Grain legumes are important agricultural plants due to their use in human diets, livestock farming and due to symbiotic nitrogen fixation. Grain legumes are a staple food and are a good source of protein, starch, fiber, vitamins and minerals. Legume production produces small amount of greenhouse emissions, has low water consumption and promotes sustainable agriculture. With symbiotic nitrogen fixation legumes improve the nitrogen balance in the soil and because of that reduce the consumption of mineral fertilizers. During growth, they reduce erosion and retain soil heat and moisture. Symbiotic nitrogen fixation takes place in the root nodules of host plants that belongs to legume family (Fabaceae). In the root nodules nitrogen fixing bacteria from the subclasses alpha and beta proteobacteria are found. Symbiosis is a specific process, as each strain of the bacteria has a certain range of hosts, which can be narrow or wide. In addition, it includes many unrelated genera of bacteria and presents different phenotypic characteristics and development strategies between different pairs of symbionts. In symbiotic relationship, bacteria receive water and nutrients in exchange for nitrogen fixation. Most of the fixed nitrogen is used by the host plant and some of it is stored in root nodules. Nodulation and bacteria activity are influenced by environmental factors like soil temperature and moisture, salinity, soil pH, minerals, metals and pesticides in the soil and drought. A balanced diet of host plants is important, especially a sufficient amount of phosphorus and molybdenum in the soil.
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