Circulation in Ecosystems

1. Circulation in Ecosystems Decomposition Nutrient Cycling

2. Materials in ecosystems need to be recycled and reused. Decomposition and decay play a role in this.

3. Decomposition • Decomposition is the process whereby organisms obtain their energy through breaking down dead organic matter, this releases inorganic nutrients. These are then available for uptake by plants and other primary producers.

4. 2 main types of decomposer – - detritivores and decomposers Detritivores • These are detritis eating invertebrates that break detritis down into humus. Detritis – organic debris e.g. leaf litter Humus – organic portion of soil that makes it fertile and productive

5. Decomposers These are usually bacteria and fungi, they breakdown dead and decaying material into inorganic nutrients, carbon dioxide and water. e.g. nitrogen in protein is brokendown to ammonium or nitrate ions.

6. Decomposition is dependant upon and limited by • Type of detritis. Deciduous tree material is faster at decaying than coniferous material. • Type and abundance of decomposer • Conditions e.g. temperature, moisture level, oxygen availability

7. Nutrient Cycling The continual production and growth of new organisms requires a constant supply of raw materials. Resources on the planet are not infinite. The processes of death, decomposition and decay are equally as important as the processes of assimilation, production and growth

8. Nitrogen and phosphorous are essential elements in the construction of all organisms on earth.

9. Nitrogen Cycle • Nitrogen is found in 3 main forms in the ecosystem: - nitrogen gas in the atmosphere - inorganic nitrogen compounds in the soil e.g. nitrate - organic compounds in organisms (protein) The nitrogen cycle involves the transfer of nitrogen between these 3 forms.

11. Nitrogen cycle basic steps: • Plants take up ammonium and nitrate minerals • Cyanobacteria and leguminous plants e.g. clover, are able to take up atmospheric nitrogen and convert it into organic nitrogen (nitrogen fixation). The enzyme responsible for this conversion is nitrogenase. In cyanobacteria nitrogenase is contained in structures called heterocysts, in leguminous plants it is found in root nodules.

12. Anabaena (cyanobacteria) root nodules heterocyst

13. Ammonia in the soil is converted into nitrite by bacteria e.g. nitrosomonas and nitrococcus. Nitrobacter then converts nitrite into nitrate. These 2 processes are referred to as nitrification. • Nitrate is taken up by plants/primary producers and can be assimilated into amino acids or nucleic acids. These assimilated nitrogen products then pass along the food chain from one trophic level to another.

14. Bacteria are also responsible for decomposing dead organisms and animal waste into ammonia, called ammonification. This makes the ammonia available for bacteria carrying out the nitrification reactions. • A process of denitrification can also occur by anaerobic denitrifying bacteria. This is an example of a loss of nitrogen from the cycle.

15. Water Saturation and Oxygen Levels • Decomposition and nitrification require oxygen. Therefore in water saturated areas little nitrogen is transferred into the nitrate and ammonia forms, making nitrogen slow down or stop. Under anaerobic conditions denitrification is favoured .

16. In aquatic systems the level of productivity is limited by the nutrient level of that system. Low phosphate levels, for example, will limit the rate of primary productivity. Phosphates are used by organisms to construct nucleic acids, ATP and membranes.

17. Phosphates have often been added to an aquatic system e.g. through fertilizer run off or sewage, and it has as a result increased the primary productivity levels of the aquatic system (increase in plant growth and decay). This produces large populations of algae: algal blooms, which can lead to deoxygenation and consequently a loss of diversity.