1 / 22

Nitrogen Cycle

Nitrogen Cycle. Nitrogen Cycle Model that describes the movement of nitrogen in its many forms between the  hydrosphere ,  lithosphere ,  atmosphere  and biosphere . What is Nitrogen.

angeni
Télécharger la présentation

Nitrogen Cycle

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Nitrogen Cycle Nitrogen Cycle Model that describes the movement of nitrogen in its many forms between the hydrosphere, lithosphere, atmosphere and biosphere.

  2. What is Nitrogen • The chemical element of atomic number 7, a colorless, odorless unreactive gas that forms about 78 percent of the earth's atmosphere. Liquid nitrogen (made by distilling liquid air) boils at 77.4 kelvins (-195.8°C) and is used as a coolant.

  3. RNA=ribonucleic acid, a nucleic acid present in all living cells. Its principal role is to act as a messenger carrying instructions from DNA for controlling the synthesis of proteins. Nitrogen • Nitrogen (N) is an essential component of DNA, RNA, and proteins, the building blocks of life. • All organisms require nitrogen to live and grow. • The majority (78%) of the Earth’s atmosphere is N2.

  4. Nitrogen’s triple bond • Although the majority of the air we breathe is N2, most of the nitrogen in the atmosphere is unavailable for use by organisms. • This is because the strong triple bond between the N atoms in N2molecules makes it relatively inert (like a noble gas).

  5. How can we use N2? WE CAN’T! • In order for plants and animals to be able to use nitrogen, N2 gas must first be converted to more a chemically available form such as ammonium (NH4+) or nitrate (NO3-). But BACTERIA & … can…

  6. Nitrogen Fixation (N2 --> NH3 or NH4+) Nitrogen Fixation (N2 --> NH3 or NH4+) • HOW? Biological or Environmental or Humans • BIOLOGICAL: Bacteria (called Nitrogen-fixing bacteria)These bacteria form symbiotic relationships with host plants. The bacteria live in nodules found in the roots of the legume family of plants (e.g. beans, peas, and clover) • Ammonia NH3 video HOW? Biological or Environmental or Humans BIOLOGICAL: Bacteria (called Nitrogen-fixing bacteria)These bacteria form symbiotic relationships with host plants. The bacteria live in nodules found in the roots of the legume family of plants (e.g. beans, peas, and clover)

  7. Nitrogen Mineralizationalso called AmmonificationOrganic N --> NH4+ • Decay of dead things, manure, etc. • Done by decomposers (bacteria, fungi, etc.) • During this process, a significant amount of the nitrogen contained within the dead organism is converted to ammonium (NH4+).

  8. NitrificationNH3 or NH4+--> NO2- --> NO3- (Nitrifying) Bacteria add oxygen to nitrogen in two steps: • STEP 1: Bacteria take in NH3 or NH4+& make NO2- = nitrite • Step 2:Bacteria take in NO2- & make NO3- = nitrate

  9. DenitrificationNO3- --> N2 (Denitrifying) Bacteria do it. Denitrificationremoves nitrogen from ecosystems, and converts it back to atmospheric N2.

  10. Nitrogen Fixation (N2 --> NH3 or NH4+) How?BIOLOGICAL • In aquatic environments (like fishtanks), blue-green algae (cyanobacteria) is an important free-living nitrogen fixer.

  11. Nitrogen Fixation (N2 --> NH3 or NH4+) ENVIRONMENTAL High-energy natural events which break the bond N2 Examples:lightningforest fireshot lava flows

  12. Nitrogen Fixation Atmospheric Nitrogen is broken into useable nitrogen (NH3 or NH4+)

  13. Human Impact Some forms of nitrogen (like NO3- and NH4+) can also enter the atmosphere to become: • smog- nitric oxide (NO) • Greenhouse gas- nitrous oxide (N2O) • Acid Rain-(nitrogen oxides)

  14. Human Impact • FERTILIZERS! • Extra nitrogen fertilizer can runoff, where it contaminates surface water or infiltrates into ground water. • In drinking water, excess nitrogen can lead to cancer in humans and respiratory distress in infants.

