Mineral metabolism of Nitrogen-15 isotope in soil and plant

Nitrogen is an essential life element for plants. Its lack produces death to cells. A 90 per cent of organic compounds contains N wich is present in its reduced form (NH3). The soil, the atmosphere and nitrogen fertilizers are the main sources of nitrogen for plants. It is mostly absorbed in the form of NO3; in the process, energy is used and there is a relation between N-absorption and photosynthesis. During this process, water and the influence of physical-chemical factors have a paramount part in the soil-plant systems. Biologic research using isotopic techniques with 15N has enlightened certain absorption, metabolic and biological N-fixation processes. By comparison of the 15N and 14N isotopic 15N/15N in N-fixing, and N-non fixing plants, it is possible to calculate and differentiate the N contribution of the soil, the fertilizer and the atmosphere