The nitrogen cycle refers to the movement of nitrogen within and between the atmosphere, biosphere, hydrosphere and geosphere. The nitrogen cycle matters because nitrogen is an essential nutrient for sustaining life on Earth. Nitrogen is a core component of amino acids, which are the building blocks of proteins, and of nucleic acids, which are the building blocks of genetic material (RNA and DNA). When other resources such as light and water are abundant, ecosystem productivity and biomass is often limited by the amount of available nitrogen. This is the primary reason why nitrogen is an essential part of fertilizers used to enhance soil quality for agricultural activities.
What is the nitrogen cycle?
Nitrogen cycles through both the abiotic and biotic parts of the Earth system. The largest reservoir of nitrogen is found in the atmosphere, mostly as nitrogen gas (N2). Nitrogen gas makes up 78% of the air we breathe. Most nitrogen enters ecosystems via certain kinds of bacteria in soil and plant roots that convert nitrogen gas into ammonia (NH3). This process is called nitrogen fixation. A very small amount of nitrogen is fixed via lightning interacting with the air. Once nitrogen is fixed, other types of bacteria convert ammonia to nitrate (NO3‑) and nitrite (NO2–), which can then be used by other bacteria and plants. Consumers (herbivores and predators) get nitrogen compounds from the plants and animals they eat. Nitrogen returns to the soil when organisms release waste or die and are decomposed by bacteria and fungi. Nitrogen is released back to the atmosphere by bacteria get their energy by breaking down nitrate and nitrite into nitrogen gas (also called denitrification).
A simplified diagram showing terrestrial nitrogen cycling. Credit: Wikimedia
Nitrogen levels can vary significantly in aquatic and terrestrial habitats, and can be affected by various human activities and environmental phenomena, including:
- The production and use of fertilizers for agricultural activities that increase the amount of nutrients in soil or water, especially nitrogen (and phosphorus). These nutrients increase plant and algae growth. However, increased nutrient is not always a good thing. For example, in aquatic environments nutrient-rich runoff (erosion) can cause large numbers of algae to grow. When these algae die they are consumed by bacteria which can reduce oxygen levels in the water, killing fish and other species. This process is known as eutrophication.
- The abundance (biomass) and biodiversity of bacteria, plants, fungi species that can fix nitrogen. Certain species of agricultural crops, including legumes (plants in the bean family) such as soy, clover, and peas, also host symbiotic nitrogen-fixing bacteria in their roots. As humans increase nitrogen soil levels, this can also reduce populations of plant species that are adapted to low-nitrogen soils.
- The burning of fossil fuels releases nitrous oxide (N2O), a greenhouse gas, into the atmosphere. The burning of fossil fuels also releases nitrogen oxides (NOx), sulfur dioxide (SO2), and carbon dioxide (CO2) that react with water vapor, oxygen, and other chemicals to form acid rain. Acid rain can affect freshwater sources, where increased nutrients can result in harmful algal blooms that reduce water oxygen levels and harm fish populations and other wildlife. Additionally, acid rain increases chemical weathering of rocks, including manmade structures.
- Increased precipitation can increase erosion and thus increase the transport of nitrogen (and other chemical nutrients) into soils, freshwater environments, and coastal waters.
- Deforestation, habitat loss, and erosion can reduce the nutrient levels in soils. The process of producing fertilizers also introducespollutants into the environment which alters habitats.
- Changes in ocean circulation patterns can alter the concentration and distribution of nutrients that are transported offshore. Dissolved chemical nutrients, especially nitrogen (and phosphorus) are critical for marine organisms, including the growth of plankton and algae which form the base of most ocean food webs. When organisms die they sink to the bottom of the ocean where their nutrients are released as they decay. These nutrients can be returned to the surface by ascending currents through a process known as upwelling, which is caused by offshore winds. Regions with coastal upwelling have highly productive ecosystems because of the nutrient rich upwelled water.
- Changes in atmospheric circulation patterns can alter the concentration and distribution of dust (airborne particles) that contain nitrogen (and other nutrients) for life on land and in aquatic environments.
