Nutrient Cycle

1.0Definition of Nutrient Cycle

All the types of material required by the ecosystem in addition to energy, are available continuously to the system through recycling. Thus there is a constant exchange of materials between the living organism and their abiotic environment through the recycling of materials. This is called the nutrient cycle.

2.0Nutrient Cycle in Ecosystem 

• Nutrient cycle in ecosystems involves the dynamic movement and transfer of essential elements among living organisms, soil, water, and the atmosphere. Plants play a pivotal role by absorbing nutrients from the soil through their roots. Decomposition of organic matter by microorganisms releases nutrients back into the soil, forming a crucial part of the nutrient cycle. These nutrients are then taken up by plants, initiating a transfer through the food chain as herbivores consume plants and carnivores consume other organisms.
• Excretion by animals and decomposition of dead matter contribute to nutrient recycling, completing the cycle. Nutrient leaching and runoff from rainwater can wash away nutrients, impacting soil fertility and contributing to environmental issues. Nitrogen-fixing bacteria convert atmospheric nitrogen into plant-usable forms, and human activities, such as agriculture and industry, can disrupt natural nutrient cycles. Efforts to understand and manage nutrient passage are essential for maintaining ecological balance, sustaining biodiversity, and addressing challenges posed by human activities on nutrient cycles in ecosystems.

3.0Examples of Nutrient Cycle

Nutrient recycling encompasses both biotic and abiotic elements, some important nutrient cycle are as follows : 

1. Carbon cycle : 

• Main reservoirs of carbon are atmosphere, Ocean, Carbonate, Rocks, Coal and Petroleum. The carbon released from them is present in the atmosphere in the form of carbon dioxide. Carbon is present in every organic component of an organism. The green autotrophs utilize CO2 from the air to synthesize food materials which are obtained by other organisms as food. Carnivores obtain their carbonic food from the herbivores. These carbonic matter produce CO2 through the oxidation or respiration which dissolve in air or water and again utilized by the plants.

• Carbon constitutes 49% of the dry weight of organisms and is next only to water. Atmosphere only contains about 1% of total global carbon.
• If we look at the total quantity of global carbon, we find that 71 percent carbon is found dissolved in oceans. This oceanic reservoir regulates the amount of carbon dioxide in the atmosphere.
• Carbon cycling occurs through the atmosphere, ocean and through living and dead organisms.
• According to one estimate 4 × 1013 kg of carbon is fixed in the biosphere through photosynthesis annually.

2. Phosphorus cycle :

• Main source of phosphorus is rocks. It comes from the weathering of phosphorus containing rock in the soil. Plants absorb this phosphorus from the soil and transfer this phosphate to animals and after the death of animals it is released again into the lithosphere by the action of decomposers (Phosphate-solubilising bacteria). Phosphorus is the main constituent of protoplasm, plasma membrane, bones and teeth.
• Sometimes some of the elements like phosphorus and calcium reach into the sea through water, from where they transform into rocks. They separate from the cycle for a long time so it is also known as sedimentary cycle. But when these rocks break after sometime then this phosphorus is again made available to the sea plant or sea weeds, which pass into fish and sea birds. The excretory materials of birds on the rocks of sea shore is called Guano and it is a source of phosphorus.
• Note : Plants absorb phosphate from the soil in the form of orthophosphate (PO43–)
• Difference between Carbon and Phosphorus cycle :

(i)   Atmospheric inputs of phosphorus through rainfall are much smaller than carbon.

(ii) Gaseous exchanges of phosphorus between organism and environment are negligible.

3. Nitrogen cycle : 

• The nitrogen cycle is a fundamental process in nature, involving the continuous movement and transformation of nitrogen through various stages. Nitrogen gas in the atmosphere is converted into ammonia by nitrogen-fixing bacteria in the soil. Plants take up ammonia and other nitrogen compounds, incorporating them into proteins. Animals consume these plants, passing the nitrogen along the food chain. Decomposition of organic matter releases nitrogen back into the soil, where it can be used again by plants. Denitrifying bacteria convert nitrates back into nitrogen gas, completing the cycle.

4. Oxygen cycle : 

• The oxygen cycle is a vital biogeochemical process that involves the continuous movement of oxygen through Earth's atmosphere, biosphere, and lithosphere. Oxygen is produced primarily through photosynthesis by plants, algae, and cyanobacteria, wherein they convert carbon dioxide into oxygen. This released oxygen is then utilized by animals and other organisms during respiration, forming a dynamic cycle. Additionally, oceans play a crucial role by absorbing and releasing oxygen through various physical and biological processes.

5. Water cycle : 

• The water cycle is a continuous and essential natural process that describes the movement of water through the Earth's atmosphere, land, and oceans. It begins with the evaporation of water from oceans, lakes, and rivers into the atmosphere. This water vapor then condenses to form clouds, and precipitation occurs when these clouds release water in the form of rain, snow, or sleet. The water returns to the Earth's surface, where it can either evaporate again, be absorbed by plants, or flow into rivers and oceans, completing the cycle.

4.0Importance Of Nutrient Cycle

• The nutrient cycle is vital for the health and sustainability of ecosystems. It ensures the continuous flow and recycling of essential elements like carbon, nitrogen, and phosphorus, supporting the growth and development of living organisms. Nutrient cycles contribute to maintaining soil fertility, regulating climate through processes like carbon sequestration, and preserving water quality by managing nutrient levels.
• This cyclical flow of nutrients sustains biodiversity, enhances agricultural productivity, and mitigates environmental pollution. Recognizing the importance of nutrient cycles is essential for adopting sustainable practices that preserve the balance of ecosystems and contribute to the overall well-being of the planet.