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

Controls on Net Primary Productivity

Nutrients

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

Multiple or co-limiting factors – often it is more Complex than Liebig’s Law of the minimum

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

Eucalyptus in Hawaii

January 1999, 55 months after planting

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

160

Nitrogen containing Compounds

N2 – nitrogen gasNO3 – nitrateNO2 - nitrite NH4 – ammoniumNH3 – ammoniaN2O – Nitrous OxideOrganic Nitrogen –Living and dead plantsAnd animals