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PRODUCTIVITY OF ECOSYSTEMS

Readings and References         Link to a very useful chapter on productivity

DEFINITIONS:
Productivity - energy fixed/area/time

NOTES

A. Photosynthesis - light energy is captured in two steps (the light-dependent and the light-independent [=dark] reactions) and stored as chemical energy (food)

carbon dioxide + water + energy yields glucose (sugar, stored chemical energy) + oxygen

6CO2 + 6H2O yields C6H12O6 + 6O2

264g + 108g (energy input ~ 700Kcal )180g + 192g

B. Requirements for photosynthesis

1. Water, carbon dioxide

2. Energy - light

3. Photosynthetic pigments

chlorophyll absorbs red and violet

carotenoids absorb blue & green

erythrin pigments red algae - in ocean green light goes deepest

4. Enzymes (protein molecules acting as catalysts)

5. Nutrients (coenzymes, etc.) magnesium in chlorophyll

C. Factors influencing rates of photosynthesis

1. Temperature

maximum rate at 30-35oC (90oF)

rate near zero at 50oC (120oF)

2. Water - land plants: 500g water/gm glucose synthesized (less for C4 and CAM plants)

transpiration - water loss through leaves

drought major factor

freezing limits water availability

3. Nutrients - on land, phosphorus, nitrogen, or N/P ratio

in ocean, iron and silica - low solubility and sinking problems

4. Light - in ocean compensation depth few cm to 100m

daylength on land and sea, but all places get same total illumination time over a year

saturation at 30% full sunlight (10% for leaf perpendicular to light)

photorespiration - like zapping your motherboard - too many electrons

C3 vs C4 plants and CAM plants

maximum use is 1-5% full sunlight if conditions are good

5. Difference between short and long term factors limiting productivity:

carbon dioxide may limit rate on summer day in moist, fertile cornfield

over a whole summer, water and nutrients limit

D. WORLD PRODUCTIVITY ESTIMATES

From Whittaker, R.H. 1975. Communities and Ecosystems, Ed. 2. New York. Macmillian Publ. Co. 385pp.

to convert to Kcal, multiply by 4.5

ECOSYSTEM TYPE

NPP (grams organic matter per M2 per year)

World total

 

Mean

(109metric tons/yr)

Tropical rain forest

2200

37.4

Tropical seasonal forest

1600

12.0

Temperate evergreen forest

1300

6.5

Temperate deciduous forest

1200

8.4

Boreal forest

800

9.6

Woodland and shrubland

700

6.0

Savanna

900

13.5

Temperate grassland

600

5.4

Tundra and alpine

140

1.1

Desert and semidesert

90

1.6

Extreme desert, rock, ice

3

0.07

Cultivated land

650

9.1

Swamp and marsh

2000

4.0

Lake and stream

250

0.5

TOTAL LAND

 

115

Open ocean

125 (180)

41.5 (60)

Upwelling zones

500

0.2

Continental shelf

360

9.6

Algal beds and reefs

2500

1.6

Estuaries

1500

2.1

TOTAL OCEAN

 

55.0 (75)

E. Non-photosynthetic production

    Deep sea hydrothermal vents - chemosynthesis (chemoautotrophy)
    Lithosphere, sediments

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