Lec 9 Biogeochemical cycles

• A 

  • Most ocean doesn't have sunlight -> no photo -> biggest limiting availability 

  • No mention of photic 

    • Nutrient would be more limiting then 

What are global biogeohemical cycles?

• linked network of biological and physical processes that moves nutrients through pools within the environment

• Nitrogen, phosphorus, carbon -> from food sources -> get them from plants 

• Cycle impacts how available they are to living organism 

What are pools?

• large reservoir of nutrients (e.g., oceans, atmosphere, soil)

• Reservoir that is not moving 

• Not being used by living  

What is flux?

• movement of nutrients between pools

  • evaporation & precipitation

  • carbon-fixation through photosynthesis & respiration

• Examples

  • Taken out of atmosphere -> moves into soil 

  • Nitrogen movement 

  • Take atmospheric carbon -> plants make starchs -> moved = flux 

How can nutrients be moved?

• Nutrients can be carried long distances by winds as gases and particles

• by waters of streams and oceans as dissolved solutes or as particles

• Phosphorus in form of Phosphate lost in ground water washed downstream 

What is residence time?

• Residence time: how long the molecules stays in one pool 

What is the residence time in the hydro cycle?

• Ice sheet: maybe 20k years frozen 

• Atm: evaporated -> only in atm for couple of days before being rained out 

What is the hydrological cycle?

• Most rain and show made from evap of oceans 

  • Evapotranspiraiotn can also make rain 

• The biggest pool is the ocean (contains ~97.5% of earth’s water).

• Only 0.08% of global water is in flux at any given moment.

What happens as the Earth gets hotter?

• Heat Earth -> Ocean hotter -> more evap -> speeds up water cycle -> more powerful hurricanes , cyclones, more frequent -> more flooding 

  • Speed up water cycle -> more water natural disasters 

What are the major pools for the global carbon cycle?

• Major pools include atmosphere, oceans, land surface (soils and vegetation), sediments and rock

• Sediments and rock → 99% of global C

  • largest pool, acts as carbon sink

• Ocean and rock big reservoirs 

  • Most are in the atmosphere (atmospheric cycle – where most fluxes happen where it moves out and in) 

  • Once in pools -> could be there for a long time 

What is the difference between human fluxes and natural carbon fluxes?

• Orange: human fluxes and much smaller -> don’t move as much carbon as natural fluxes 

  • Uneven (only .5 out, more in atm) -> actions not in balance 

• Atmosphere thorough living organism  (green arrow) = photo 

  • Return carbon to atmosphere: cellular resp 

  • 200 Gt moving in and out of atm 

  • Even each other out 

How does the carbon cycle change anually?

• Record of atmospheric CO2 levels, as measured from Mauna Loa, Hawaii, from 1950s to 2010s

  • Above trees -> not getting atm averages from no local sources (houses etc) 

  • Inc in carbon in atm 

• Annual pattern with seasonal oscillations

  • highest in early spring

  • lowest in early fall

• 47 billion metric tons of CO2 enters and leaves atmosphere every year due to this annual pattern

• Respiration fairly constant, photo is not  

• Atm high in april 

  • No leaves -> carbon increases 

• Lowest in sept oct 

  • Trees active -> carbon levels decrease 

• Matches northern hemisphere (where most land is found) -> cycle driven by big land plants 

  • Partly offset by southern hemi, but it has less land 

How is Photo and respiration related?

• Photosynthesis and respiration typically equalize each other across year

  • same amount of CO2 taken out of atmosphere as enters it because of these processes

• Photo: uses sunlight to reduce CO2 + oxidizing O2

• Resp: same reaction in reverse

• form cycle

Where is more land?

• There is more land in the north

• More land in North with more seasonal tropical forests ->  

How has CO2 levels increased?

• atmospheric CO2 levels increased by more than 30% in 60 yrs

• If atmospheric CO2 levels have increased, then CO2 entering the atmosphere must exceed CO2 leaving it.

How does carbon dioxide enter the atmosphere?

