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Nutrient Cycle
Nutrients – elements required for the development, maintenance, and reproduction of
organisms.
Nutrients comprise the 22 or so chemical elements known to be essential for the growth
of living organisms.
Among which nitrogen, sulfur, phosphorus, and carbon—all elements needed in relatively
large quantities (the so called macronutrients). These elements are essential for life.
It is important to recycle the nutrients in the environment for life to exist.
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Broadly speaking, nutrients can occur in
gaseous form (such as N2, CO2),
mineral form (such as apatite, the main P-containing mineral),
inorganic ionic form (NH4, NO3, SO4, H2PO4),
organic form (bound into various C-based compounds in living or dead organisms or
their products).
Nutrients are mostly taken up by plants in the ionic form and by animals in organic
forms through consumption of living or dead tissues; microorganisms in general may
use nutrients in any mineral or organic form, with sometimes high degrees of
specialization at the guild or species level.
The interconversion between forms is mediated by the ecosystem.
The cyclic process in which nutrients are transferred from the physical environment
to the living organisms and back to the environment is called nutrient cycling.
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How nutrient cycling differs from energy flow?
The energy flow refers to the transfer of energy from one trophic level to another in the
food chain and food web.
It is unidirectional. Sunlight is the ultimate energy source.
Nutrient cycling is a cyclic process that encompasses the movement of nutrients from the
physical environment to living organisms and back to the environment.
Nutrients are present on the earth where they are recycled, transformed into different
forms and reutilized.
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The nitrogen cycle is a repeating cycle of processes during which nitrogen moves
through both living and non-living things: the atmosphere, soil, water, plants,
animals and bacteria.
In order to move through the different parts of the cycle, nitrogen must change forms.
In the atmosphere, nitrogen exists as a gas (N2), but in the soils it exists as nitrogen
oxide, NO, and nitrogen dioxide, NO2, and when used as a fertilizer, can be found in
other forms, such as ammonia, NH3, which can be processed even further into a
different fertilizer, ammonium nitrate, or NH4NO3.
Nitrogen Cycle
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There are five stages in the nitrogen cycle, and will now discuss each of them in turn:
1. Fixation
2. Nitrification
3. Assimilation
4. Ammonification
5. Denitrification
Atmospheric nitrogen (N2) which is primarily available in an inert form, is converted
into the usable form -ammonia (NH3).
Stages in Nitrogen Cycle
Fixation
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Types of Nitrogen Fixation
1.Atmospheric fixation: A small amount of nitrogen can be fixed when lightning provides the
energy needed for N2 to react with oxygen, producing nitrogen oxide, NO, and nitrogen
dioxide, NO2. These forms of nitrogen then enter soils through rain or snow, which are then
used by plants.
2. Industrial nitrogen fixation: It is a man-made alternative that aids in nitrogen fixation.
Under great pressure, at a temperature of 600°C, and with the use of a catalyst, atmospheric
nitrogen and hydrogen can be combined to form ammonia (NH3). Ammonia can be used
directly as fertilizer, but most of its is further processed to urea and ammonium nitrate
(NH4NO3).
This process, made commercially feasible by Carl Bosch, came to be called the Haber-Bosch
process or the synthetic ammonia process.
3.Biological nitrogen fixation: Small part of atmospheric nitrogen (Nitrogen gas) is converted
into biologically acceptable nitrogenous compound (NH3) by biological organisms such as
bacteria, BGA etc. and the process is called biological nitrogen fixation.
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Two kinds of nitrogen-fixing microorganisms are
recognized:
free-living (nonsymbiotic) fixers, including
• the cyanobacteria (or blue-green algae)
• Anabaena and Nostoc
• and genera such as Azotobacter, Beijerinckia,
and Clostridium
mutualistic (symbiotic) fixers such as
• Rhizobium, associated with leguminous plants
• and various Azospirillum species, associated
with cereal grasses.
More than 90 percent of all nitrogen fixation
is effected by them.
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Ammonia is converted into nitrates by nitrifying bacteria. This conversion is very
important as ammonia gas is toxic for plants.
Until recently this was thought always to be accomplished in two steps:
1. Bacteria of the genus Nitrosomonas oxidize NH3 to nitrites (NO2
−).
