Cycling of Materials in the Ecosystem

Role of Microorganisms in the Ecosystem

Microorganisms carry out the bulk of the processing of compounds in most nutrient cycles. They are integral to the biogeochemical cycle of nutrients in the soil by interconverting various compounds of nitrogen, carbon, and other elements. We will explain the roles of microorganisms in more detail as we discuss specific carbon, nitrogen and water cycles.

Carbon Cycle in the Ecosystem

Carbon is the building block of all forms of life on earth. It is the central element for making complex biomolecules such as sugars, Proteins and DNA. Carbon is also found in the inorganic form of carbon dioxide (CO₂) in the atmosphere. CO₂ is a greenhouse gas essential for keeping the earth warm and maintaining its temperature suitable for life. Without CO₂, the earth would be frozen solid. Too much CO₂ in the atmosphere can also be problematic, as it can raise the average temperature beyond the optimum range and cause extreme weather events.

The carbon cycle describes the natural exchange of carbon atoms in different forms between the atmosphere, living organisms and the soil. Because our beloved planet and its atmosphere form a closed system, the amount of carbon in this system is always the same. It is the location of carbon atoms that continually changes. The carbon cycle has five main stages: Photosynthesis, decomposition, Respiration, combustion, and exchange.

Photosynthesis

Photosynthesis allows producers to uptake the carbon dioxide in the air and is essential in maintaining an oxygenated environment and cycling carbon. They use water, carbon dioxide and the energy from sunlight to produce high-energy Organic Molecules.

Photosynthesis provides a source of energy for all living organisms. Photosynthetic producers, such as plants on land and phytoplankton in the ocean, reside at the bottom of the food chain in most ecosystems, which is why they are called primary producers.

Decomposition

Decay is an essential component of the nutrient cycle, responsible for recycling dead organic matter into nutrients that other living organisms, usually plants, can reuse. After an organism dies, its body starts to degrade quite rapidly. Decomposing microorganisms play a vital role at this stage, as they break down complex Biological Molecules into simpler products. This way, the carbon stored as Biomass is returned to the environment.

Saprotrophic Bacteria can be either aerobic (requiring oxygen) or anaerobic (working without oxygen). Aerobic decomposers release nutrients more efficiently than anaerobic decomposers, which release large amounts of carbon dioxide and methane as by-products.

Over millions of years, dead inorganic matter (which has not been decomposed) will form fossil fuels under the pressure and heat from the earth's crust. These fossil fuels serve as a carbon sink, storing carbon away from the atmosphere.

Respiration

Animals are unable to perform photosynthesis. So, they rely on obtaining energy from the food they ingest through cellular Respiration.

Respiration is the opposite reaction to photosynthesis. It involves releasing the energy stored in glucose by using oxygen to convert it to carbon dioxide and water. The carbon dioxide released can then be used for photosynthesis.

Combustion

Combustion is the process of burning something. Combustion and respiration are very similar to each other, and they both involve the use of oxygen to release energy and produce carbon dioxide and water. While the only substrate for respiration is glucose, all organic materials that contain carbon can undergo combustion.

By burning the wood that has been cut from a tree or petrol obtained from fossil fuels, the carbon stored in them is released into the atmosphere. Therefore, combustion plays a vital role in the carbon cycle, despite often being quite alarming!

Fossil fuels are formed very slowly over thousands of years. But humans have been burning fossil fuels much faster than the rate they are created. This has resulted in the release of carbon stored for thousands of years into the atmosphere and has significantly contributed to global warming.

Exchange

Another critical stage in the carbon cycle is exchange. Carbon dioxide and water continually circulate in the environment and interact with one another. CO₂ from the atmosphere can dissolve in the oceans and form carbonic acid. This product of carbon dioxide and water is a weak acid, essential for maintaining the oceans' pH, making it suitable for marine organisms. If too much carbon dioxide is released into the environment, more will dissolve, making the oceans more acidic. Organisms that live in the oceans are susceptible to the pH of the water, and changes can significantly impact marine Biodiversity.

Nitrogen Cycle in the Ecosystem

Nitrogen is an essential element for living organisms found in the environment in organic and inorganic forms.

The Nitrogen cycle describes the exchange of nitrogen between various organic and inorganic forms as it is passed between the atmosphere and land-based ecosystems. The interconversion of nitrogen compounds occurs through both biological and physical processes. Four main steps are involved in the nitrogen cycle: nitrogen fixation, ammonification, nitrification, and denitrification.

Nitrogen fixation

Nitrogen gas (N₂) is abundantly present in the atmosphere but is inaccessible to plants and animals while in the gaseous state. Nitrogen fixation converts nitrogen gas to inorganic nitrates and nitrites that plants can take up. This occurs through processes in the atmosphere or by living microorganisms.

Most nitrogen fixation is done by specific bacteria called diazotrophs in the soil. They contain a special enzyme called nitrogenase that catalyses the reaction between nitrogen gas and hydrogen atoms in water to form ammonia, which is subsequently converted to nitrates. Some diazotrophs symbiotically live in the root nodules of legumes. They fix nitrogen for the plant and, in exchange, receive Carbohydrates from it.

Plants use the nitrates from nitrogen fixation to form complex Biological Molecules needed to grow. Herbivores then eat them. This way, the fixed nitrogen is passed on to animals.

Ammonification

The nitrogen in animals and plants is in the organic form of complex biological molecules. When these organisms release their waste products or after they die, the nitrogen present in them is still going to be organic. Bacteria and Fungi break down these complex organic compounds into inorganic ammonium in an ammonification process.

Nitrification

Plants can uptake ammonia but are unable to store it. Too much ammonia can be toxic for plants, so ammonia needs to be converted to nitrates to be usable. This process is called nitrification.

Nitrifying bacteria contain Enzymes that catalyse the oxidation of ammonia to nitrites. Another group of bacteria then further oxidise nitrites to nitrates. Nitrates can then be taken up by plants and used to build complex Organic Molecules.

Denitrification

While nitrification describes ammonia oxidation to nitrates, denitrification reduces nitrates to nitrites and eventually to nitrogen gas. By doing the opposite of nitrogen fixation, denitrification completes the nitrogen cycle.

Specific Types of Bacteria use the nitrate in the soil and convert it to nitrogen gas. These bacteria live deep in the soil and favour anaerobic conditions, such as waterlogged grounds.

Water Cycle in the Ecosystem

Water is another material constantly being exchanged between different states and locations. The water molecule that falls with the rain today might have been flowing in a river yesterday or have been in the arctic ice cap thousands of years ago. This is due to water being able to change states at relatively small temperature differences.

Water is essential to all lifeforms on earth since it is the primary substrate of many reactions in living organisms. The water cycle ensures that fresh water is distributed globally so all living organisms can access safe, usable water.

The water cycle has four major stages: Evaporation, condensation, precipitation, and collection.

Evaporation

Evaporation describes the transition of water from a liquid state to a gas. The heat from the sun provides the energy for this transition. Water vapour is also released from the Transpiration of plants.

Condensation

As the water vapour in the air rises, it cools down and condenses back into liquid form.

Precipitation

As water droplets accumulate and merge, they get bigger and heavier. They eventually begin to fall with the rain or snow. This is called precipitation.

Collection

The water that falls with rain or snow flows on the ground and joins with the rivers. Or it seeps into the ground and enters the underground water. Eventually, rivers and groundwater flow to lakes and oceans, where water is collected. The oceans freeze in cold environments such as the earth's poles to form ice caps. They are also collections of water that can be released after melting.