Biol 208: Lecture 28 - Nutrient cycling

What is the RED FIELD RATIO?

106C: 15N: 1P

• Describes the elemental composition of our plants biomass (an approx. from phytoplankton)

Energy flow (Carbon flow) always carries nutrient atoms with it; when nutrients are in short supply, biomass creation is limited

With flow through food webs Carbon is RESPIRED and N+P are RECYCLED

Define nutrient pool + nutrient flux

Pool = amount of a particular nutrient stored in a portion or compartment of the ecosystem

Flux = Movement of nutrients between pools of an ecosystem

Phosphorus cycle:

• Where is it most + less LIMITING

• Where is the LARGEST POOL?

Most limiting = AQUATIC

Least = Terrestrial

Largest pool = Marine sediment + rock

Phosphorus is less likely limiting in terrestrial ecosystems

• What are 2 EXCEPTIONS

1. Very old soil eg. Tropical rain forest

2. Break down very slowly eg. Canadian shield

Phosphorus cycle

• What is P a key component in?

• What is the Ultimate reservoir of P on earth

• What is the active form

• What are 2 sources to make the active form of P available?

Ultimate reservoir = ROCK

• E (ATP), DNA/RNA + Phospholipids

Active = PO4-

2 sources:

1. Marine sediment → sedimentary rock → incorp into soils via weathering = Available for active cycling

2. Cell lysis + enzymatic cleavage of Organic dead matter → inorganic phosphate

Nitrogen Cycle

• what is N a key component in?

• Where is it limiting?

• What is the Ultimate reservoir of N on earth

• How is Biologically available N made?

Component in: Proteins, nucleic acid, chlorophyll _ hemoglobin

Limiting PRIMARY PRODUCTION in MARINE + TERRESTRIAL ecosystems

Ultimate reservoir = ATMOSPHERE (N2 gas)

NITROGEN FIXATION

What are the 3 methods of Nitrogen fixation?

1. Bacteria/ specialized organisms

2. Lightning

3. Industrial production of FERTILIZER (primary avenue)

ENERGETICALLY COSTLY

What are the three forms of Nitrogen that can be used?

NH4+ = Ammonium

NO2- = Nitrite

NO3- = Nitrate

Define:

• Ammonification

• Nitrification

• Denitrification

And how they all relate to each other

Ammonification = Release of N as Ammonium (NH4+) by all organisms (urine + feces) or decomposition

Nitrification = conversion of NH4+ into Nitrite (NO2-) — then quickly → Nitrate (NO3-)

• Change in OXIDATION STATE = releases E which allows nitrifying bacteria to create organic matter from CO2

Denitrification = Conversion of NO3- → N2 (dinitrogen gas)

• change in REDOX state allows bacteria to use this conversion instead of O2 to break down organic matter

• primary process in which N is LOST from ecosystem

How are Nitrogen transformations intricately linked to the carbon cycle?

1. respiration of organic matter:

   1. When O2 = not available Nitrate (NO3- → N2) replaces O2 as the energy yielding reaction in respiration (CH2O → CO2)

2. Organic matter Generation:

   1. Reduced (low O2) forms of N give off E when they gain O2 (NH4+ → NO3-). This E release allows CO2 to be fixed as CH2) = Equivalent of photosynthesis

Carbon Cycle

• Critical role of Carbon?

• Process of removal + return

• Long term pools

• Is carbon limiting?

critical role = global climate (CO2 + CH4)

Remove = Photosynthesis coupled with uptake of essential nutrients

Return = Respiration coupled with recycling of nutrients PO3- + NH4+

Major pools = Ocean Soil + Sedimentary rocks + fossil fuel

Define decomposition

• role?

• What controls the rate?

The process by which organic matter is broken down by microbes to nutrients (PO3- and NH4+) + released for uptake by primary producers + release CO2

• Rate of nutrient regen by decomp controls the availability of these nutrients which ties the production of organic matter

Controll:

• Moisture = Increases Decomp with increase moisture

• Temp = increase

• Matter composition = Increases with high N (nutrient) content

• Soil comp = increases with increased nutrients

What is AET?

Actual Evapotranspiration

• measure of the total amount of water that evaporates and transpires from a landscape

• Increases with increasing temp + precipitation (combined metric)