Ecosystem Metabolism 1:

Primary Production

• Population – distinct group of individuals of a species that live, interbreed, and interact in the same geographic area.

• Community – includes all of the populations of organisms that live and interact with one another in a given area at a given time.

• Ecosystem – consists of a self-sustaining, self-regulating community of organisms interacting with the physical (abiotic) environment within a defined geographical environment.

Levels of Integration:Landscapes

Ecosystems

Communities

Species

Populations

Individual Organisms

Organ Systems

Organs

Tissues

Cells

Subcellular Organelles

Molecules

Ecosystem Metabolism:

-requires constant energy input

Energy Flow in Ecosystems

Producers

Consumers

Decomposers

Two Laws of Thermodynamics

• First Law: Energy cannot be created or destroyed, but it can be changed from one form to another.

• Second Law: Energy cannot be changed from one form to another without loss of usable energy.

First law Second law

When energy transformations occur, energy is neither created nor destroyed (1st Law) but there is always loss of usable energy, usually as heat (2nd Law).

One Way Flow of Energy

Living Organisms Need Energy

• Autotrophs – gain energy from the sun and materials from non-living sources– Plants, algae, phytoplankton (primary producers)

• Heterotrophs – gain energy and materials from eating other living organisms– Herbivores eat plants (primary consumers)– Carnivores eat animals (secondary/tertiary consumers)– Omnivores eat both plants and animals

• Decomposers – gain energy and materials from organic material– Mushrooms, bacteria, some invertebrates

Photosynthesis:

CO2 (from

air)

H2O

O2 (to

air)

C6H12O6

Solar energy converted to chemical energy

CO2 converted to Carbohydrate

Solar energy + 6CO2 + 6H2O → C6H12O6 + 6O2

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Happy Rays of Sunshine

Overview of Cellular Respiration

• Cellular respiration is the step-wise release of energy from molecules (usually carbohydrates) used to synthesize ATP molecules.

• This is an aerobic process that requires oxygen (O2) and gives off carbon dioxide (CO2), and involves the complete breakdown of glucose to carbon dioxide and water:

C6H12O6 + 6O2 → 6CO2 + 6H2O + energy(in form of ATP)

• Primary production - the synthesis of organic matter by autotrophs– Always measured as a rate per unit of time

– Sugar cane farmers kg/ha/yr cane production

• To accumulate organic matter, photosynthesis must be greater than respiration

• Compensation point – when photosynthesis = respiration– No growth / no reproduction

Two Measures of Production

Gross Primary Production (GPP)

Energy (or carbon) fixed via photosynthesis per unit time

Net Primary Production (NPP)

Energy (or carbon) fixed in

photosynthesis – energy (or carbon) lost via respiration per unit time

=

=

NPP = GPP - RespirationYou need to know this

Primary Productivity

CO2

C6H12O6

Photosynthesis Respiration

Solar Energy

Heat Energy

Biomass (g/m2/yr)

O2

Available to Consumers

Chemical Energy (ATP)

NP

P

GP

P

Measuring Primary Production: Terrestrial

• Primary production measured as a rate per unit time

• Can measure CO2 uptake rate during the day = net production

• CO2 released at night = respiration

12H20 + 6CO2 + 2966kj (solar energy) C6H12O6 + 6O2 + 6H20

Energetic Equivalents

• Absorption of 6 moles of CO2 indicates that 2966kj of energy has been absorbed

• This gives us a relationship between carbon accumulated and energy gained

• We can determine the amount of carbon in a plant by measuring the amount of energy in that plant

Simple Method to Measure Primary Production: Harvest Method

B = biomass change in the community between time 1 (t1) and time 2 (t2)

• B1 = biomass at (t1)

• B2 = biomass at (t2)

B = B2 – B1

Harvest Method

• Whole plant, aerial production, or root production

• Two possible losses must be recognizedL = biomass losses by death of plants or plant parts

G = biomass losses to consumer organisms

• With those values:

NPP = B + L + G

Harvest Method Energy Determination

• NPP can be converted to energy by measuring the caloric equivalent of the material in a bomb calorimeter