Earth system model about the nitrogen cycle
The Earth system model below includes some of the processes and phenomena related to the nitrogen cycle. These processes operate at various rates and on different spatial and temporal scales. For example, fixation of nitrogen by bacteria happens on small spatial scales, but human use of fertilizers can impact entire ecosystems. Can you think of additional cause and effect relationships between the parts of the nitrogen cycle and other processes in the Earth system?
Explore the Earth System
Click the linked bolded terms (e.g. agricultural activities, productivity and biomass, and nutrient level) on this page to learn more about these process and phenomena. Alternatively, explore the Understanding Global Change Infographic and find new topics that are of interest and/or locally relevant to you.
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FAQs
Thus, nitrogen undergoes many different transformations in the ecosystem, changing from one form to another as organisms use it for growth and, in some cases, energy. The major transformations of nitrogen are nitrogen fixation, nitrification, denitrification, anammox, and ammonification (Figure 1).
How does nitrogen effect climate change? ›
Nitrogen fertilizers are incredibly efficient, but they make climate change a lot worse. Nitrous oxide (N2O) (more commonly known as laughing gas) is a powerful contributor to global warming. It is 265 times more effective at trapping heat in the atmosphere than carbon dioxide and depletes our ozone layer.
What impact does nitrogen have on society? ›
Excess nitrogen in the atmosphere can produce pollutants such as ammonia and ozone, which can impair our ability to breathe, limit visibility and alter plant growth. When excess nitrogen comes back to earth from the atmosphere, it can harm the health of forests, soils and waterways.
Why is it important to understand the nitrogen cycle? ›
The nitrogen cycle matters because nitrogen is an essential nutrient for sustaining life on Earth. Nitrogen is a core component of amino acids, which are the building blocks of proteins, and of nucleic acids, which are the building blocks of genetic material (RNA and DNA).
Why is nitrogen so important to life on Earth? ›
Nitrogen is found in soils and plants, in the water we drink, and in the air we breathe. It is also essential to life: a key building block of DNA, which determines our genetics, is essential to plant growth, and therefore necessary for the food we grow.
Why is nitrogen so important? ›
Nitrogen is an essential nutrient for the production of amino acids, proteins, nucleic acids, etc., and stone fruit trees require an adequate annual supply for proper growth and productivity. Nitrogen is primarily absorbed through fine roots as either ammonium or nitrate.
Is nitrogen gas responsible for global warming? ›
Nitrogenous gases also play an important role in global climate change. Nitrous oxide is a particularly potent greenhouse gas as it is over 300 times more effective at trapping heat in the atmosphere than carbon dioxide.
What will happen if nitrogen increases? ›
Excess nitrogen compounds in waterways and lakes can cause toxic algal blooms, killing off aquatic species and threatening human health. One form of nitrogen gas, nitrous oxide, is also a potent greenhouse gas and can contribute to global warming.
What impact does nitrogen have on the economy? ›
Some of the serious economic consequences of nitrogen pollution include the staggering and rising costs (in the billions of dollars annually) for treating human health maladies, purifying contaminated drinking water (from aquifers and surface waters), reducing nitrogen in wastewater treatment plants and disposal, ...
Why is nitrogen an environmental problem? ›
Nitrogen makes plants grow. But too much of a good thing is a bad thing. When too much nitrogen flows to our bays, fast-growing plants out-compete and kill slower-growing beneficial plants. Decaying plants use up oxygen, which kills fish and other marine life.
It is an important element in plant nutrition; certain bacteria in the soil convert atmospheric nitrogen into a form, such as nitrate, that can be absorbed by plants, a process called nitrogen fixation. Nitrogen in the form of protein is an important constituent of animal tissue.
What would life be like without nitrogen? ›
Life can exist without oxygen, but without plentiful nitrogen to build genes – essential to viruses, bacteria and all other organisms – life on the early Earth would have been scarce. The ability to use atmospheric nitrogen to support more widespread life was thought to have appeared roughly 2 billion years ago.
