Nutrient Cycles

Table of Contents

Nutrient Cycling Definition 

The nutrient cycle is the key to all life on earth. While there are 6 main nutrient cycles, all of them depend on  the same thing. The transfer of energy and matter from non-living chemicals to living organisms. 

All of the nutrients cycles share another key element. They all require microorganisms to properly function. 

Microorganisms are involved in all 6 of the main nutrient cycles. And, in fact, microorganisms are the major recyclers on the planet. In other words, they are the major nutrient recycling factor among living organisms. 

The 6 Major Nutrient Cycles

  • The Carbon Cycle
  • The Water Cycle
  • The Nitrogen Cycle
  • The Sulphur Cycle
  • The Phosphorus Cycle
  • The Oxygen Cycle

The Carbon Cycle

Like all the nutrient cycles we will talk about the carbon cycle involves both non-living chemicals and living organisms. 

As to a short, definitive explanation, I like this carbon cycle definition.

The carbon cycle is the process in which carbon travels from the atmosphere into organisms and the Earth and then back into the atmosphere. Plants take carbon dioxide from the air and use it to make food. Animals then eat the food and carbon is stored in their bodies or released as CO2 through respiration.

Microorganisms and the Carbon Cycle

Let’s add a bit to our definition. Where the definition talks about “animals” lets add microorganisms. 

Microorganisms play a critical role in the carbon cycle, facilitating the decomposition of organic matter and the release of carbon dioxide into the atmosphere. Through processes like respiration and fermentation, these microscopic organisms break down dead plants and animals, transforming complex organic compounds into simpler inorganic molecules. This decomposition releases carbon dioxide back into the environment, contributing to the global carbon pool.

 Additionally, certain microorganisms, such as photosynthetic bacteria, can fix carbon from the atmosphere, converting it into organic matter, thereby influencing the overall balance of the carbon cycle.

The Water Cycle part of the Nutrient Cycle

There are 4 main parts to the water cycle, also known as  the hydrologic cycle. As with all of the nutrient cycles, there are many subparts that are beyond are discussion here. 

So for our purposes, the 4 parts of the water cycle are:

  • Evaporation – occurs when water is heated by the sun. Transpiration can be thought of as a type of evaporation. 
  • Convection – Convection in the water cycle is when the air near the surface is heated, then rises
    taking heat with it. Water vapour in the air gets cold and changes back into liquid,
    forming clouds. This is called condensation
  • Precipitation – We’re all familiar with the types of precipitation; rain, sleet, snow, hail. 
  • Storage/Collection – most of the Earth’s water is stored. In fact about 96% of all water is stored in the ocean. 

Microorganisms and the Water Cycle – Nutrient Cycle

 All life needs water and microbes are no acception. 

Recently, scientists have discovered that microbes play an important role in ice formation in clouds. They are the most efficient ice forming catalysts. The formation of ice in clouds is important as this is how snow and rain begin. 

The Nitrogen Cycle - Nutrient Cycle

Most of us know a bit about the nitrogen cycle. Here’s our nitrogen cycling definition. 

The nitrogen cycle is a biogeochemical cycle whereby Nitrogen is chemically converted into multiple forms. It then circulates among marine ecosystems, terrestrial ecosystems, and the atmosphere. Nitrogen can be converted by chemical, physical and biological processes. 

So let’s break this down a bit. 

Most of the Nitrogen in the atmosphere is in the form of N2. In fact the atmosphere is made up of about 78% N2. 

The problem is most plants and animals cannot use the Nitrogen that it in the atmosphere. And Nitrogen is an essential element for living organisms. 

Nitrogen is required in amino acids (the building blocks of proteins) and in nucleic acids (RNA and DNA). 

Microorganisms and the Nitrogen Cycle

This is the part of the nitrogen cycle where microorganisms come into play. 

There is an entire group of soil microbes that can convert atmospheric N2 into a usable form NH3 (ammonia). 

This ammonia is then utilized a different group of soil bacteria, nitrifying bacteria. 

The nitrifying bacteria can convert the ammonia into either N02 (nitrates) or NO3 (nitrites). All three forms of nitrogen, ammonia, nitrates, and nitrites can be utilized by plants and microorganisms in soils. 

The final step of the nitrogen cycle is also performed by bacteria, denitrification. Denitrification is the biological conversion of  nitrates to N2. The N2 then returns to the atmosphere to complete the nitrogen  nutrient cycle. 

As you can see, this is another nutrient cycle that could not be performed without soil microorganisms. 

The Sulphur Cycle - Nutrient Cycle

The next example of nutrient recycling is the sulphur cycle. 

The sulphur cycle is also a biogeochemical cycle whereby sulphur circulates through nature in various forms. 

Sulphur is a vital nutrient for both plants and animals as it is a component of some amino acids, such as cysteine and homocysteine. As we saw before, amino acids are the building blocks of proteins. 

Microorganisms and the Sulphur Cycle – Nutrient ReCycling

Some Bacteria have the ability to reduce Sulphur to H2S. Others can oxidize Sulphur into SO4. 

The reduction of Sulphur into sulfuric acid is interesting and can cause environmental issues. This, however, is not our main focus. 

It’s the SO4 that we are most interested in as this is the form of Sulphur that can be absorbed by plant roots. 

Once absorbed by the roots, the SO4 can be incorporated into amino acids and then proteins. 

Importantly, the oxidation of elemental Sulphur requires both water and oxygen. 

The Phosphorus Cycle

Phosphorus is abundant on the Earth’s surface in the form of phosphates typically found in rocks. 

Plants need phosphorus for photosynthesis, in DNA and RNA and in energy reactions in the for of ATP and ADP. 

The inorganic phosphates can be absorbed by the plant and then transferred to animals when they ingest the plants. 

Microbes assist in the cycle by returning the phosphorus to the soil during decomposition of plants and animals. 

In this way, phosphorus cycles through the ecosystem. 

The Oxygen Cycle

The oxygen cycle is how oxygen circulates between non-living environment and living organisms like plants and animals. 

The Oxygen cycle can be broken down into three main steps. 

  •  Plants, as a byproduct of photosynthesis, release O2 into the atmosphere. 
  • Aerobic organisms, like animals and most microorganisms utilize the free O2 in respiration. 
  • Finally, the same aerobic organisms, release CO2 into the atmosphere. Plants utilize the CO2 in photosynthesis and the cycle starts again. 
In this manner, oxygen cycles through the Earth’s various ecosystems. 
Nutrient cycles and nutrient recycling is important to all life on earth. 


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