nutrient cycling

lecture 40

carbon

• all important macromolecules contain carbon

• CO2 in atmosphere: of volcanic origin

• atmospheric carbon incorporated in photosynthesis

• heterotrophs gain carbon by consuming autotrophs, other heterotrophs, their remains, waste

where is most carbon found?

• in soils, rocks, marine sediments, dissolved in ocean water

• early land plants fixed carbon by photosynthesis

  • sugar for metabolism, cellulose for cell walls

• evolution of vascular tissue: ability to synthesize lignin

what happened during Carbonifeorus period?

• when vascular plants died, wood did. not decay (no decomposer had enzymes that could break down lignin)

lignin

• makes cell walls very strong and undigestible

what can break down lignin?

• only white rot fungus can break down lignin

what does brown rot fungus do?

• can work around lignin and digest the cellulose of cell walls

when did the capacity to digest lignin appear?

at the end of the Carboniferous period (300 mya)

what do plants remove from the atmopsphere

CO2

what is CO2, what does it affect, and how does it enter the atmosphere?

• it is a greenhouse gas

• affects climate

• and its released from burning fossil fuels

why was glaciation high when CO2 levels were low?

because CO₂ is a major greenhouse gas, and low CO₂ weakens Earth’s ability to retain heat. But CO₂ isn’t the only factor

Causes of periodic mass extinctions

• high CO2

  • greenhouse effect warmed Earth

  • stopped global conveyer belt

  • nutrients no longer distributed

  • massive die-off in oceans

  • decomposition resulted in release of H2S

    • H2S is toxic to animals and plants

fossilized remains are rich in what?

• carbon

How was CO2 released back into the air

• burning of fossil fuels

How has an increase in CO2 affected plants?

• plants have been growing faster

• they are converting 31% more CO2 into organic compounds compared to before the Industrial Revolution

COS

• carbonyl sulfide

• found in air bubbles in Antarctic ice

• can be used as a tracer for photosynthetic carbon fixation

  • carbonic anhydrase (binds CO2, CO equally)

what happens to COS levels as photosynthesis rates increase

COS levels decrease

what happens to carbon that is in the atmopshere?

• diffuses into oceans

• stored as carbonate, bicarbonate ions

• mainly stored in oceans

ocean acidification

• most of CO2 back returned into atmosphere by burning of fossil fuels, becomes dissolved into the ocean

• It’s used by photosynthetic phytoplankton (remove C from water)

• Marine organisms incorporate C (+ Ca2+) in shells, sediment

pH affects on marine life

• formation of shells rely on Calcium carbonate with near saturating levels of CO3-2

• CO2+H20—>H2CO3

• carbonic acid dissolves to form bicarbonate ions (HCO3-) a bade and H+ ions (acid): ocean acidification

• carbonate ions in seawater act like an antacid to neutralize the H+, forming more bicarbonate

Nitrogen cycle

• all require nitrogen, only some prokaryotes can use atmospheric N2

• N is the mineral element most found limiting primary production

In what forms do plants use nitrogen

• NH4, NO3, NO2 to make amino acids

what is the Haber-Bosch process?

• industrial N fixation (higher temps, pressures)

• synthesizing ammonia (NH3) from atmospheric nitrogen (N2) and H2

explain the biological nitrogen fixation

• nitrogen in fertilizer —> very soluble; easily washed off agricultural fields, enters stream, rivers

• pools in lakes, oceans

• N2O from fertilizer enters atmosphere, also a greenhouse gas

nutrient pollution

• low N limits growth of algae in fresh and marine waters

• fertilizer run-ff stimulates algal growth

• when algae use up all nitrogen, they die

• algae decomposed by aerobic bacteria, depleting oxygen dissolved in water

• other aerobic organisms suffocate

Describe eutrophication

• excess nutrients cause massive algae blooms

• when the algae die, aerobic bacteria decompose them, consuming vast amounts of dissolved oxygen, leading to hypoxia (low oxygen) or anoxia (no oxygen)

• creating "dead zones" that suffocate fish and other aquatic life, causing massive die-offs and disrupting ecosystems. 

sulfur

• amino acids cys and met contain S

• all protein synthesis require S

• sulfur in soil, seawater; taken up by primary producers

• burning of fossil fuels releases S into atmosphere

• increases cloud cover, reducing photosynthetic rates

• combustion —> N and S in atmopshere

• react with water to form acid found in rain

• acid rain: damages leaves

phosphorus

• nucleic acids require P

• most P is in rocks- phosphate salts, deep sediments (geologic cycling is slow)

• limits growth

• less soluble than N, adheres to soil

• can also cause eutrophication