Can we live without nitrogen in the atmosphere? ›
Nitrogen is an inert gas and is not toxic. But breathing pure nitrogen is deadly to humans, since it displaces oxygen in the lungs. Hence, humans are unable to live without nitrogen as there are severe complications, dynamics and various parameters are essential to be cooperative for life without nitrogen.
How do we benefit from nitrogen? ›
Nitrogen is so vital because it is a major component of chlorophyll, the compound by which plants use sunlight energy to produce sugars from water and carbon dioxide (i.e., photosynthesis). It is also a major component of amino acids, the building blocks of proteins.
What would happen if the Earth had less nitrogen? ›
If plant nitrogen becomes less available, plants grow more slowly and their leaves are less nutritious to insects, potentially reducing growth and reproduction, not only of insects but also the birds and bats that feed on them.
How does too much nitrogen affect the environment? ›
Problems with excess levels of nitrogen in the environment
Excess nitrogen can cause overstimulation of growth of aquatic plants and algae. Excessive growth of these organisms, in turn, can clog water intakes, use up dissolved oxygen as they decompose, and block light to deeper waters.
Why is nitrogen increasing in the atmosphere? ›
The other primary reason is that, unlike oxygen, nitrogen is very stable in the atmosphere and is not involved to a great extent in chemical reactions that occur there. Thus, over geological time, it has built up in the atmosphere to a much greater extent than oxygen.
Why is nitrogen important industry? ›
Food processing companies use nitrogen in the packaging of perishable foods to increase shelf life. Metal manufacturers use N2 to prevent oxidation during the formation of new metals. Industries involved in polymer production use nitrogen gas to harden materials such as plastics and rubber.
Why is nitrogen important in industry? ›
Nitrogen gas is commonly employed in the creation of electronic components used in various devices. Nitrogen gas soldering of electronic parts is an efficient process guaranteeing high-quality finishes. Steel electroplating done using gaseous nitrogen provides a robust and durable finish that is corrosion-resistant.
What happens to nitrogen in the atmosphere? ›
Biologically: Nitrogen gas (N2) diffuses into the soil from the atmosphere, and species of bacteria convert this nitrogen to ammonium ions (NH4+), which can be used by plants. Legumes (such as clover and lupins) are often grown by farmers because they have nodules on their roots that contain nitrogen-fixing bacteria.
Growing demand on the agriculture, transport, industry and energy sectors has led to a sharp growth in the levels of nitrogen pollution and related greenhouse gas emissions.
How did nitrogen increase in the atmosphere? ›
Volcanic activity also released water vapour , which condensed as the Earth cooled to form the oceans. Nitrogen was probably also released by volcanoes which gradually built up in the atmosphere because it is unreactive.
What would happen if Earth lost nitrogen? ›
Life can exist without oxygen, but without plentiful nitrogen to build genes – essential to viruses, bacteria and all other organisms – life on the early Earth would have been scarce. The ability to use atmospheric nitrogen to support more widespread life was thought to have appeared roughly 2 billion years ago.
What will happen if nitrogen decreases? ›
If plant nitrogen becomes less available, plants grow more slowly and their leaves are less nutritious to insects, potentially reducing growth and reproduction, not only of insects but also the birds and bats that feed on them.
What is the nitrogen crisis? ›
The Netherlands is struggling with high emissions of nitrogen from agriculture, transport and industry, which threaten the country's nature and biodiversity. Agriculture is the main culprit. It has been known for decades that the country's growing livestock herd is causing environmental damage.
Does nitrogen increase growth? ›
Nitrogen is an essential element for plant growth and development; however, due to environmental pollution, high nitrate concentrations accumulate in the edible parts of these leafy vegetables, particularly if excessive nitrogen fertilizer has been applied.
Why does the earth have so much nitrogen? ›
The other primary reason is that, unlike oxygen, nitrogen is very stable in the atmosphere and is not involved to a great extent in chemical reactions that occur there. Thus, over geological time, it has built up in the atmosphere to a much greater extent than oxygen.
