Difference Between Carbon Cycle and Phosphorus Cycle

The key difference between carbon cycle and phosphorus cycle is that the carbon cycle is the biogeochemical cycle that describes the movement of carbon through the lithosphere, hydrosphere, biosphere, and atmosphere. Meanwhile, the phosphorus cycle describes the movement of phosphorus through the lithosphere, hydrosphere, and biosphere.

Carbon, nitrogen and phosphorus are three major elements that are important for all living beings. Circulation of these elements via biotic and abiotic components present in the ecosystems or environment is described by their biogeochemical cycles.  Carbon cycle explains the circulation of carbon elements through air, soil and water while the phosphorus cycle explains the behaviour of phosphorus through soil and living organisms. One of the important difference between carbon cycle and phosphorus cycle is that carbon mainly move thought the atmosphere while phosphorus does not interact with the atmosphere.

CONTENTS

1. Overview and Key Difference
2. What is Carbon Cycle 
3. What is Phosphorus Cycle
4. Similarities Between Carbon Cycle and Phosphorus Cycle
5. Side by Side Comparison – Carbon Cycle vs Phosphorus Cycle in Tabular Form
6. Summary

What is Carbon Cycle?

Carbon is the most abundant element on Earth. It is the main component of biological compounds as well as minerals. Carbon cycle describes the movement of carbon thought the planet. Carbon mainly cycles thought the atmosphere in the gaseous form. Carbon exists in the atmosphere as carbon dioxide gas (CO₂). CO₂is released to the atmosphere by many processes such as respiration, burning of fossil fuels, industrial emissions, microbial respiration and decomposition, etc.

Methane is another form of carbon in the atmosphere. Plants utilize atmospheric carbon dioxide for their food production by photosynthesis. In other words, plants fix carbon dioxide into carbohydrates and balance the atmospheric carbon. Moreover, carbon dioxide dissolves directly in water. Carbon dioxide also dissolves in precipitation.

Carbon exists as organic carbon in living organisms, including plants and animals. The soil is rich also in carbon. When plants and animals die, organic carbon returns to the soil. Microorganisms decompose organic materials and release carbon which can again be absorbed by the plants. Some organic carbon converts into fossil when they remain buried in the soil for many years. Combustion of organic carbons and fossil fuels, again release carbon dioxide into the atmosphere.

What is Phosphorus Cycle?

Phosphorus is a vital nutrient for plants. Since it is frequently deficient in the soil for crop production and is required by crops in relatively large amounts, it is classified as a major plant nutrient. Phosphorus can be found in water, soil and sediments cycling through them. Phosphorus is most commonly found in rock formations and ocean sediments.

The general P transformation processes in soil are weathering and precipitation, mineralization and immobilization, and adsorption and desorption. Weathering, mineralization and desorption increase plant accessible form of phosphorus. Immobilization, precipitation and adsorption decrease plant accessible form of phosphorus.

Soil contains minerals that are rich in phosphorus. With time, these minerals are subjected to the weathering process and release plant accessible forms of phosphorus to the soil. However, once these plant accessible form of phosphorus is released to the soil, they become unavailable rapidly due to the fixation or precipitation process occurring in the soil. In acidic soil, inorganic P reacts with iron and aluminum and make insoluble compounds, while in basic soil, inorganic P reacts with calcium and magnesium and form insoluble complexes.

Mineralization is the microbial conversion of organic Phosphorus to H₂PO₄^– or HPO₄^2-, forms of plant-available orthophosphates. Mineralization rate is controlled by the physical and chemical factors of the overall microbial activity.  Immobilization occurs when these plant accessible forms of phosphorus are consumed by microbes, turning P into organic P forms. The microbial P will become available over time as they die.

Organic matter mineralizes and releases phosphorus to the soil solution. Plants uptake these P from the soil solution during their growing periods. This minimizes the need for fertilizer applications and the risk of runoff and leaching of phosphorus to the water bodies that can create environmental problems.

Adsorption is another process that reduces the available form of phosphorus in the soil. During adsorption, plant-available phosphorus binds with soil particles and become fixed. The opposite process of adsorption; desorption releases adsorbed P back to the soil solution.

The cycling of phosphorus through rocks and sediments is faster than the cycling of phosphorus through plants and animals. Organic P returns to the soil when plants and animals die and decompose. After that, these organic P transform into P in sediments and rocks when they retain in the soil or ocean for millions of years. The cycle starts and continues again when the phosphorus is released from the sediments and rocks thought the weathering process.

What are the Similarities Between Carbon Cycle and Phosphorus Cycle?

• Both carbon and phosphorus are major important elements on earth.
• Carbon and phosphorus cycles describe the movements of carbon and phosphorus through soil, water and air.
• Microorganisms are involved in both cycles.
• Both cycles are important in recycling nutrients.

What is the Difference Between Carbon Cycle and Phosphorus Cycle?

The carbon cycle describes the movement of the element carbon through the ecosystems, while phosphorus cycle describes the movement of phosphorus thought the environment. So, this is the key difference between carbon cycle and phosphorus cycle. Furthermore, unlike the phosphorus cycle, the carbon cycle interacts with the atmosphere. Thus, it is another main difference between carbon cycle and phosphorus cycle.

Moreover, carbon cycle takes place fast while phosphorus cycle occurs slowly. Hence, we can consider this too as a difference between carbon cycle and phosphorus cycle.

Summary – Carbon Cycle vs Phosphorus Cycle

Carbon cycle explains the circulation of carbon through the air, water and soil. Meanwhile, the phosphorus cycle explains the movement of phosphorus through soil and living organisms. Furthermore, the carbon cycle occurs rapidly than phosphorus cycle, which occurs slowly. Moreover, carbon cycle interacts with the atmosphere while the phosphorus cycle does not interact with the atmosphere. So, this is the summary of the difference between carbon cycle and phosphorus cycle.

Reference:

1. “The Carbon Cycle.” Khan Academy, Available here.
2. “Phosphorus Cycle.” Biology Dictionary, 5 June 2017, Available here.

Image Courtesy:

1. “Carbon cycle” By Diagram adapted from U.S. DOE, Biological and Environmental Research Information System. –  (Public Domain) via Commons Wikimedia
2. “Phosphorus Cycle copy” By Welcome1To1The1Jungle at English Wikipedia (CC BY 3.0) via Commons Wikimedia