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The Mystery of Nitrogen: Why is atmospheric nitrogen so difficult for plants to use?
Nitrogen is one of the most important elements on Earth, accounting for 78% of the atmospheric composition. However, why is such abundant nitrogen difficult to be directly utilized by plants? This is mainly because nitrogen in the atmosphere exists in the form of nitrogen gas (N2), which cannot be absorbed by plants. To understand this, we must delve into the process of the nitrogen cycle, which involves a series of biogeochemical processes such as nitrogen transformation, fixation, and assimilation.
Basic process of nitrogen cycle
The nitrogen cycle is a complex process involving steps such as nitrogen fixation, assimilation, ammonification, nitrification and denitrification. These processes help convert atmospheric nitrogen into a form that plants can use and ensure the healthy functioning of ecosystems.
Nitrogen fixation
The process of nitrogen fixation is to convert nitrogen gas (N2) into nitrate and nitrite that can be used by plants. This process is mostly carried out by free-living or symbiotic bacteria, such as rhizobia, which form a symbiotic relationship in the roots of leguminous plants.
Maybe you don’t know that about 30% of fixed nitrogen is produced through the Haber-Bosch process, which is an important method of industrial nitrogen fixation.
How plants use nitrogen
Plants absorb nitrate and ammonium ions in the soil and convert them into organic compounds such as amino acids. Especially in the symbiotic relationship with rhizobia, leguminous plants obtain more abundant nitrogen sources, thereby increasing the nitrogen content of nitrogen-poor soil.
Ammonification and nitrification
Ammonification is the process of converting organic nitrogen into ammonia radicals, which occurs when organisms die or when waste is broken down. The ammonia is then oxidized into nitrite and nitrate, a process called nitrification, which is dominated by bacteria in the soil.
The high toxicity of ammonia (NH3) requires it to be converted into the safer nitrate form to protect plant growth.
The role of denitrification
Denitrification is the process of reducing nitrate back to nitrogen (N2), mainly under anoxic conditions. This process completes the nitrogen cycle and helps release nitrogen back into the atmosphere.
Human influence on the nitrogen cycle
With the increase in human activities, the nitrogen cycle has been greatly changed. Factors such as human agriculture, industrial emissions and traffic pollution have led to a surge in bioavailable nitrogen. This not only changes the balance of natural ecosystems, but also poses a threat to human health.
In fact, the current eutrophication of water bodies caused by excess nitrogen has become one of the global environmental problems.
Impact on natural systems
Large-scale nitrogen fertilization has led to a series of ecological problems, including reduced biodiversity and impaired plant health. Therefore, while we enjoy the fertile soil brought by nitrogen, we must also consider how to better manage and utilize this resource to maintain ecological balance.
Conclusion
Most forms of nitrogen in the atmosphere cannot be directly utilized by plants. This process is complex and affected by many factors. With the increase in human activities, the nitrogen cycle has been completely changed, which has triggered a series of environmental problems. Can we find effective ways to solve these problems and make nitrogen use more rational and sustainable?
