基础代谢氮循环 英文

基础代谢氮循环英文
Fundamental Metabolic Nitrogen Cycle.
Nitrogen, a key element for life, undergoes a complex cycle of transformations known as the nitrogen cycle. The fundamental metabolic nitrogen cycle involves the assimilation of inorganic nitrogen into organic compounds by living organisms, followed by the release of nitrogen back into the inorganic pool through decomposition and excretion.
Assimilation.
The first step in the nitrogen cycle is the
assimilation of inorganic nitrogen into organic compounds. This process is carried out by plants, algae, and certain bacteria. Plants absorb nitrate (NO3-) and ammonium (NH4+) from the soil, while algae and bacteria fix atmospheric nitrogen (N2) into ammonia (NH3) through nitrogen fixation.
Nitrogen fixation is a crucial step in the nitrogen cycle, as it converts inert atmospheric nitrogen into a form that can be used by living organisms. The enzyme nitrogenase, found in certain bacteria such as Rhizobium, catalyzes this reaction.
Ammonification.
Once nitrogen has been assimilated into organic compounds, it can be released back into the inorganic pool through ammonification. This process involves the decomposition of organic matter by bacteria and fungi. During ammonification, organic nitrogen is converted into ammonia (NH3).
Nitrification.
Ammonia can then undergo nitrification, a process carried out by nitrifying bacteria. Nitrifying bacteria convert ammonia into nitrite (NO2-) and nitrate (NO3-). Nitrite is an intermediate product that is rapidly oxidized to nitrate by other nitrifying bacteria.
Assimilation into Plants.
Nitrate and ammonium are the primary forms of inorganic nitrogen that are assimilated by plants. Plants absorb
these ions from the soil and use them to synthesize amino acids, proteins, nucleic acids, and other nitrogen-containing compounds.
Excretion.
Animals obtain nitrogen by consuming plants or other animals. The nitrogen contained in ingested food is assimilated into organic compounds and used for various metabolic processes. Excess nitrogen is excreted as urea, uric acid, or ammonia, depending on the organism.
Denitrification.
Denitrification is the final step in the nitrogen cycle, where nitrate and nitrite are converted back into atmospheric nitrogen (N2). This process is carried out by
denitrifying bacteria, which use nitrate or nitrite as an electron acceptor in anaerobic respiration.
Denitrification plays a critical role in balancing the nitrogen cycle by removing excess nitrogen from the ecosystem and returning it to the atmosphere.
Importance of the Nitrogen Cycle.
The fundamental metabolic nitrogen cycle is essential for sustaining life on Earth. It provides a continuous supply of nitrogen to living organisms and ensures the availability of nitrogen for plant growth and the production of food and other resources.
Disruptions to the nitrogen cycle, such as excessive fertilizer application or pollution, can have significant consequences for ecosystems and human health. Understanding the nitrogen cycle is therefore important for managing nitrogen resources and mitigating environmental impacts.
Additional Processes.
In addition to the fundamental metabolic nitrogen cycle, there are other processes that contribute to the cycling of nitrogen, including:
Assimilatory Nitrate Reduction: Plants can also reduce nitrate to ammonia through assimilatory nitrate reduction. This process occurs in the cytoplasm of plant cells and provides ammonia for amino acid synthesis.
Nitrite Reduction: Nitrite can be reduced to ammonia
by nitrite reductase enzymes found in certain bacteria and plants. This process is important for removing nitrite from the environment and preventing its accumulation.
Anammox: Anammox bacteria can convert ammonium and nitrite directly into dinitrogen gas (N2O). This process is particularly important in marine environments and
contributes to the removal of nitrogen from the ecosystem.
These additional processes further illustrate the complexity and interconnectedness of the nitrogen cycle,
which is essential for maintaining the health and productivity of ecosystems worldwide.。