Nutrient Cycles

Nutrient Cycles

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Nutrient cycles are essential for the environment because it recycles important elements such as carbon, oxygen, and phosphorus. A nutrient is when organic and inorganic materials are moved and exchanged back into the production of living matter. The main types of nutrient cycles include water, carbon, nitrogen, oxygen, and phosphorus cycles. Primary producers such as plants take up inorganic nutrients from the non-living environment and convert it into organic matter that can be ingested by primary consumers. These nutrient cycles work together in balance to replenish the ecosystem with nutrients and get rid of waste.

The water cycle, also known as the hydrological cycle, is an essential process that determines the weather and climate. Water is needed by producers, such as plants, to grow, making it critical for all living things. The water cycle moves via evaporation, transpiration, condensation, precipitation, melting, and freezing. Stomata found on plant leaves and stems allow substances like water and oxygen to flow through. The infiltration process happens when water flows into soil and rock.

Oxygen is recycled between living organisms and the air and plays an important. respiration remove oxygen from the environment, while photosynthesis adds oxygen.

The carbon cycle involves a series of processes by which carbon compounds are interchanged in the environment. Carbon moves via combustion, photosynthesis, cellular respiration, precipitation, and decomposition. The burning of fossil fuels releases carbon back into the atmosphere as carbon dioxide, while carbon dioxide is taken up by plants and converted into organic molecules such as glucose. Organic molecules like glucose are broken down during cellular respiration to release energy, water, and carbon dioxide. Carbon can also be released back into the atmosphere as carbon dioxide when an organism dies and enters the decay process.


The carbon cycle
The carbon cycle

The nitrogen cycle

Nitrogen is the most abundant gas in the atmosphere. It is used in the production of amino acids, proteins and nucleic acids (DNA and RNA). Although abundant, nitrogen is tricky, in that the gaseous form present in the air is not available to all organisms. Hence, it has to be converted to more readily available forms. Only a few single-celled organisms, such as bacteria, are able to take up nitrogen in its gaseous form.

Plants can take up nitrogen in other forms such as nitrates and ammonia. These substances are produced during nitrogen fixation which describes the conversion of atmospheric nitrogen into ammonium ions, carried out by nitrogen-fixing bacteria. You can learn more about this process in our Nitrogen Cycle article.

The nitrogen cycle
The nitrogen cycle

The phosphorus cycle

Phosphorus is an important component of  ATP,  phospholipids, nucleic acids and other substances. Unlike the other nutrients we have talked about earlier in this article, phosphorous lacks the gaseous phase in the atmosphere. Phosphorus  reservoirs mainly lay in mineral form - as a phosphate ions () in sedimentary rock deposits.

The main steps in the phosphorus cycle include:

Weathering - rocks erode, due to rain and other weather events. Phosphorus is washed into the soil. Absorption by plants and animals - microorganisms are able to take up phosphorous from the soil. Plants can also absorb phosphorous directly from the soil and when they are consumed, animals also gain the nutrient. Animals can also gain phosphorous from drinking water. Decomposition - decay results in the release of phosphorus back into the environment, and the cycle of being absorbed by plants and animals can be repeated.


Microorganisms in nutrient cycles

Microorganisms, such as fungi and bacteria, can form mutual symbiotic associations with plants.

You might have noticed that sometimes viruses are included in microorganisms. However, viruses should be referred to as microbes rather than microorganisms, because they are non-living!

Microorganisms and plant symbiosis

Mutual symbiotic relationships refer to an instance where two organisms live in close physical proximity and they both benefit from the association. The relationship between nitrogen-fixing bacteria and plants is one example.

In mutualistic relationships between plants and microorganisms, microorganisms receive organic compounds, such as sugars and amino acids, from the plants. This helps them perform metabolic processes, such as photosynthesis and protein synthesis. In return, microorganisms increase the total surface area of the plant for water and mineral absorption.

Mutualism between plant roots and fungi is a mycorrhizae association.

