Nutrient Cycles

Nitrogen and Phosphorus

WHY DO WE NEED NITROGEN??

– Nitrogen is needed to make up DNA and protein! • In animals, proteins are vital for muscle function.• In plants, nitrogen is important for growth.

NITROGEN

Nitrogen “stores”

Largest store = atmosphere (N2)

Also stored in....• Oceans• Organic matter (in soil)

NITROGEN

78% of the planet’s Nitrogen is N2 (atmosphere)

there are 3 main ways that nitrogen is made available to plants/ animals....

#1 – Nitrogen Fixation

– This is a process that changes N2 into forms that plants can use!

Happens in atmosphere.

..LIGHTNING!

Happens in soil, and in

water bodies

(nitrate) (ammonium)

Lightning provides the energy for

nitrogen to react with oxygen in the atmosphere!

Nitrogen-fixing bacteria in the soil can convert (“fix”) N2 to ammonium.

Usually live on roots of legumes

and other plants.

Rhizobium

Nitrogen-fixing cyanobacteria in water can also

do this!In the water

In the soil

Video

In the soil – are an example of SYMBIOSIS!! These bacteria grow on the root nodules of

legumes like peas. The plants provide sugars, while bacteria

provide nitrogen ions.

Nitrogen fixing

bacteria

#2 – Nitrification and #3- Uptake

In the soil, nitrifying bacteria convert:

NH4+ NO2

- NO3-

Nitrate can be taken up by plant roots!

(Uptake)

So, plants that don’t live with nitrogen fixing bacteria, can also get nitrogen from the soil.

The Nitrogen Cycle

How does N2 get back to the atmosphere?

Denitrification = changes NO3-

back to N2

This occurs in aquatic and land ecosystems by denitrifying

bacteria

• Excess nitrogen dissolves in water, enters the waterways, and washes into lakes and oceans.

The nitrogencompoundseventually becometrapped insedimentary rocksand will not bereleased againuntil the rocksundergo hundredsof years ofweathering.

The Nitrogen Cycle

• Human activities can also affect the nitrogen cycle.– Due to human activities, the amount of nitrogen

in the ecosystem has doubled in the last 50 years.– Burning fossil fuels and treating sewage releases

nitrogen oxide (NO) and nitrogen dioxide (NO2).• Burning also releases nitrogen compounds

that increase acid precipitation in the form of nitric acid (HNO3).

Acid rain damaged these trees

• Agricultural practices often use large amounts of nitrogen-containing fertilizers.– Excess nitrogen is washed away, or leaches, into

the waterways.• This promotes huge growth in aquatic algae called

algae blooms.• Algae blooms use up all CO2 and O2

and block sunlight, killing many aquatic organisms.• Algae blooms can also produce neurotoxins that

poison animals.

A nice summary...

• Phosphorus is essential for life processes in plants and animals.– Phosphorus is a part of the molecule that carries

energy in living cells = ATP (cellular respiration)!!

The Phosphorus Cycle

The Phosphorus Cycle• How do plants and animals use phosphorus?

Plants Animals (humans)

Developing healthy seeds,

root growth, and stem strength!

Developing healthy bones

(works with Ca to build bone

tissue)

Corn with a Phosphorus deficiency

Where do we find P?

• It is not stored as a gas in the atmosphere like C and N....

• P is stored in phosphate rock and sediments on the ocean floors

(Phosphates: PO43-,

HPO42-, and H2PO4

-)

How it gets from rock soil

Phosphorus is released from rock into the soil by a process called “weathering”

CHEMICAL PHYSICAL

Weathering = rock breaks down into smaller pieces. These pieces make their way into the soil.

-Acid rain - Chemical in lichens

-Wind, rain, freezing

The Land Cycle• Plants take up phosphate through

their roots• Animals eat the plants (get

phosphate)• Decomposers return it to the soil

The Aquatic Cycle

• Phosphate gets into the water by erosion, leaching, run-off

• Most settles at the bottom (turns into sediment)

• Some phosphate is taken up by aquatic plants

Geological Uplift• Mountains and hills are created when

rock gets “uplifted” • The earth’s crust folds (very slowly)

and deeply buried rock layers rise up

Mt. Everest is made of limestone that

must have originally formed on ancient

sea floor. It contains fossils of marine

creatures.

This is a rock in Scotland. Below the yellow line was once horizontal rock. It has been uplifted over time. It has now started to erode due to weathering.

Human Activity & the P Cycle

• We affect the P cycle by: – Mining phosphate rock (for

fertilizers and detergents)– Making fertilizers and

detergents (industrial waste)

– Applying fertilizer to land – Fishing (remove aquatic

organisms – small effect)

A Nice Summary

• Any significant changes to any of these nutrients (C, H, O, N, or P) can greatly affect biodiversity.– Carbon cycle changes contribute to climate change

and global warming.• Slight temperature fluctuations and changes in

water levels can drastically change ecosystems.• Changes influence other organism in the

food webs.

How Changes in Nutrient Cycles Affect Biodiversity

– Increased levels of nitrogen can allow certain plant species to outcompete other species, decreasing resources for every species in the food webs.

– Decreased levels of phosphorus can inhibit the growth of algae that are very important producers in many food chains.

How Changes in Nutrient Cycles Affect Biodiversity