How is nitrogen transferred from the atmosphere to plants?
Nitrogen is primarily transferred from the atmosphere to plants through a process called nitrogen fixation, carried out mainly by bacteria and to a small extent by lightning.
The atmosphere contains nitrogen gas (N₂), which plants cannot use directly. For plants to access nitrogen, it must be converted into reactive forms like ammonia (NH₃). This conversion is achieved through natural processes.
Biological Nitrogen Fixation
- The Main Pathway: The most significant way nitrogen from the atmosphere becomes available in ecosystems is through biological nitrogen fixation.
- The Agents: This process is carried out by certain types of bacteria. These bacteria can live freely in the soil or reside in a mutually beneficial relationship within the roots of specific plants (like legumes).
- The Conversion: These bacteria possess enzymes that allow them to convert nitrogen gas (N₂) directly from the atmosphere into ammonia (NH₃). This conversion makes atmospheric nitrogen accessible to the biological world.
- The Process Name: This essential biological conversion of atmospheric nitrogen into ammonia is known as nitrogen fixation. Most nitrogen enters ecosystems via these bacteria.
Atmospheric Nitrogen Fixation
- A Less Common Method: While much less prevalent than biological fixation, a small amount of atmospheric nitrogen is fixed through non-biological means.
- The Cause: This occurs when lightning interacts with the air. The intense energy from a lightning strike can break the bonds of nitrogen and oxygen molecules in the air, allowing them to combine and form nitrogen oxides. These compounds are then carried down to the Earth's surface by rain.
- Contribution: A very small amount of nitrogen is fixed into usable forms through this lightning-induced process.
These two processes are the primary ways atmospheric nitrogen is converted into forms that can enter the soil and eventually be taken up and utilized by plants for growth and development.
| Method | Agent/Cause | Relative Amount of Nitrogen Transferred | Process Description (as per reference) |
|---|---|---|---|
| Biological Nitrogen Fixation | Certain kinds of bacteria | Most nitrogen entering ecosystems | Convert nitrogen gas into ammonia (NH3) |
| Atmospheric Nitrogen Fixation | Lightning interacting with the air | A very small amount | Nitrogen is fixed via lightning interacting with air |