• Geological inputs (volcanoes, mid-ocean ridges)

  • Volcanic release methane, CO2 

• MOR: hydrothermal vents 

• Biological inputs

  • respiration

• Anthropogenic inputs (burning fossil fuels, deforestation)

  • Burning fossil fuel and deforest 

    • Both contain carbon 

How does carbon dioxide leave the atmosphere?

• Geological removal

  • chemical weathering → CO2 in rainwater reacts with exposed rocks

• Biological removal

  • photosynthesis

What is BIOLOGICAL INPUT/REMOVAL or the terrestrical carbon cycle?

• CO2 in atm → photo → primary produces that fix CO2 into organic carbon → primary consumers feed on primary producer → secondary consumer

• aerobic resp + anarobic resp from decomposers in soil that feed on organic detritus

• Co2 comes out atm and goes back to atm 

• Examples

  • Co2 -> plant -> decomp -> release to atm 

  • Co2 -> plant -> eaten -> poop or die -> decomp  

    • Giraffe breath it out 

  • Anything in soil gets decomp -> released back into atm 

  • Sometimes goes to sediments -> can stay for awhile 

  • In food webs release to atm 

What is the biological input and removal marine carbon cycle?

• Open ocean: planktonic algae and cyanobacteria are major primary producers → protists and small planktonic animals are primary consumers that feed on primary producers → fisher and other secondary consumers more carbon through food webs → bacteria decompose organic matter and →. serves as food for other organisms

• Lose it to ocean sediments 

  • Deeper oceans where its colder in form of organic matter or methane -> methane can freeze -> stays there 

  • Get into sediments as carbon -> come back through food webs from upwelling -> move btwn water and atm 

    • Carbon stored as acid in water 

What can happen with warming temperatures in the ocean?

• Lose it to ocean sediments 

  • Deeper oceans where its colder in form of organic matter or methane -> methane can freeze -> stays there 

  • Great dying (shut down of gulf): world gets hot -> ocean gets hot -> methane becomes gaseous methane -> greenhouse gas -> even more warming  

    • Worst mass extinction event we know of 

Is the increase in CO2 unusual?

• Co2 levels change over time 

• Glacial ice as it forms → traps air bubble → ice can last for thousands of years → examine ice cores to find out what the atmosphere was like in the past.

  • High: greenhouse conditions 

  • Low: ice house (where we are) 

    • Holes that are frozen -> dig in ice caps (ice forms anually and layers) -> look for air pockets -> graph 

• Graph 

  • Large increase from 1950 

  • Something changes 1700s-1900s: humans started using fossil fuels 

What are the isotopes of carbon?

• 12C - 99% of all carbon

• 13C - ~1% of all carbon atoms

• 14C - 1 ppt (part per trillion) of all atmospheric C

  • unstable → decays to 14N

Was this increase in CO2 from human activities?

• Atmospheric carbon levels have increased, but the ratio of 13C to 12C has declined.

• Source of excess carbon is 13C depleted compared to carbon originally in the atmosphere

• Match concentration to source 

• C14 is not stable -> radiodecays (use for carbon dating) 

  • Die -> stop taking in C14 -> decays 

• Blue line: carbon levels have inc 

• Red line: source that is 13C depleted 

  • 12/13 ratio has decreased over tie -> doesn't match atm 

• Summary

  • Atmospheric CO2 increasing, but natural ratio of 13C/12C ratio is declining (can’t use 14C because it decays) is decreasing → CO2 must be coming from another source

How is carbon used in plants?

• plants preferentially incorporate 12C (over 13C) into biomolecules

• Organic matter contains a higher proportion of 12C as a result

• Plants 13/12 ratio differ from atm 

  • Less 13 than expected from the ratio in atm 

What kind of carbon is found in nonorganic sources?

• carbon released from other sources (volcanic gasses or dissolved seawater) has higher proportion of 13C

• sources do not match the isotopic ratio of excess carbon

  • too little 13 C in atm

What does the mismatch in inorganic carbon sources mean?