2NH3 + 3O2 → 2NO2
– + 2H+ + 2H2O
2. Bacteria of the genus Nitrobacter oxidize the nitrites to nitrates (NO3
−
2NO2
– + O2 → 2NO3
–
Nitrification
However, in 2015, two groups reported finding that bacteria in the genus Nitrospira were
able to carry out both steps: ammonia to nitrite and nitrite to nitrate. This ability is called
"comammox" (for complete ammonia oxidation).
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Nitrate Assimilation
Soil nitrates produces as a result of nitrification can be taken by plants for the synthesis of
amino acids, chlorophyll. This is known as nitrate assimilation.
From plants (producers) nitrogen as biomolecule enters the food chain and moves to
animals (consumers) and decomposers.
Ammonification
This is another process by which ammonia can be generated. Organic remains of plants and
animals are broken down in the soil by some decomposers (bacteria i.e. Pseudomonas,
Bacillus, Clostridium, Serratia), fungi i.e. Alternaria, Aspergillus, Mucor, Penicillium) and
Actinomycetes i.e. Streptomyces) can convert organic nitrogen compound into ammonia.
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Denitrification
Is the reverse of nitrification that occurs in the deep layers of soil where the bacteria convert
soil NO3- into other gaseous compounds like NO2, NO and finally into N2.
This process is carried out by the denitrifying bacterial species- Clostridium, Pseudomonas ,
Bacillus , Paracoccus.
NO3 → NO2→ NO → N2
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Anammox stands for Anaerobic Ammonium Oxidation. The process was discovered in the
early nineties and has great potential for the removal of ammonia nitrogen in wastewater.
Anammox (anaerobic ammonium oxidation), is a reaction that oxidizes ammonium to
dinitrogen gas using nitrite as the electron acceptor under anoxic conditions, was an
important discovery in the nitrogen cycle.
The reaction is mediated by a specialized group of planctomycete-like.
NH4
+ + NO2
− → N2 + 2H2O
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So far, 11 species have been detected and enriched from the biomass of sewage
treatment plants and the most populous species are C. “Brocadia anammoxidans,”
Candidatus “Kuenenia stuttgartiensis,” Candidatus “Scalindua wagneri,” and
Candidatus “Scalindua brodae.”
In addition, Candidatus “Scalindua sorokinii” was detected in the anoxic water column
of the Black Sea, providing the first direct evidence for anammox bacteria in the natural
environment.
Anammox bacteria have a cell compartment known as the anammoxosome, which is
the site of anammox catabolism.
The lipid bilayer membrane surrounding this anammoxosome contains unusual lipids,
so-called “ladderane” lipids
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Advantages
The anammox reaction may account for as much as 50% of the denitrification occurring in
the oceans.
50% less oxygen is used (results in energy and cost savings)
Anammox bacteria do not require organic carbon (e.g. methanol) as they do in nitrification
100% less organic carbon emission
Saves 90% of operational costs in sludge disposal, as compared to the conventional
nitrification/denitrification processes
Disadvantages
Not a lot of knowledge available (skilled operation and maintenance required)
High construction costs if the Anammox process replaces the conventional nitrification/
denitrification in treatment plants
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Why is the Nitrogen Cycle Important?
Nitrogen's chemical bonding properties allow it to create structures such as DNA and
RNA nucleotides.
The amino acids from which proteins are built. Without nitrogen, these molecules would
not be able to exist.
Plants need nitrogen as this element is an important component of chlorophyll.
Consequently, chlorophyll is vital for the process of photosynthesis, so lack of nitrogen
can cause deficiency disorders such as stunted growth and other abnormalities
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The carbon cycle is a series of events that involves the cyclic movement and
transformation of carbon between living organisms and the environment. Essentially, this
is a natural way of reusing carbon molecules in different geographic locations.
The carbon cycle is divided into the following steps:
Photosynthesis
Respiration
Decomposition
Fossilization
Combustion
Carbon Cycle
Carbon Cycle Steps
39. Course: Classification of Insects and Pest Management Course
Code ZOO482. Instructor: Dr. Syed Ishtiaq Anjum, Asst. Prof.
Department of Zoology, KUST -- Email: ishtiaq@kust.edu.pk
39
40. 40
What is the Water Cycle?