Mean of 57 plant species

cal/g dry wt J/g dry wt

Leaves 4,229 17,694

Roots 4,720 19,748

Seeds 5,065 21,192Golly 1961

Aquatic Primary Production

• The most important primary producers in aquatic systems are phytoplankton– Single cell plants suspended in the water

column

• Estimate primary production by measuring gas-exchange using light bottle dark bottle– Light bottle determines oxygen produced by

photosynthesis – Dark bottle measures oxygen consumed by

respiration

Phytoplankton:

Light – Dark BottleMeasure initial oxygen concentration in both bottles

Place bottles in water for a specific period during the day

Measure final oxygen concentration in both bottles

LBI = initial O2 in the light bottle DBI = initial O2 in the dark bottle

LBF = final O2 in the light bottle DBF = final O2 in the dark bottle

GPP = LBF – DBF (Total oxygen produced)

NPP = LBF – LBI (Oxygen increase)

Respiration = DBI – DBF (Oxygen decrease)

GPP = LBF – DBF (Total oxygen produced)

NPP = LBF – LBI (Oxygen increase)

Respiration = DBI – DBF (Oxygen decrease)

LBI = 5.3 DBI = 5.3 LBF = 6.8 DBF = 4.2; 1 hr

GPP = LBF – DBF = 6.8 – 4.2 = 2.6 mg/L/hr

NPP = LBF – LBI = 6.8 – 5.3 = 1.5 mg/L/hr

Respiration = DBI – DBF = 5.3 – 4.2 = 1.1 mg/L/hr

NPP = GPP – Respiration = 2.6 – 1.1 = 1.5 mg/L/hr

What Does Production Actually Mean??

• More carbon fixed from the atmosphere = more food available

• The greater the productivity, the greater the biomass of heterotrophs that can be supported

How to Estimate Carbon Produced

• 1 mg/L O2 = 0.375 mg Carbon

• GPP = 2.6 mg O2/L/hr * 0.375 = 0.975 mg C/L/hr

• NPP = 1.5 mg O2/L/hr * 0.375 = 0.563 mg C/L/hr

• For this example, 0.563 mg of carbon per liter of water per hour are added as biomass to the system

Estimated NPPVegetation Type Annual net primary production

Ocean 48.5 46% of total production

Land

Tropical rainforests 17.8

Broadleaf deciduous forests 1.5

Broadleaf and needleleaf forests 3.1

Needleleaf evergreen forests 3.1

Needleleaf deciduous forests 1.4

Savannas 16.8

Perrenial grasslands 2.4

Broadleaf shrubs 1.0

Tundra 0.8

Desert 0.5

Cultivated areas 8.0

Total for land vegetation 56.4 54% of total production

Total for globe 104.9

Units = petagrams of carbon; 1 petagram = 1015 grams = 109 metric tons

Worldwide Production

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Ocean Productivity

• On a per square meter basis the oceans are about as productive as the arctic tundra– Sometimes called a biological desert

• However, because the ocean’s make up 71% of the Earth’s surface, they account for 46% of total productivity

Photosynthetic Efficiency

• Percentage of received solar energy a plant uses:

Energy fixed by primary production*

Energy input per unit area per unit time

Efficiency of GPP = X 100

*Calculate number of carbon atoms from plant weight. Can then calculate the amount of energy required to build the plant.

Efficiency of Lake Mendota, Wisconsin

20,991 kJ/m2/yr gross primary production

4,973,604 kJ incident sunlight

Efficiency of GPP = X 100 = 0.42%

Vegetation Type GPP Efficiency*

Forests 2.0 – 3.5%

Herbaceous Communities 1.0 – 2.0%

Crops < 1.5%

Phytoplankton Communities Usually < 0.5%

*NPP is even less efficient. Overall, terrestrial plants usually convert approximately 1% of incoming solar energy to NPP during the growing season.

• Depth of light penetration determines the photic zone:

Where:

l = amount of solar radiation (joules per m2 per unit of time)

t = depth

k = extinction coefficient

• Typically, more than half of the solar radiation is absorbed in the first meter of water:

Limiting Factors – Aquatic Communities

dldt = kl

Attenuation of Solar Radiation

Pure water

Oceanic seawater

Coastal seawater ~k=0.3

Mississippi River?