• neither volcanic gases nor dissolved ocean waters have 13C/12C rations that mach the increase in atm carbon

• If came from volcanoes or upwelling etc -> 13/12 ratio should inc 

  • More 13 in atm  

  • Doesn't match  

• Line matches plants 

  • Plants alive today 

  • Plants that died in carboniferous -> fossil fuels 

What can 14C be used for?

• living organisms continually incorporate 14C into their bodies throughout life

• 14C decays to other forms of carbon

• organism dies → amnt of 14C in body decays over time → radiocarbon date fossils

• 14C ratio 

• Comes from source that 14C depleted -> old plants 

  • Land just started to colonize -> fell in hypoxic bogs -> turned into fossil fuels 

Is this source modern or from fossil fuels?

• Additional studies showed that carbon entering in the atmosphere was 14C-depleted → modern plant vegetation contains too much 14C to be the source

• Ancient organic matter (coal, petroleum, natural gasses) → isotopically similar to carbon entering atmosphere

• Inc in Co2 is b/c of burning of fossil fuels 

  • Also from deforestation, but lesser 

• Carbon in atm is anthro 

How much carbon pollution do humans create?

• HUMANS PRODUCE 9 GIGATONS (1 billion metric tons0 OF CARBON POLLUTION ANNUALLY

• Photosynthesis and respiration move far more carbon in/out of atmosphere annually than we do

• However, our flux is largely unidirectional, and photosynthesis and respiration generally offset each other

  • don’t move as much carbon in and out as others -> humans largely unidirectional 

  • Burning fossil fuels in biggest cause 

What anthro activities that add carbon?

• ~20% à land use changes (deforestation, agriculture)

• ~80% à burning fossil fuels

• Not all ending in atm -> carbon stored in ocean water (deep oceans) -> eventually rise to surface and released into atm 

  • Carbon come out of ocean eventually 

What is the nitrogen cycle related to?

• This cycle is closely linked to the carbon-cycle because nitrogen is a critical component of amino acids, nucleic acids, membranes

What is the largest N2 pool?

• The largest nitrogen pool is N2 gas

  • form not usable by most living organisms

    • usable by chemoautotrophs

What is nitrogen fixation?

• process by which some bacteria and archaea reduce N2 gas to biologically useful NH3

  • this is how nitrogen enters food webs

• N2 taken out of atm into ammonium  

What is assimilation?

• process by which primary producers obtain biologically useful nitrogen from surroundings (NO3 - or NH3)

• take useful forms of nitrogen from soil or mutualistic that gets it from soil

What is denitrification?

• a form of anaerobic respiration in which NO3 - is terminal electron acceptor

• N in form of higher energy to lower energy 

What is nitrification?

• a process in which NH3 or NO2 - are oxidized to generate energy

Why does nitrogen need to be fixed?

• hemoautotrophic bacteria and arachaeons use NO3 - or NH3 to generate energy → releasing N2 gas as biproduct.

• This causes biologically useful forms of nitrogen to decrease in the soil.

• To obtain more, nitrogen fixers convert N2 gas into more NO3 - or NH3

• Essentially, they do it because this is how they generate their own energy.

What is anamox?

• Driven by chemoautotrophs to generate energy -> take it and go back to N2 gas 

  • Other organisms take before they can get to it 

What is the nitrogen cycle?

• Plants -> organisms -> back into soil (plants use ammonia) -> return to atm 

• Nitrogen fixation converts N2 → form that can be used by plants

• primary producers assimilate biologically usable N from soil or symbiotic N- fixing bacteria

• consumers obtain N from their food

• decomposer return N to soil as ammonia

• in Anoxic envi. some decomposing bacteria use NO3 - in resp → denitficiation (converts biological usable N back to N2)

• Chemoautotrophic bacteria gain the energy needed to fix carbon by oxidizing NH3 using O2 (nitrificatoin) or NO2- (anammox)

How do plants get nitrogen?