The water cycle, also known as the hydrologic cycle or the hydrological cycle, describes
the continuous movement of water on, above and below the surface of the Earth.
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Stages of Water Cycle
There are many processes involved in the movement of water
1. Evaporation
Evaporation occurs when the physical state of water is changed from a liquid state to a gaseous state.
A considerable amount of heat, about 600 calories of energy for each gram of water, is exchanged during the
change of state.
Evaporation can occur on raindrops, and on free water surfaces such as seas and lakes. It can even occur from
water settled on vegetation, soil, rocks and snow. There is also evaporation caused by human activities.
Heated buildings experience evaporation of water settled on its surfaces.
Evaporated moisture is lifted into the atmosphere from the ocean, land surfaces, and water bodies as water
vapor. Some vapor always exists in the atmosphere.
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2. Condensation
Condensation is the process by which water vapor changes it's physical state from a
vapor, most commonly, to a liquid.
Water vapor condenses onto small airborne particles to form dew, fog, or cloud in sky.
Condensation is brought about by cooling of the air or by increasing the amount of
vapor in the air to its saturation point.
When water vapor condenses back into a liquid state, the same large amount of heat (
600 calories of energy per gram) that was needed to make it a vapor is released to the
environment.
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3. Precipitation
Precipitation is the process that occurs when any and all forms of water particles fall
from the atmosphere and reach the ground.
Precipitated water may fall into a water body or it may fall onto land. It is then dispersed
several ways. The water can adhere to objects on or near the planet surface or it can be
carried over and through the land into stream channels, or it may penetrate into the soil,
or it may be intercepted by plants.
4
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RUNOFF
If the water from rainfall flows down the sides of mountains and hills; eventually
forming rivers. This process is called runoff.
In colder regions, icecaps form when the amount of snowfall is faster than the rate of
evaporation. The biggest icecaps on earth are found at the poles.
When the snow melts into water, it also leads to runoff.
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“Phosphorus cycle is a biogeochemical process that involves the movement
of phosphorus through the lithosphere and hydrosphere.”
Phosphorus is an important element for all living organisms. It forms a significant part
of the structural framework of DNA and RNA.
They are also an important component of ATP.
Humans contain 80% of phosphorus in teeth and bones.
Since phosphorus and phosphorus-containing compounds are present only on land,
atmosphere plays no significant role in the phosphorus cycle
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Steps of Phosphorus Cycle
Following are the important steps of phosphorus cycle:
1.Weathering
2.Absorption by Plants
3.Absorption by Animals
4.Return to the Environment through Decomposition
1. Weathering
Phosphorus is found in the rocks in abundance. That is why the phosphorus cycle starts in
the earth’s crust. The phosphate salts are broken down from the rocks. These salts are washed
away into the ground where they mix in the soil.
2. Absorption by Plants
The phosphate salts dissolved in water are absorbed by the plants. However, the amount of
phosphorus present in the soil is very less. That is why the farmers apply phosphate
fertilizers on agricultural land.
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4. Absorption by Animals
The animals absorb phosphorus from the plants or by consuming plant-eating animals.
The rate of the phosphorus cycle is faster in plants and animals when compared to rocks.
5. Return of Phosphorus Back to the Ecosystem
When the plants and animals die they are decomposed by microorganisms During this
process, the organic form of phosphorus is converted into the inorganic form, which is
recycled to soil and water.
Soil and water will end up in sediments and rocks, which will again release phosphorus
by weathering. Thus, the phosphorus cycle starts over.
The aquatic plants absorb inorganic phosphorus from lower layers of water bodies.
Since phosphate salts do not dissolve in water properly, they affect plant growth in
aquatic ecosystems.
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Human Impact on Phosphorus Cycle
A number of human activities, use of fertilizers, artificial eutrophication, etc. has a great
impact on the phosphorus cycle.
The phosphorus fertilizers increase the level of phosphorus in the soil. Overuse of these
fertilizers reduces the fertility of the soil and is also harmful to the microorganisms
present in the soil. When these are washed away into the nearby water bodies, they are
hazardous to aquatic life.
During the shipping of food from farms to cities, the amount of phosphorus that is
washed away in water causes eutrophication. This leads to the growth of algae. These
form algal blooms or die, which is toxic to the aquatic ecosystem.
