Ecosystem ecology studies the flow of energy and materials through organisms and the physical
environment as an integrated system.
a population
reproductionthrough generations
resources
?
Ecosystem ecology divides the world into pools and fluxes of materials and energy:
N
N N
N
N
N
NNN N
N
NN
N
N
Pools are quantities of materials such as carbon & nitrogen, that are contained in certain subdivisions of the ecosystem.
They are measured in g or moles per m2.
Pool of all forms of N in living plant
biomass
Pool of inorganic N in the soil (NO3
and NH4).
N
Fluxes are rates of material transfer between pools, measured in g or
moles per m2 per day or year.
water vapor release
More live biomass
litter
O2 release
CO2 uptake
Absorbs light
Water uptake
Soil nutrient uptake:
N,P,S,K,…
root exudates (complex sugars, allelochemicals?,
leached N
Matter fluxes through a typical primary producer:
Matter fluxes through a typical primary consumer:
C, N, H2O, etc. in dung
C, N, H2O, etc. in milk
C, N, H2O, etc. in grass
C, N, H2O, etc. in the dead cow
C, N, H2O, etc. in a calf
C, N, H2O, etc. in urine
O2 of air intake
CO2 of air expelled
Methane, CO2
Scavengers: vertebrate carrion eaters,Seldom restricted to carrion.
Detritivores: invertebrate consumers of organic matter.
Decomposers: fungi and bacteria.
Matter fluxes through a decomposer, detritivore, or scavenger:
More decomposers, detritivores or scavangers
simpler organic waste
CO2 release
O2 uptake
C, N, H2O, etc in dead organic matter
C, N, H2O, etc. in the dead decomposer
Dead organic matter from
carrion, litter,
feces & urine
Net primary production:(the biomass produced by autotrophs)
Herbivores(primary consumers)
Scavengers,Detritivores &Decomposers
(primary consumers)
Carnivores I(secondary consumers)
Carnivores I(secondary consumers)
Carnivores II(tertiary consumers)
Carnivores II(tertiary consumers)
Generalized trophic web
is eaten by adds
Questions we can address only through ecosystem ecology:
“Budget questions” (How do all the fluxes and the changes in
pool size add up?)
• What happens to the portion of the nitrogen that is added to the
farmers field but is not harvested with the crop?
• What is the fate of CO2 expelled to the atmosphere from burning
fossil fuels?
• How much of the annual rainfall is returned to the atmosphere
via plant transpiration, soil evaporation, and how much goes to
groundwater?
“Comparative questions” (Why do ecosystems differ in pool sizes and
fluxes? What are the controls over ecosystem processes?)
• Why do ecosystems differ in the %carbon that sits in living
plants versus in the soil organic matter? (E.g. : tropical forests =
most carbon in biomass, tundra = most carbon in soil.)
• How does plant species composition and diversity affect the
productivity of grasslands and forests?
• How will climate change (=warmer temperatures, different
precipitation patterns) affect productivity and species diversity?
Questions we can address only through ecosystem ecology:
Climate Vegetation Feedbacks:
VegetationVegetation
amount and compositionamount and composition
Local weatherLocal weather
patternspatterns
Earth’s climate systemEarth’s climate system
Land Land managementmanagement
Changes in Changes in atmospheric atmospheric compositioncomposition
Energy and material cycles:
Solar energy drives:
• The hydrologic cycle
• The carbon cycle
• The nitrogen and most other mineral cycles
Earth Energy Balance
Hydrologic cycle
The Nitrogen Cycle
Carbon cycle
Global carbon pools and residence times
Photosynthesis:The rate of carbon assimilation per area of photosynthetic area.
6H2O + 6CO2 + light ----------> C6H12O6+ 6O2
respiration
O2 CO2
root exudates
new biomass
The rate of plant
respiration per unit area (Rp)
The rate of carbon fixation per unit area:
Gross Primary Production
(GPP) Net Primary Production
into the trophic web
Net Primary Production (NPP)
Net carbon gain in biomass(= total carbon absorbed by plants (GPP) – carbon released by
plant respiration Rp)
NPP is primarily controlled by precipitation and temperature:
DESRT: desertTUNDR: tundraWDLND: woodlandBOENL: boreal evergreen,
needle-leafedBODBL: boreal decciduous,
broad-leafedBODNL: boreal deciduous, needle-leafedGRSTE: temperate grasslandGRSTR: tropical grasslandTEDBL: temperate deciduous
broad-leafedTEENL: temperate evergreen,
needle-leafedTEEBL: temperate evergreen,
broad-leafedTRDBL: tropical deciduous,
broad-leafedTREBL: tropical evergreen,
broad-leafed
The major earth biomes differ in NPP with precipitation. A
bove
-gro
und
NP
P g
m-2 y
r-1
Global distribution of primary productivity
Net Ecosystem Exchange (NEE)
= Carbon absorbed or released by the entire ecosystem(GPP – ecosystem respiration)
The rate of ecosystem respiration (RP+Rs)
The rate of carbon/energy fixation: Gross
Primary Productivity
(GPP) Net Ecosystem Exchange
This is the carbon that stays in the
ecosystem.
The rate of ecosystem respiration (RP+Rs)
The rate of carbon/energy fixation: Gross
Primary Productivity
(GPP) Net Ecosystem Exchange
This is the carbon that comes out of the ecosystem.
Net Ecosystem Exchange (NEE)
= Carbon absorbed or released by the entire ecosystem(GPP – ecosystem respiration)
Carbon Sequestration:
The long-term storage of carbon in the terrestrial biosphere or the oceans, thus removing CO2 from the atmosphere.
(Negative fluxes indicate net CO2 uptake by the ecosystem)Data courtesy of Jim Heilman, Texas A&M and Marcy Litvak, University of New Mexico.
Net Ecosystem Exchange at Freeman Ranch
Net Ecosystem Exchange at Freeman Ranch
Grassland site
Woodland site
Transition site
(Freeman Ranch is taking up carbon)Data courtesy of Jim Heilman, Texas A&M and Marcy Litvak, University of New Mexico.
Cumulative ecosystem carbon gain