Cycling of Nutrients in Ecosystems, Biology tutorial


Elements that is vital to the survival of organism's cycle in ecosystems among organisms and reservoirs which are either liquid or gas (that is, oxygen, water, carbon and nitrogen) or solid (that is, phosphorus). It starts when they are incorporated from the atmosphere or from weathered rock to the bodies of organisms. The elements are unchangeable in natural conditions on earth therefore they remain in circulation when molecules pass from one Trophic level to the other. They can be recycled over and over again as they run on a closed system.

Nutrient Cycles:

All of the substances which take place in organisms cycle via ecosystems in a cyclic path comprising both biological and chemical processes known as biogeochemical cycle. Usually, the bulk of these substances are not contained in the bodies of organisms however instead exist in the atmosphere, water or in rocks. Carbon (that is, in form of carbon-dioxide), nitrogen and oxygen mainly enter bodies of organisms from the atmosphere whereas phosphorus potassium, sulphur, magnesium, sodium, calcium, iron and cobalt all of which are needed for the growth of plant come from rocks.

The cycling of materials in ecosystems starts when they are incorporated from the atmosphere or from weathered rock to the bodies of organisms. At times, they pass from these organisms to the bodies of other organisms which feed on them and at last via decomposition, they are returned to the non-living world.

After this takes place, the nutrients might start the cycle again by being incorporated into the bodies of other organisms. This procedure goes on over and over again.

There are numerous nutrient cycles; however the well known and significant cycles comprise the water cycle, the carbon cycle, oxygen cycle, nitrogen cycle, phosphorus cycle and the sulphur cycle.

Water Cycle:

Water cycles constantly from the atmosphere to the earth to the oceans and back to the atmosphere again.

Water is crucial to the functioning of living organisms that live or die on the basis of their capability to capture water and incorporate it into their bodies. Water evaporates from the oceans which cover 3/4 (three-fourth) of the earth's surface into the atmosphere a procedure powered by energy from the sun. Over land areas, around 90% of the water which reaches the atmosphere comes from plants through transpiration. Following condensation, the majority precipitation from the atmosphere falls clean and fresh directly to the oceans however, a few fall on land where it passes to the surface or subsurface bodies of the fresh water. Only around 2% of all the water on earth is fixed in any form - frozen, held in the soil or incorporated into the body of organisms. This cycle of evaporation or transpiration and precipitation goes on over and over again.

The Carbon Cycle:

The carbon cycle is mainly based on carbon-dioxide which makes up only around 0.03% of the atmosphere. Carbon is utilized to make carbohydrates, fats and proteins, the main sources of food energy.

These compounds are oxidized to discharge carbon-dioxide that can be captured through plants, algae and photosynthetic bacterial to make the organic compounds. The chemical reaction is powered by the light energy of the sun. This outcomes in the fixation of around 10% of the roughly 700 billion metric tons of carbon-dioxide in the atmosphere each and every year.

Nearly all heterotrophic organisms comprising non-photosynthetic bacteria, fungi, animals and some plants which have lost the capability to photosynthesize, get their carbon indirectly from the organisms which fix it. When their bodies decompose, organisms discharge carbon dioxide to the atmosphere. Once there, it can be reincorporated to the bodies of other animals.

The carbon cycle is extraordinary among nutrient cycles as it require not involve decomposers. Most of the organic compounds which are formed as an outcome of carbon-dioxide fixation in the bodies of photosynthetic organisms are eventually broken done and discharged back into the atmosphere or water. Though, certain carbon having compounds such as cellulose is more resistant to break-down.

The carbon in this cellulose might ultimately be incorporated into fossil fuels, like coal or oil. In global terms, respiration and photosynthesis are just about balanced, however the balance has been shifted recently due to the consumption of the fossil fuels by man. The combustion of oil, coal and gas has discharged large stores of carbon into the atmosphere as carbon-dioxide. This increase of carbon-dioxide in the atmosphere looks to be the changing global climate making it warmer.