If plants lost their associations, they would become more susceptible to droughts and fewer nutrients would be available for the plants to take up. Less susectibility to draughts comes from the fungal ability to temporarily absorb water and store it for the future that plant can utilize when needed.

Legumes and Rhizobium - Rhizobium colonize the legume plant's root cells, where they fix nitrogen. In return, they receive sugars. Endophytic fungi and plants - endophytic fungi colonize plant tissue without damaging it and release toxins to repel herbivores. They can also increase resistance to infections from other microorganisms. Azotobacter - Aztobacter are a group of free-living nitrogen-fixing bacteria. They do not directly form a relationship with the plant. However, aztobacter will increase the soil fertility by fixing nitrogen.

Human impact on the nutrient cycles

What impact do we have on nutrient cycles? We will cover a few examples below.


When crops are harvested, nutrients are removed from the soil. Human population growth and increased agriculture have caused significant changes to the nutrient cycles.

Agriculture can also accelerate land erosion, leading to more nutrients draining off. Nutrient runoff will enter rivers and oceans and will lead to eutrophication, which describes increased algae growth due to nutrient excess. Uncontrolled algae growth can form dead zones, ie, a lack of oxygen for other organisms.

The addition of fertilisers will increase levels of macronutrients and cause imbalances. This can cause a decrease in biodiversity and can have other impacts.


Similar to agriculture, felling trees removes stored nutrients vital for plant growth. Trees are major carbon dioxide consumers. Less carbon dioxide will be taken up from the environment and will lead to an increase in carbon dioxide concentration in the atmosphere. The build-up of  carbon dioxide could lead to global warming, as it is the main greenhouse gas.

You have most definitely heard about global warming mentioned before. This is for a good reason! Most of what you may have heard is about raising awareness on this issue b ecause we are the main cause of it. By burning fossil fuels, there has been an increase in greenhosue gasses, ie gasses that trap heat in our atmosphere. This includes carbon dioxide and others such as nitrous oxide. The heat trapped in the atmosphere raises our Earth's temperature which affects not only us but species diversity. In the areas where the temperatures has risen more than a species can tolerate, consequences such as suitable habitat loss and even death follow. A good example is bleaching in the coral reefs due to temperature rises.

Burning of fossil fuels

This affects the amount of nitrogen in the atmosphere. Fossil fuel releases nitrogen oxides due to combustion and consequently, they can combine with other elements, such as sulfur oxides. This leads to acid rain and smog. Excess nutrients will also wash into nearby water bodies such as rivers, causing eutrophication.

Nutrient Cycles - Key takeaways The nutrient cycle is the movement and exchange of organic and inorganic material back into the production of living matter. Energy and matter are transferred between living organisms and the non-living environment. The main nutrient cycles include the water cycle, oxygen cycle, carbon cycle, nitrogen cycle and phosphorus cycle. Plants and fungi form symbiotic associations, known as  mycorrhizae . Fungi will absorb water and minerals,  allowing plants to resist drought better and absorb nutrients more readily. Meanwhile,  fungi receive organic compounds such as sugars and amino acids from the plants. Human activity, such as the combustion of fossil fuels, deforestation and agriculture, alter nutrient cycles.

Nutrient Cycles

What is meant by a nutrient cycle?

A nutrient cycle can be defined as the movement and exchange of organic and inorganic material back into the production of living matter.

How does the nutrient cycle work?

Energy and matter are transferred between living organisms and a non-living environment. There is a movement and exchange of organic and inorganic material back into the production of living matter.

How does deforestation affect the nutrient cycle?

Removing trees from a forest subtracts stored nutrients vital for plant growth. In addition, fewer trees mean less carbon dioxide is removed from the atmosphere. This contributes to global warming as carbon dioxide is the main greenhouse gas.

What is nutrient cycling and why is it important?

Nutrients are recycled within the system. There is limited availability of usable ions in the environment. Therefore, elements such as carbon, oxygen, and phosphorus need to be recycled.

What are the main nutrient cycles in an ecosystem?

The main nutrient cycles include the water cycle, oxygen cycle, carbon cycle, nitrogen cycle, and phosphorus cycle.

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