Productivity and the Carbon Cycle

1st Law of Thermodynamics: Energy is neither created or destroyed

2nd Law of Thermodynamics: Energy transfers result in a net loss of energy to entropy (disorder increases)

- Life (and ecosystem) directly contradict the 2nd law- Thus, require a constant inflow of energy

…and the process responsible for life (as we know it) on Earth

Photosynthesis is the starting point of the Carbon Cycle…

C3 photosynthesis, is the most common mode overall, and is especially important in temperate regions.

C3 photosynthesis, cont.

Two other modes, C4 photosynthesis and Crassulacean Acid Metabolism (CAM) have mechanisms that allow for photosynthesis without the risk of of water loss due to open stomates…

C4 photosynthesis, is a more (evolutionarily) advanced mode. Found (mostly) in grasses of arid environments.

C4 photosynthesis, utilizes a morphological adaptation (bundle sheath), and some unique compounds (eg. PEP carboxylase).

CAM photosynthesis, is found in mostly succulent plants (cacti; euphorbia; crassulacea)

CAM photosynthesis, uses similar chemical mechanisms as C4, but does not have the same morphological adaptation. Key is timing. Stomates open at night, CO2 is stored as malic acid…stomates close in the day- malic acid reconverted to CO2.

How does this

Relate to this

What happens after carbon is captured by plants is called “carbon allocation.” Basically, it is accounting for energy transfers in the 1st trophic level of the food web. How does the plant use the energy?

Scaling back…

Respiration and photosynthesis are oppositional processes in the carbon cycle- photosynthesis captures carbon, respiration uses the energy and releases carbon in the atmosphere. But humans have gotten involved, too, by burning long-stored carbon to power our Powerpoint projectors and I-Pad Touch 4 Gs, and other things

We track carbon flow using these ideas:GPP; NPP; NEP

One important question for ecology is-

what regulates carbon storage?

Ecosystems are not equally productive. There is clear variation. That variation is related to things that drive the the carbon cycle at a broader scale- across ecosystems what are the regulatory processes/factors?

Precip and Temp!

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Evapotranspiration is a general measure of energy flow into the system- water being evaporated and transpired by plants.

As evapotranspiration increases, generally, there is more productivity in the ecosystem

Global patterns of (terrestrial) productivity

- Ecosystem productivity is variable across broad geographic scales… related to precipitation and temperature.

- What are the most important drivers of productivity at more local scales?

Soil fertility...

Why “aboveground”?

Soil fertility...

In the ocean, depth is important...

Productivity response to particular nutrients is variable….

And for a single nutrient, response depends on existing levels in the ecosystem. Adding phosphorus makes the productivity in bays go down?! Why?

Global patterns of ocean productivity

Productivity is related to variability in the climate

Allocation changes through time in trees

Allocation changes through time in trees

General rule: only 10% of energy stored in any trophic level is passed on to the next level during consumption

I am an ecologist…

Productivity and the Carbon Cycle