NO_3^--N/NH_4^+-N不同配比下紫花苜蓿氮代谢关键酶及钼、铁元素含量研究

Study on key enzyme activity in nitrogen metabolism and the content of molybdenum and iron in alfalfa under different NO_3^--N/NH_4^+-N ratio

以西北地区广泛种植的优质植物性蛋白饲料紫花苜蓿"甘农3号"为试验材料,在室外防雨网室内,采用盆栽营养液沙培法,在适宜氮素供应水平210 mg·L-1基础上,研究NO_3^--N和NH_4^+-N混合的7种配比(NO_3^--N/NH_4^+-N分别为12.5/87.5、25/75、37.5/62.5、50/50、62.5/37.5、75/25、87.5/12.5,依次标为1/7、1/3、3/5、5/5、5/3、3/1、7/1)对紫花苜蓿全生育期各部位硝酸还原酶(NR)、固氮酶活性及钼(Mo)、铁(Fe)营养吸收的影响。结果表明:(1)从部位来看,紫花苜蓿NR活性、Mo含量趋势一致,均表现为:叶>根>茎,而Fe含量则表现为根>叶>茎;不同配比下各部位NR活性均表现为配比中NO_3^--N比例大时,其活性较高,尤其是生长前期当NO_3^--N/NH_4^+-N为7/1时,各部位NR活性均最高;不同配比对根中Mo含量的影响在苗期与NR趋势相近,在NO_3^--N比例大时达最高。现蕾期与固氮酶活性相同,1/7时最高。成熟期同固氮酶与NR活性,均为5/3时最高;不同配比对根中Fe含量的影响与固氮酶活性变化趋势相一致,苗期均为1/7处理最高,盛花期至成熟期均为5/3处理最高。(2)从生育期来看,紫花苜蓿全生育期NR和固氮酶活性变化趋势均呈单峰曲线;NR活性在盛花期最高,即盛花期氮代谢能力最强,且各生育期均为配比中NO_3^--N比例大时NR活性高,氮代谢能力较强;固氮酶活性在结荚期最高,即结荚期根瘤固氮能力最强,且苗期和现蕾期均表现为1/7处理其活性最高,盛花期至成熟期5/3处理活性最高;不同配比对茎和叶中Mo、Fe含量的影响基本相同,现蕾期至盛花期在配比中NH_4^+-N比例大时含量最高,结荚期至成熟期在配比中NO_3^--N比例大时含量最高。(3)NR和固氮酶活性相互关系在整个生育期表现不同:在紫花苜蓿生长前期(苗期至现蕾期),NO_3^--N/NH_4^+-N=7/1时NR活性最大,1/7处理NR活性最小,而固氮酶活性则相反,二者表现出拮抗关系;在紫花苜蓿生长中、后期(盛花期至成熟期)NR活性与固氮酶活性均在NO_3^--N/NH_4^+-N=5/3时达最大值,二者又相互促进。

By solution culture method, ‘ Gannong No？ 3 ’ alfalfa was chosen as the experimental material to explore the effects of N〇 3 - 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 high-est. 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. Nitroge-nase 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 an- tagonistical relationship between NR and nitrogenase activity. From full-bloom to mature, both NR and nitrogenase activi-ty was highest in 5/3, they accelerated each other.