1

Energy Flows open system

sun earth

Nutrients cycle closed system

earth

poolpool

flux

flux

Classes of nutrients

Major nutrients: carbon,nitrogen, oxygen, water

Minor (but biologicallyimportant) nutrients:phosphorous, calcium,sodium , sulfur,magnesium, iron …

earth

poolpool

flux

flux

Types of transfer processes

Meteorological (rain, snow, wind)

Geological (volcanism, drainage)

Biological (transfers involving

microbes, plants or animals)

pool

earth

Nutrients cycle closed system

Pools =amounts

Fluxes =transfer rates

Rates of cycling

are dependenton pool sizesand flux rates

pool

flux

flux

Hydrologic cycle

The Amazon river

moves not onlywater, but nutrients

The Amazon river floods seasonally inundating 20% of theAmazon basin, depositing nutrients and enriching the soil

Many planned dams threaten thenatural flooding of the Amazon

2

The rich nutrientsmean the river isteeming with life

(high productivity) The sediment

laden waterselects foradaptationsin fish tosurvive inmurky water

pools = 1018 grams, fluxes = 1018 grams/yr

Hydrologic cycle

Evaporation from the sea (1/5th of all energy used to evaporate water)

Small atmospheric pool (13) Precipitation over sea (flux=283)

Flux to land (36=319-283) : flux into atmosphere must equal flux out

Large pool in ocean (1,380,000)

pools = 1018 grams, fluxes = 1018 grams/yr

Hydrologic cycle

Rainfall to land (95=36+59) : flux into atmosphere must equal flux out;evaporation from land contributes large fraction of rainfall to land

Runoff (36) balances 36 net which left oceans

Evaporation from land (flux = 59)

pools = 1018 grams, fluxes = 1018 grams/yr

Hydrologic cycle

Humans are altering the hydrologic cycle: a) 50% of the surface water is used by humans

(already a shortage, will get worse)

b) mining “fossil water” - pumping aquifers faster than they are beingreplenished (e.g. AZ and NV)

c) deforestation reduces evapo-transpiration and rainfall(50% of rainfall in amazon from evapo-transpiration)

Deforestation affects local rainfall - Panama

Forest cover in Panama

1910 1960 2010

Ra

infa

ll

3

Nitrogen cycle ( a simplified version)Nitrogen is one of the 2 most limiting plant nutrients

Inorganic nitrogen(nitrate and ammonium)

Atmospheric N2

Dead plants and animals

Organic nitrogen in proteins (live plants and animals)

1

2

4

3

Atmospheric N is a huge poolnot available to plants

1. Nitrogen fixation: <5% fixed bylightening, 95% by bacteria in soil orsymbionts, limiting step, expensive

2. Assimilation: rapid

small pool

3. Denitrification: bacteria convertorganic nitrogen back toelemental form

4. Many steps involving bacteria (some stepsare called ammonification and nitrification),slow step

Nitrogen fixation is the most limiting stepHumans now use fossil fuels to make fertilizerFertilizers have doubled the global input

Impacts of increasing nitrogen inputs : Mississippi

Humans have increase N input into the Mississippi by 8 fold in 50 yrs

7 million metric tons of N in fertilizer is applied in the river basin/yr1.8 million metric tons (26%) are lost down the river/yr = $750 million

This causes temporary algal blooms in the Gulf, which die, decompose

and deplete the water of oxygen, killing all other life

The “dead zone” in the Gulf is larger than the size of New

Jersey (20000 km2) and growing larger every year

Differences in the nitrogen cycle between temperate and tropical regions

Inorganic nitrogen(nitrate and ammonium)

Atmospheric N2

Dead plants and animals

Organic nitrogen in proteins (live plants and animals)

1

2

4

3

Distribution of nitrogen soil plants

Tundra 99% 1%Temperate 70% 30%Tropics 30% 70%

c) Leads to most nutrients being in the soil(dead plants) in cold climates and mostbeing in the live plants in warm climates

d) Deforestation in the tropics removes most ofthe nutrients, less impact in temperateforests

b) Decomposition (steps 3 & 4) are slow incold climates (experiment?)

a) Pool sizes differ. What steps arelimiting in the tundra?

Variation in nutrient availability

Andes are new and nutrient rich, as arethe rivers draining them (Amazon)

The Guyanashield is old,

highly weatheredand nutrient poor

Variation in nutrient availability

Black water river draining white sands (nutrient poor)

White-water river draining nutrient rich Andes

Burning for agriculture causes a pulse of nutrients, most of which are

washed downstream (majority of nutrients are in plants not the soil)

In white sands forests, plots sustain

agriculture for ~2 years before nutrientsare completely depleted and plotsabandoned

4

Despite nutrient poor soils (white

sands), forests grow very big.

How do they do it?

many adaptations to acquirenutrients and lose less

Plant adaptations for nutrient poor soils

Investments in roots, many at the surface

Plant adaptations for nutrient poor soils

Symbioses with nitrogen fixing bacteria and mycorrhizal fungi

Plant adaptations for nutrient poor soils

Carnivorous plants

Plant adaptations for nutrient poor soils

Defend the nutrients already acquired(toughness, secondary metabolites

such as tannins)

Tannins in leaves leach intothe water turning it dark

(black water rivers)

White sands are nutrient poor

Black water rivers are nutrient poor becausethey drain nutrient poor white sands

Plants on white sands are selected to be welldefended against herbivores (protect thenutrients)

Black water rivers are black becausethey are full of tannins leached from

the well defended leaves

Black water rivers have lower animal

abundance and diversity than white water rivers (nutrient rich)

White versus black water rivers