratacultural Ecosystem, Ministry of Education/Pratacultural Engineering Laboratory of Gansu Province/Sino-US Center for Grazingland Ecosystem Sustainability, Lanzhou Gansu 730070, China 
LIU Xiao-jing College of Grassland Science, Gansu Agricultural University/Key Laboratory of Pratacultural Ecosystem, Ministry of Education/Pratacultural Engineering Laboratory of Gansu Province/Sino-US Center for Grazingland Ecosystem Sustainability, Lanzhou Gansu 730070, China 
FAN Jun-jun College of Grassland Science, Gansu Agricultural University/Key Laboratory of Pratacultural Ecosystem, Ministry of Education/Pratacultural Engineering Laboratory of Gansu Province/Sino-US Center for Grazingland Ecosystem Sustainability, Lanzhou Gansu 730070, China 
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Abstract:
      By solution culture method, ‘Gannong No.3’ alfalfa was chosen as the experimental material to explore the effects of NO3--N/NH4+-N ratios(1/7、1/3、3/5、5/5、5/3、3/1、7/1) based on nitrogen supply of 210 mg·L-1 on the activity of nitrate reductase(NR) and nitrogenase, and the content of molybdenum(Mo) and iron(Fe) in organs of alfafa during the whole growth period. The results showed that: (1) NR activity and Mo content was consistent:leaf>root>stem, while Fe content was root>leaf>stem. With the proportion of NO3--N increasing, NR activity in each organ became higher. In the early stage, when NO3--N/NH4+-N equaled to 7/1, NR activity was the highest. The influence of different ratio on Mo content in root during seedling stage was similar to NR activity, that is to say, in large proportion of NO3--N it was the highest. During budding stage, the same as nitrogenase activity, in 1/7 it was highest. During mature stage, same as nitrogenase and NR activity, in 5/3 it was highest. The influence of different ratio on Fe content in root was similar to nitrogenase activity, that is to say, it was highest at 1/7 in seedling and 5/3 from full-bloom to mature. (2) NR and nitrogenase activity showed a single-peak curve during the whole growth period, that is to say, NR activity was the highest during full-bloom stage and nitrogenase activity was the highest during podding stage. NR activity was higher under larger proportion of NO3--N in different ratios during the whole growth period. Nitrogenase activity was the highest in 1/7 at seedling and budding, and from full-bloom to mature it was the highest in 5/3. Mo and Fe content in the stem and leaf was consistent, they were the highest for larger proportion of NH4+-N from budding to full-bloom and highest for larger proportion of NO3--N from podding to maturity. (3) Relationship between NR and nitrogenase activity differed in the whole growth period. At the early growth stage (from seeding to budding), NR activity was highest in 7/1 and lowest in 1/7. Nitrogenase activity was in the opposite situation, suggesting that there was an antagonistical relationship between NR and nitrogenase activity. From full-bloom to mature, both NR and nitrogenase activity was highest in 5/3, they accelerated each other.