-Turbulence

Lake Classification Based on Production

• Eutrophic – high production but little light penetration

• Oligotrophic – low production but high light penetration

Rate of Photosynthesis Measured as grams of carbon fixed per m2

Note the scale

Eutrophic

Intermediate

Oligotrophic

Marine Communities

North Pacific Gyre

Euphotic Zone – the surface down to 1% light level

Nutrient Limited?

Why are the Ocean’s so Unproductive?

P – High; N – Low

Nitrogen, not phosphorous, is limiting

Surprising because of the ability of cyanobacteria to fix atmospheric nitrogen?

What else?

• Top down control – Predation (by herbivores) is actually limiting the phytoplankton population– Nutrients phytoplankton zooplankton fish– Herbivory limits phytoplankton

• Bottom up control – Some other nutrient than nitrogen or phosphorous may be limiting– Nutrients phytoplankton zooplankton fish– Nutrients limit phytoplankton

Sargasso Sea

• Found not to be N or P limited, but Iron limited

Nutrients added to experimental culture

Relative uptake of 14C by cultures

None (control) 1.00

N + P only 1.10

N + P + metals (excluding iron) 1.08

N + P + metals (including iron) 12.90

N + P + iron 12.00

Why Iron

• Cyanobacteria fix atmospheric nitrogen to a form available to phytoplankton

• Iron is necessary for this process:

Iron cyanobacteria N fixation phytoplankton

Nutrient Addition:303 studies combined

Silica important when community dominated by diatoms

Freshwater Production Limits

• Solar radiation usually limits primary production in a given freshwater lake on a day to day basis– Temperature is highly correlated to solar radiation, so it

is hard to tease out specific temperature effects

• Plants require nitrogen, calcium, phosphorous, potassium, sulfur, chlorine, sodium, magnesium, iron, manganese, copper, iodine, cobalt, zinc, boron, vanadium, and molybdenum– Any one of these could be limiting in a freshwater lake,

but is usually nitrogen and/or phosphorous– Ocean water usually has a constant amount of these

nutrients

Eutrophication

• Eutrophication – increase in phytoplankton density due to anthropogenic increases in nutrients– Usually shift from a diatom or green algae

dominated community to a blue-green algae dominated community

– To control eutrophication, you must control nutrient source

• Sewerage or runoff

Blue-green Algae Negative

• Can become very abundant when nutrients are abundant and form a floating ‘scum’– Zooplankton do not graze as heavily on blue-

green algae– Can fix their own N when it is limiting

• Low nutrient food item for zooplankton

Limited by Phosphorous

Phosphorous is limiting in this system, not nitrogen

More Phosphorous

Chlorophyll a increases as phosphorous increases

Nitrogen-to-phosphorous ratio can regulate the phytoplankton community; nitrogen limited

Aquatic Summary

• Phytoplankton dominates primary production

• Ocean primary production is nitrogen limited– Indirectly iron limited– Overall, ocean productivity is low

• Freshwater lake primary production is phosphorous limited– But can be limited by other nutrients– FW lake productivity can vary from highly

oligotrophic to highly eutrophic

Terrestrial Limits to Primary Production

• Solar Radiation– Equator to poles

• Temperature– Tropical mountains

• Rainfall

• Nutrients– Nitrogen, phosphorous

Using satellite imagery to estimate global primary production

(a) June 1988 – August 1998

Latitude & Solar Radiation

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Evapotranspiration

• Evapotranspiration – the amount of water pumped into the atmosphere by evaporation from the ground and via transpiration from vegetation– A measure of solar radiation, temperature and

rainfall

Can be used to predict above ground NPP

Vegetation Type

• Leaf – area index – The greater the surface area the greater amount of photosynthesis– Conifers (pine trees) have a

higher leaf-area index than deciduous trees (oak trees)

– Conifers keep their leaves much longer, thus they have a longer growing season

Warm Temperate Zone

Cool Temperate Zone

Leaf Area Duration

Leaf-area index times length of growing season (determined by temperature) in months. Accurately predicts GPP.

Another value used to describe temperature over time is degree day: the sum of daily average temperatures for a specific period.

Needle - leaves

Broadleaves

Nutrients Are Often Limiting

Like in aquatic systems, N and P can be limiting.

Competition can limit primary production

Year # species

1856 49

1862 28

1872 16

1903 10

1919 8

1949 3

Species diversity can affect primary production

Primary production can affect species diversity