CYCLING OF NUTRIENTS IN THE ECOSYSTEM OCTOBER 13, 2011 CAPE BIOLOGY UNIT II MRS. HAUGHTON

BIOGEOCHEMICAL CYCLES Major feature of ecosystems along with energy flow. Nutrients are constantly being converted into more complex forms or broken down into simpler ones which can be reused. Usually there is a large abiotic reservoir pool of an element / nutrient. Cycling between abiotic and biotic usually slow. Human activity speeds up cycles pollution sometimes occurs.

Objective 3.5 Describe how nitrogen is cycled within an ecosystem. Include the role of microorganisms.

IMPORTANCE OF NITROGEN Humans need nitrogen to make proteins. Proteins are essential in the making: Hair fingernails Hormones Enzymes Cell membranes Blood clotting proteins And many other substances found in and on the human body

NITROGEN CYCLE

NITROGEN CYCLE Nitrogen gas is very inert (triple bond) Takes a lot of energy to spilt the bond It is needed by plants and animals for growth and repair so it must be ‘fixed’ or converted into useful forms e.g. nitrates Nitrogen-fixing bacteria and lightning (ionizing event), and industrial processes fix nitrogen

NITROGEN-FIXATION Energy consuming process Nitrogen-fixing bacteria contain the enzyme nitrogenase 5-10% nitrogen fixed by indistrial or ionizing processes Nitrogen-fixing bacteria live in the root nodules of leguminous plants (peas, beans, clover etc.) and for mutialistic relationships.

NITROGEN-FIXATION The plant gains fixed nitrogen in the form of ammonia and nitrates The bacteria gain energy and certain nutrients such as carbohydrates Legumes contribute 100 times more nitrogen than nitrogen-fixers and are sometimes added to animal feed Important nitrogen-fixing bacteria are from the genus Rhizobia, Frankia, Azotobacteriaceae

NITRIFICATION AND DECAY Animals then feed on the plants to gain nitrogen to build new cells and muscles. Other animals then feed on them. When organisms die, saprophytic bacteria and fungi decompose the proteins to amino acids then ammonia. Animal waste and excreta are decomposed like this as well Important nitrifying bacteria are Nitrosomonas and Nitrobacter.

DENITRIFICATION This is the reverse of nitrification and it reduces soil fertility. Nitrifying bacteria are inhibited by the presence of oxygen or another nitrogen source. The bacteria are facultative aerobes which means that they can survive with or without oxygen.

NITROGEN CYCLE See cycle page 311 Biological Sciences by Taylor, Green and Stout 3rd Edition.

NITROGEN CYCLE

SUMMARY OF NITROGEN CYCLE The abiotic source of nitrogen is atmospheric nitrogen gas. Nitrogen fixing bacteria convert atmospheric nitrogen to nitrates in the soil via ammonia and nitrites. Nitrates can be absorbed from the soil by plants, which convert the nitrates and incorporate the nitrogen into organic nitrogen compounds.

SUMMARY OF NITROGEN CYCLE The organic nitrogen compounds are passed on to other trophic levels through feeding. Death and decay of plants and animals returns the nitrogen to the soil as organic nitrogen compounds. Nitrifying bacteria will produce nitrates from these organic nitrogen compounds. Denitrifying bacteria are able to return nitrogen to its abiotic source by converting nitrates to nitrogen gas.

HYDROLOGICAL CYCLE Water is essential for life. The hydrological cycle helps regulate Earth’s surface temperature and distribution. It controls weather systems on a large scale because of the exchange of energy as water freezes, evaporates and ice melts. Major stores of water are oceans, seas and ice caps. Water vapour is an important green house gas.

HYDROLOGICAL CYCLE

CARBON CYCLE Main carbon store is 75 million billion tonnes in the Earth’s rocks. 5000 billion tonnes in fossil fuel reserves 150 billion tonnes in ocean upper sediment Atmospheric carbon dioxide is main source for living organisms (plants photosynthesis) Effect of human activities increases the rate of the release of carbon dioxide from fossil fuels adding to the green-house effect and global warming.

WHAT IS THE CARBON CYCLE? The carbon cycle is the sequence in which carbon is constantly being used and reused in various forms in nature. Below is a diagram of the carbon cycle. On the diagram, you will notice that not only is carbon dioxide being removed from the atmosphere, but it is being returned from the atmosphere.

REMOVAL OF CARBON DIOXIDE FROM THE ATMOSPHERE Carbon dioxide is removed from the atmosphere by the process of PHOTOSYNTHESIS. Plants use the sun’s energy, CARBON DIOXIDE and water to make glucose, starch and other carbohydrates. Animals then eat the plants as part of their NUTRITION and therefore get carbohydrates into their bodies. Sometimes when the plants and animals die, they become hard deep under the Earth’s crust (FOSSILIZATION) and become fossils that later become fossil fuels like oil and coal.

ADDITION OF CARBON DIOXIDE TO THE ATMOSPHERE Carbon dioxide can be returned to the atmosphere in three ways. They are DECOMPOSITION, RESPIRATION AND COMBUSTION. When decomposers feed on dead organisms, they use this food in the process of respiration in order to get energy to keep on living and undergoing life processes. Carbon dioxide, which is a by-product of respiration, is therefore released into the atmosphere. When animals and plants respire to make energy for their cells, they also release carbon dioxide into the atmosphere as a by-product. Lastly, when fossil fuels such as oil and coal are burned (COMBUSTION) in fireplaces, cars and other modes of transportation, carbon dioxide is released as part of the smoke.

CARBON CYCLE

SUMMARY OF CARBON CYCLE Carbon dioxide in the atmosphere and dissolved carbon dioxide in the oceans provide the major source of abiotic carbon for organisms. The carbon is fixed from the carbon dioxide by photosynthesis to form organic compounds such as carbohydrates, proteins and lipids in producers.

SUMMARY OF CARBON CYCLE The fixed carbon dioxide is then taken up by primary consumers and passed on to secondary consumers and beyond. Carbon can be returned to its abiotic source via respiration, combustion of fossil fuels, and death and decay by decomposers.

PHOSPHORUS CYCLE

Objective 3.6 Distinguish between energy flow and nutrient cycling within an ecosystem.

ENERGY FLOW AND NUTRIENT CYCLING The movement of energy from the sun to plants and then on to animals. Energy is gained during eating and used by the organism. Whatever is left, is what is passed on to the organism feeding next. Most of the energy is lost or used up before being passed on and the energy is never returned to the source. So energy flows in one direction only.

ENERGY FLOW AND NUTRIENT CYCLING On the other hand, as organisms die or release excreta, remains are left. Decomposers break these organic remains down to the simplest inorganic substances. This is important to return the nutrients like carbon, nitrogen and phosphorus back to the environment or the depletion would be disastrous as upcoming organisms would be deprived. So, nutrients are constantly being used up, broken down and reused (recycled).

Objective 3.7 Explain how energy flow and nutrient cycling are important for ecosystems to remain self-sustaining units.

IMPORTANCE OF ENERGY FLOW AND NUTRIENT CYCLING Self-sustaining means the ability function long-term without external interference. Ecosystems need plants to trap sunlight’s energy and from there herbivores then carnivores are able to survive. Ecosystem needs decomposers and various life processes such as respiration and photosynthesis to also maintain life.

IMPORTANCE OF ENERGY FLOW AND NUTRIENT CYCLING Without decomposers, simple inorganic substances would be depleted and these substances would no longer be available to making new organisms. Without respiration, carbon dioxide for plants would not be made and without photosynthesis, carbon dioxide would build up and oxygen would not be made for animals.