Ecophysiology of Nitrogen in Symbiotic Relationships of Plants and Microorganisms

Nitrogen (N) is one of the essential elements for life on Earth and is mainly distributed in an inert form in the atmosphere, so it cannot be used by plants. Therefore, the N found in the atmosphere must undergo several transformations to be fixed in the soil and then used by plants. With the presence of N in several organic molecules, the acquisition of this element by plants has an impact on the growth and development of several agricultural crops. Understanding the metabolic mechanisms related to N and the methods of uptake, transport and use of this nutrient by plants have always been a topic of interest in several types of research. N also influences the soil microbiota, because microorganisms participate in the N cycle, especially in relation to the process of biological application of N. Thus, with the discovery of N-fixing microorganisms, it was possible to explore the impact that the microbiota would have on the plant’s N metabolism. In this context, we have gathered in this chapter, information about the ecophysiology of N in plants and how some fungi and bacteria are able to influence the metabolism of this element. We also explain a little how the association between plants and endophytic bacteria occurs, since this symbiotic relationship is very important to make N available to the plants.