The comparison of different Robinia pseudoacacia organs regarding amount of deriving nitrogen from biological nitrogen fixation process

Black locust (Robinia pseudoacacia L.) is one of the most famous plant species in the world, regarding nitrogen fixation ability. It is widely used in reforestation projects in the world. The main question of this study was that, whether the different parts of Robinia (i.e. roots, stems and leaf) derived same proportion of their required nitrogen from biological nitrogen fixation process. The collected seeds of Robinia were planted in similar greenhouse conditions. After 2 months, the seedlings of Robinia were inoculated with a suspension of mixed Rhizobium. At six months from the start of the greenhouse trials, the seedlings received the equal amount of (NH4)2 SO4 (100 cc) contain 11.03 N15. After one week, they were harvested and separated into leaves, stems, and roots. The samples were dried, weighed, and the N15 excess was measured. The N15 excess concentration was used as an index for comparison the amount of nitrogen derived from biological nitrogen fixation for each plant organs. The results did not show any significant difference amongst leaf, stem and roots of Robinia in terms of the nitrogen derived from biological nitrogen fixation procedure. Therefore, the most accessible part of plant (i.e. leaf) can be used for calculating the nitrogen proportion of nitrogen derived from biological nitrogen fixation process.