  15. Human Impact • In surface waters, extra nitrogen can lead to nutrient over-enrichment. • This leads to • fish-kills, • harmful algal blooms, • and species shifts in aquatic and land ecosystems. Eutrophication

  16. Yellow arrows indicate human sources of nitrogen to the environment. Red arrows indicate bacterial transformations of nitrogen. Blue arrows indicate physical forces acting on nitrogen. And green arrows indicate natural, non-microbial processes affecting the form and fate of nitrogen.

  17. In most ecosystems nitrogen is primarily stored in living and dead organic matter. This organic nitrogen is converted into inorganic forms when it re-enters the biogeochemical cycle via decomposition. Decomposers, found in the upper soil layer, chemically modify the nitrogen found in organic matter from ammonia (NH3 ) to ammonium salts (NH4+ ). This process is known as mineralization and it is carried out by a variety of bacteria, actinomycetes, and fungi. • Nitrogen in the form of ammonium can be absorbed onto the surfaces of clay particles in the soil. The ion of ammonium has a positive molecular charge is normally held by soil colloids. This process is sometimes called micelle fixation (see Figure 9s-1). Ammonium is released from the colloids by way of cation exchange. When released, most of the ammonium is often chemically altered by a specific type of autotrophicbacteria (bacteria that belong to the genus Nitrosomonas) into nitrite (NO2- ). Further modification by another type of bacteria (belonging to the genus Nitrobacter) converts the nitrite to nitrate (NO3- ). Both of these processes involve chemical oxidation and are known as nitrification. However, nitrate is very soluble and it is easily lost from the soil system by leaching. Some of this leached nitrate flows through the hydrologic system until it reaches the oceans where it can be returned to the atmosphere by denitrification. Denitrification is also common in anaerobic soils and is carried out by heterotrophicbacteria. The process of denitrification involves the metabolic reduction of nitrate (NO3- ) into nitrogen (N2) or nitrous oxide (N2O) gas. Both of these gases then diffuse into the atmosphere.

  18. Almost all of the nitrogen found in any terrestrial ecosystem originally came from the atmosphere. Significant amounts enter the soil in rainfall or through the effects of lightning. The majority, however, is biochemically fixed within the soil by specialized micro-organisms like bacteria, actinomycetes, and cyanobacteria. Members of the bean family (legumes) and some other kinds of plants form mutualistic symbiotic relationships with nitrogen fixing bacteria. In exchange for some nitrogen, the bacteria receive from the plants carbohydrates and special structures (nodules) in roots where they can exist in a moist environment. Scientists estimate that biological fixation globally adds approximately 140 million metric tons of nitrogen to ecosystems every year.

  19. The activities of humans have severely altered the nitrogen cycle. Some of the major processes involved in this alteration include: • The application of nitrogen fertilizers to crops has caused increased rates of denitrification and leaching of nitrate intogroundwater. The additional nitrogen entering the groundwater system eventually flows into streams, rivers, lakes, and estuaries. In these systems, the added nitrogen can lead to eutrophication. • Increased deposition of nitrogen from atmospheric sources because of fossil fuel combustion and forest burning. Both of these processes release a variety of solid forms of nitrogen through combustion. • Livestock ranching. Livestock release a large amounts of ammonia into the environment from their wastes. This nitrogen enters the soil system and then the hydrologic system through leaching, groundwater flow, and runoff. • Sewage waste and septic tank leaching.

  20. The nitrogen cycle represents one of the most important nutrient cycles found in terrestrial ecosystems (Figure 9s-1). Nitrogen is used by living organisms to produce a number of complex organic molecules like amino acids, proteins, and nucleic acids. The store of nitrogen found in the atmosphere, where it exists as a gas (mainly N2), plays an important role for life. This store is about one million times larger than the total nitrogen contained in living organisms. Other major stores of nitrogen include organic matter in soil and the oceans. Despite its abundance in the atmosphere, nitrogen is often the most limiting nutrient for plant growth. This problem occurs because most plants can only take up nitrogen in two solid forms: ammonium ion (NH4+ ) and the ion nitrate (NO3-). Most plants obtain the nitrogen they need as inorganic nitrate from the soil solution. Ammonium is used less by plants for uptake because in large concentrations it is extremely toxic. Animals receive the required nitrogen they need for metabolism, growth, and reproduction by the consumption of living or dead organic matter containing molecules composed partially of nitrogen.

More Related