Plants absorb nitrogen through a process called nitrogen fixation.

Nitrogen fixation
Nitrogen is an essential nutrient for plants as it is a building block of proteins, enzymes, and chlorophyll. However, the majority of nitrogen in the atmosphere is in the form of nitrogen gas (N2), which is relatively inert and cannot be directly utilized by plants. Therefore, plants must obtain nitrogen from the soil in a form that they can use.

Nitrogen-fixing bacteria
Some plants have a symbiotic relationship with nitrogen-fixing bacteria, such as Rhizobium and Frankia. These bacteria live in the root nodules of certain plants, such as legumes and some non-leguminous plants. The bacteria convert atmospheric nitrogen gas into a usable form, such as ammonium (NH4+), through a process called nitrogen fixation.

Rhizobium-legume symbiosis
In the case of legumes, such as soybeans, peas, and clover, a specific type of nitrogen-fixing bacteria called Rhizobium forms nodules on the roots of the plant. The Rhizobium bacteria invade the root hairs of the plant and multiply within the plant cells, forming nodules. Inside these nodules, the bacteria convert atmospheric nitrogen gas into ammonium through the enzyme nitrogenase. The plant provides energy and nutrients to the bacteria, while the bacteria provide usable nitrogen to the plant.

Non-leguminous nitrogen-fixing plants
In addition to legumes, some non-leguminous plants also have nitrogen-fixing bacteria associated with their roots. For example, certain trees, such as alders and Casuarina, form symbiotic relationships with the nitrogen-fixing bacteria Frankia. These bacteria also convert atmospheric nitrogen gas into usable forms for the plant.

Uptake of nitrogen by plants
Once the nitrogen is fixed by the bacteria, it is released into the soil as ammonium ions (NH4+). The plant's roots absorb these ions through specialized transport proteins. The absorbed ammonium ions are then assimilated into organic compounds, such as amino acids, in the plant's cells. These organic compounds are used to build proteins, enzymes, and other essential molecules required for the plant's growth and development.

Conclusion
Plants obtain nitrogen through a process called nitrogen fixation, which involves a symbiotic relationship with nitrogen-fixing bacteria. These bacteria convert atmospheric nitrogen gas into a usable form, such as ammonium, which is then absorbed by the plant's roots. This nitrogen is essential for the plant's growth and plays a crucial role in various metabolic processes.

By the help of some nitrogen fixed bacteria,i e:-- Rhizobium,Nitro Bactor,Nitraso Monas...
The plant get the nitrogen from the soil..