Lecture 16 Flashcards
(24 cards)
Carbon reservoirs
- Includes atmosphere, land, oceans, sediments, rocks, and biomass
- Reservoir size and turnover time are important parameters in understanding the cycling of elements
Carbon cycle
- CO2 in the atmosphere is the most rapidly transferred carbon reservoir
- CO2 is fixed by photosynthetic land plants and marine microbes
- CO2 is returned to the atmosphere by respiration as well as anthropogenic activities
- Microbial decomposition is the largest source of CO2 released to the atmosphere
Methane hydrate
- Form when high levels of methane are under high pressure and low temperature
- Huge amounts of methane are trapped underground as methane hydrates
- Can absorb and release methane
- Fuel deep-sea vent ecosystems
Light reaction
The electrons are used generate energy (ATP) and reducing power (NADPH), as well as a useful byproduct O2
Dark reaction
ATP and NADPH are used to synthesize organic carbon from CO2
CH2O
Refers generally to organic matter (OM) and not to a specific compound
Aerobic respiration equation
CH2O + O2 –> CO2 + H2O
Oxygenic photosynthesis
The dominant form of primary production, produces enough oxygen to oxidize all the organic matter produced by photosynthesis
Anoxic habitats
Can vary in size and shape:
1) Some near the oxic world; intense aerobic heterotrophy in the top few mm of sediments stops oxygen from penetrating far, creating anoxic mud only mm away from oxic waters
2) Organic rich particles: anoxic microhabitats in otherwise oxic soils and waters
3) Bottom waters of lakes and oceanic oxygen minimum zones
Sulfate reduction
- Crucial in marine environments, where there is lots of sulfate
- Microbial process important for organic matter mineralization in anoxic environment
Carbon dioxide redution
- Crucial in freshwater environments, including wetlands and rice paddies, where sulfate is often in limited supply
- Microbial process important for organic matter mineralization in anoxic environment
Anaerobic food chain
1) Hydrolysis of biopolymers
2) Primary fermentation of monomers
3) Secondary fermentation
4) Methanogenesis
- Acetate and H2 are central compounds in aerobic decomposition
- Methane and carbon dioxide are the ultimate end products
Acetate and H2
- Central compounds in anaerobic food chain because:
1) Both can be produced by fermentation pathways
2) Also produced by another group of microbes in another step of the anaerobic food chain: the acetogenic bacteria (secondary fermenters)
Interspecies hydrogen transfer
Connection between a hydrogen gas producer (acetogen) and a hydrogen gas consumer (sulfate or carbon dioxide reducer)
Syntrophic
Mutually beneficial relationship where the organisms are physically very close together
Nitrogen
- 4th most abundant element (after: C, O, and H) in organic matter
- Its supply often limits growth and biomass of terrestrial and aquatic organisms (strongly linked to C cycle)
- Redox from -3 to +5: Electron acceptor and electron donor for energy metabolism
5 key microbial processes in the N cycle
- Nitrification
- Denitrification
- N2 Fixation
- Ammonification
- Anammox
1) Nitrogen fixation (N2)
- N2 = most stable form of nitrogen and major reservoir for N on Earth
- Reduction of nitrogen gas to ammonia
Diazotrophs
Nitrogen-fixing microbes:
- Phototrophs
- Chemotrophs
- Aerobic/anaerobic microbes
- Free-living/symbiotic microbes
- *No eukaryotic organism is known that can fix nitrogen
2) Nitrification
An aerobic two step microbial process in which ammonia is oxidized to nitrate sequentially by two distinct groups of chemolithoautotrophic bacteria :
1) Ammonia oxidizing bacteria and archaea (AOB and AOA)
2) Nitrite oxidizing bacteria (NOB)
Denitrification
- Oxidized N compounds are good electron acceptors
- NO3- reduction half reactions generate almost as much free energy as aerobic respiration
- Occurs where nitrate is present but O2 concentrations are reduced
Annamox
- Anaerobic ammonia oxidation
- Ammonia can also be oxidized under anoxic conditions through the annamox process
Human activity and imbalance
1) Development of industrial processses (Haber-Bosch) to reduce N2 to NH4+
2) Implementation of agriculture practices that boost crop yield
3) Burning fossil fuels
Consequences of fertilizer use
- Around 90% of N fertilizer is NH4+ nitrifying bacteria convert it to highly mobile NO3- which leaches into rivers, lakes, and aquifers
- Results in N loss and eutrophication of coastal waters, creating huge hypoxic zones around the world
