Ecosystem Type Net Primary Productivity (kilocalories/meter2/year) Tropical Rain Forest 9000 Estuary 9000 Swamps and Marshes 9000 Savanna 3000 Deciduous Temperate Forest 6000 Boreal Forest 3500 Temperate Grassland 2000 Polar Tundra 600 Desert 200
Net Primary Productivity of Different Systems
* Kilocalories are what we call “Calories” in everyday usage
In addition to primary productivity being a major sink for atmosphericCO2, it is also the base of the food chain and allows humans and allOther creatures to live, and…
It takes a lot of primary production to support higher trophic levels!
Data from Whittaker, R.H. 1961. Experiments with radiophosphorus tracer in aquarium microcosms. Ecological Monographs 31:157-188
1. Carbone, C. & Gittleman, J.L. A common rule for the scaling of carnivore density. Science, 295, 2273 - 2276, (2002). 2.Enquist, B.J. & Niklas, K.J. Global allocation rules for patterns of biomass partitioning in seed plants. Science, 295, 1517 - 1520, (2002).
Every Kg of predator needs 111KgOf prey living in the same area for the System to stay stable
OK, so we need to know what control productivity both forGlobal climate and for organisms that live here (including humans!)
We saw that water and temperature are very important, and that thereIs a huge response to small change in water. But what about theNutrients we talked about on Tuesday? What affect do they have?
Examples:Light can limit productivity,
So can water, and
Certain nutrients too
Limiting Factors for Biological Productivity
- Plants never seem to be able to “fix”, or assimilate all
the carbon available to them – something is limiting production
- This is true both on land and in the ocean
CO2 rarely limits productivity
Only about 44% of the total Electromagnetic energy reaching the earth is in the correct wavelengths for use by plants (called PAR) and only 0.5% – 3% of that is used!
Temperature is a strongLimiting factor.
Although plants in colderareas are optimized forColder conditions
Water also is a strongLimiting factor.
Much steeper curve =A much stronger positiveReaction
i.e. a little water goes a long way!
If plants have enough water, enough sunlight, and are bathed in CO2, why don’t they “fix” more carbon, or grow more efficiently, faster, larger?
In 1840, J. Liebig suggested that organisms are generally limited by only one single physical factor that is in shortest supply relative to demand.
Liebig's Law of the Minimum
PhosphorusIs very often limiting in freshwater systems
What is happening here?Why doesn’t the line keepGoing up?
In 1840, J. Liebig suggested that organisms are generally limited by only one single physical factor that is in shortest supply relative to demand.
Liebig's Law of the Minimum
Now thought to be inadequate – too simple!
- complex interactions between several physical factors are responsible for distribution patterns, but one can often order the priority of factors
Multiple or co-limiting factors – often it is more Complex than Liebig’s Law of the minimum
Look what happens with the addition of N
As we’ve seen in the ocean and on land, nutrients are often limiting.
Why nutrients?
Needed for enzymes, cellular structures, etc.
Pretty much analogous to vitamins for humans
Soon as you meet the requirements for one, anotherends up being limiting
Nutrient elements needed for all life
C HOPKINS Mg CaFe run by CuZn Mo
Hydrogen
Carbon
Zinc
Molybdinum
OxygenCopper
Calcium
Phosphorus
Magnesium
Iron
Iodine
Potassium
NitrogenSulfur
Order of Importance of Nutrient Elements in Different Environments
On Land In Freshwater In the Ocean
1) Nitrogen 1) Phosphorus 1) Iron
2) Phosphorus 2) Nitrogen 2) Phosphorus
3) Potassium 3) Silica 3) Silica
Eucalyptus Carbon Budget (Tons C ha-1 yr-1)
05
101520253035404550
Control Always Fert
TBCA
Fertilization increased growth and respiration
Nutrient Inputs to Ecosystems
Important nutrients for life generally enter ecosystems by way of four processes:
(1). Weathering
(2). Atmospheric Input
(3). Biological Nitrogen Fixation
(4). Immigration
Red means humans have a huge impact on these processes
Nutrient Outputs from Ecosystems
Important nutrients required for life leave ecosystems by way of four processes:
(1). Erosion
(2). Leaching
(3). Gaseous Losses
(4). Emigration and Harvesting
Red means humans have a huge impact on these processes
INPUTSWeathering
Atmospheric Input
Biological Nitrogen Fixation
Immigration
OUTPUTSErosion
Leaching
Gaseous Losses
Emigration/Harvesting
Nutrient flux in Ecosystems
In well functioning ecosystems relatively small amounts ofNutrients enter or leave.
Most of what is needed comes from internal recycling!(true for all systems not just aquatic)
Excess Nitrogen Deposition – Too much of a good thing!
Because Nitrogen often limits plant growth humanshave gone to great lengths to use it as fertilizer
It is also a by product of all types of combustion
The net result is that we have altered the natural way that Nitrogen cycles more than we have any other element -including Carbon
In an undisturbed nitrogen cycle the element cycles veryEfficiently – it is valuable so not readily given up by biota
In an undisturbed nitrogen cycle the element cycles veryEfficiently – it is valuable so not readily given up by biota
But humans add HUGE amounts of Nitrogen to the ecosystem
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