Ch 26. Nitrogen Cycle

Where is nitrogen the most abundant (biggest pool)?

Atmospheric N2

Put the steps of the nitrogen cycle in order

Out of order:
Mineralization
Fixation
Denitrification
Assimilation
Nitrification

Fixation (N2 —> NH4)
Nitrification (NH4 —> NO3)
Assimilation (NH4/NH3 —> Biological N)
Mineralization (Biological N —> NH4)
Denitrification (NH4 —> N2)

Which nitrogen cycle process?
Turning atmospheric N2 into ammonium
Performed by bacteria, lightning/wildfires

Fixation

Some plants (legumes) have root nodules that host Rhizobium bacteria, which perform which nitrogen cycle process?

Fixation

Hosting Rhizobium bacteria for fixation is especially helpful in

low-nutrient environments

What nitrogen cycle process?
Aerobic microbes turn ammonium —> NO3 (nitrate)

Nitrification

bacteria that perform nitrification are AKA

nitrifying bacteria

What nitrogen cycle process?
NH4/NO3 turned into producer tissues

Assimilation

What nitrogen cycle process?
Biological N is turned into inorganic N (NH4) in soils

Mineralization

For what process in the nitrogen cycle are decomposers most important?

Mineralization

What nitrogen cycle process?
NH4 in soils are turned back into atmospheric N2 gas

Denitrification

Bacteria that perform denitrification are AKA

denitrifying bacteria

Nitrification is (aerobic/anaerobic)
Denitrification is (aerobic/anaerobic)

Aerobic
Anaerobic

Since denitrification is anaerobic, we would expect it to occur in ____ waters or ____-____ soils

stagnant waters
oxygen-poor soils

Between N and P, terrestrial NPP is most limited by Nitrogen closer to the (poles/tropics)

Poles

Why is N-limitation greater in the poles than P-limitation?

Cold environment —> Slow decomposition —> Less N cycling

Why are Nitrogen-fixing trees not found in the poles, yet nitrogen is the limiting nutrient there?

N-limitation is not worth the trade-off of putting energy towards N-fixation

The balance of multiple chemical elements, and how element ratios affect and are affected by ecosystem processes

Stoichiometry (ecological)

50% of the world would not exist if it weren’t for what process?
(Food production)

Haber-Bosch process
(Synthetic N2 + H2 to make fertilizer)

Human activity disrupting N cycle

Places with high N (like near farms using fertilizer) are expected to have lower ______ _____

species richness

Human activity disrupting N cycle
Increased N runoff —> ______ —> ____ ____ —> “dead zones”

eutrophication
algal blooms

Why do algae blooms result in dead zones?

Algae bloom —> lots of phytoplankton —> phytoplankton death —> lots of _____ —> use up available ____ —> organisms die

decomposition
oxygen

aerobic/anaerobic

Nitrification is __________
Denitrification is __________

aerobic
anaerobic