• biologically useful forms of N can be in low supply, especially in young soils

• plants can trade carbs with mutualists to obtain organic forms of the N they require

  • Lots of systems are nitrogen limited because most are in a form only chemotropic organism can use 

    • Very young soils are nitrogen limited b/c they don't have the organisms 

      • Form mutualists with chemoauthropic organisms 

    • Already source of nitrogen -> convince mutualist (fungi) to get it  

      • Soil releases carbohydrates into soil -> fungi hyphae grow towards carbs -> form mutualistic relation 

• Mutualists: can provide to N plants

  • Rhizobium bacteria

  • Ectomycorrhizae

What is the Rhizosphere?

• soil layer surrounding actively growing roots, receives carbohydrates from plants to stimulate growth of soil microbial mutualists

What are Rhizobium bacteria?

• nitrogen-fixers that exchange organically useful forms of N for carbohydrates

What is Ectomycorrhizae?

• fungi that exchange water and nitrogen (obtained from soil) for carbohydrates

• already have nitrogen -> fungi move it toward plant 

  • Can protect plant form pathogens 

How does mutualism with rhizobial bacteria work?

• Nitrogen fixing bacteria in the soil multiple in the rhizosphere in response to chemical signals from the plant roots

• plants that form mutualisms with these bacteria are often referred to as nitrogen fixers

  • but, it is the bacteria that are doing the work

• nitrogen fixing bacteria multiply outside root in response to signals → enter the root through a root hair or break in the epidermis → bacteria take up residence in a root nodule formed by dividing root cells

  • sugars in soil -> bacteria multiply -> plants grows around them and gives them carbs -> bacteria keep fixing nitrogen and give to plants 

  • Rare mutualism  

How does mutualism with ectomycorrhizal fungi work?

• fungi produce a thick sheath of fungal cells that surround plant root tips and extend into root interior

• fungal cells produce network of filaments that surround root cells → but do not penetrate them

  • Fungi grow hyphae quickly and move soil easily -> increases volume that plant can extract nutrients 

• fungi can provide root cells with N (obtained frmo soil) in exchange for carbs

• In soli with nitrogen already (lots of decomp that releases ammonia and nitrogen fixing bacteria) 

Why are mutualisms formed with mycorrhizae?

• fungi can decompose organic matter to obtain nitrogen (good at obtaining other nutrients from soils)

• hyphae are extensive → increases volume where nutrients are obtained

• Some fungi form mutualisms with nitrogen-fixing bacteria to obtain N for themselves and their plant mutualists

Where does mycorrhizae cover?

• Each colour represents a different type of mycorrhizal association

• Evolved ind multiple times -> covers most of land 

• D

What is the phosphorus cycle related to?

• Cycle is closely linked to the carbon-cycle because phosphorous is a key element for growth (nucleic acids and membranes, ATP)

What are the largest pools for phosphorus cycle?

• Rocks & ocean sediments → largest pools, P atoms leave pools via uplift & chemical weathering

How does the phosphorus cycle work?

• P enters food webs as PO4 3- , which is highly immobile in clay soils → hard for plants to obtain without help from mutualistic fungi

  • Enter as phosphate that are hard to move and hard for plants 

    • Mutualisms with fungi 

• P leaves terrestrial ecosystems through soil erosion, leaching, and groundwater runoff, and marine ecosystems through sedimentation

  • Sedimentary cycle (not a lot in atm) 

    • Phos moves to water -> goes into rocks 

• Leached from soils into ground water -> down-stream -> ends in ocean sediments -> makes continental drift to make mountain -> moves back into land 

  • Can take over 100 millions years for a P atom to return to food webs once enters ocean sediments → coastal upwellings can considerably shorten this timing

  • Lost quickly  

    • Ocean sediments can return with upwellings 

    • Most time stays in sediments until ocean becomes land through cont drift and mechanically weathered again (and/or enter food web 

What are endomycorrhizae?

• fungi that penetrate root cells, but do not form visible structures outside of root cells after this

  • can make them hard to study.

• Instead, they form highly branched arbuscules that grow inside roots

• D 

  • Phto and respiration are the biggest carbon flux 

  • Humans only 9