The Nitrogen Cycle:

The main inorganic reservoir of Nitrogen is the atmosphere. Nitrogen gas comprises 78% of the earth's atmosphere however the whole amount of fixed nitrogen in the soil, oceans and the bodies of organisms is just 0.03% of that figure. This cycle can be broken down to a number of phases.


Whenever organisms excrete nitrogenous waste or die, their nitrogen is transformed to ammonium ions by the action of saprotrophic fungi and bacteria. This procedure is termed as Ammonification.


In warm, moist soils having a pH close to 7, ammonium ions are oxidized in a few days of their formation or their addition as fertilizer (Salisbury and Ross in the year 1985). The oxidation advantages of the bacteria carrying the reactions by discharging the energy which the bacteria can utilize for the synthesis of ATP. The procedure occurs in two phases.

At first, ammonium is oxidized to nitrite, by bacteria of the genera Nitrosomonas, Nitrosospira, Nitrosococcus and Nitrosolobus (Hamilton, in the year 1988). Subsequently, nitrite is oxidized to nitrate through bacteria of the genera Nitrobacter, Nitrospira and Nitrococus.                                                 

Uptake of Nitrogen by plants:

Most of the plants absorb the majority of their nitrogen as nitrate. Though numerous plants as well absorb ammonium like in forests on acidic soils where transformation of ammonium to nitrate is slow.

Nitrogen Fixation:

Nitrogen fixation is the drop of atmospheric nitrogen to Ammonium ion. It is of great significance to organisms. Altogether with Lightning, it is the natural manner in which organisms gain access to the huge reserves of nitrogen in the atmosphere. Nitrogen fixation can just be taken out by certain species of bacteria and Cyanobacteria (Postgate, 1988).  

A few of these species are free-living, finding in soil or in water. The others exist in symbiotic relationships having higher plants. The most famous of the nitrogen fixing bacteria are in the genus Rhizobium.

Such bacteria form symbiotic associations in the root nodules of numerous plants in the family Leguminosae that comprises some significant crops as groundnuts, peas, beans and clovers.


Particular proportion of the fixed nitrogen in the soil is gradually lost. Beneath anaerobic conditions, nitrate is often transformed to nitrogen gas and nitrous oxide both of which return to the atmosphere. This procedure in which some of the genera of anaerobic bacteria are taken out is termed as Denitrification. In its absence, all the nitrogen would ultimately become fixed, transformed into nitrate and washed into the oceans. Life would therefore be possible simply in marine and littoral habitats as all living organisms based on the outcomes of nitrogen fixation to synthesize proteins, nucleic acid and other essential nitrogen-having compounds. Denitrification and nitrogen fixation altogether comprise the method for returning nitrogen from the oceans to the land.

Phosphorus Cycle:

The phosphorus cycle dissimilar to those of carbon and nitrogen be deficient an atmospheric component. Phosphorus enters ecosystems via the weathering of rocks. Plants get their phosphorus from the soil either as dihydrogen phosphate or more gradually as hydrogen phosphate.  Once in an organism, although, phosphorus doesn't experience reduction; it remains as phosphate. In this form it is found in the number of compounds comprising nucleic acids, phosphorylated carbohydrates and fats. Herbivores get their phosphorus from plants whereas carnivores get theirs from herbivores. Decomposers return phosphorus to the soil as the phosphate ion.

In most of the soils and waters, phosphorus is in short supply and limits the plant growth. This is because they are relatively insoluble and are present simply in particular kinds of rock. Crushed phosphate-rich rocks found in certain areas are employed as fertilizer and added to the agricultural lands in form of superphosphate in the belief that it becomes fixed to and enriches the soil. The absorption of phosphate all along with ammonium, nitrate and the potassium ion is although, greatly aided through the presence of mycorrhizae (that is, fungus plants).

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