Can plants take up all of the CO2 in the atmosphere?

Think about the atmosphere around you.

What is it made of?

Earth’s Atmosphere

• 78% nitrogen• 21% oxygen• 1% argon• 0.038% carbon dioxide (CO2)• and traces of hydrogen, helium, and other

"noble" gases

What happens elements in the atmosphere?

Do they just stay in place or move around? Why?

Reactions

• The earth is a system where reactions that maintain life are fueled by sunlight.

• Almost all chemicals are fueled by living organisms

• Reactions are happening all around you, reactions that you cannot see!

http://www.chem.ufl.edu/~itl/2045/lectures/lec_3.html

Photosynthesis is a reaction• Photosynthetic

organisms capture the energy in sunlight and convert the bonds between carbon and oxygen in CO2 to weaker bonds that characterize life.

• All sorts of reactions can take place to store energy in the form of sugar molecules

CO2 in the atmosphere is increasing• Scientists have measured the CO2 in the air at Mauna Loa, Hawaii

What else do plants need to grow?

• Plants use light energy to change CO2 and water into food substances (sugars).

But, plants also need nutrients!

• Primary nutrients are nitrogen (N), phosphorus (P), and potassium (K)

• Secondary nutrients are calcium (Ca), magnesium (Mg), and sulfur (S)

Let’s look at one nutrient in particular. Why do plants need nitrogen?

• Nucleotides for DNA and RNA • Plants need these nitrogen compounds to

make amino acids, the base of proteins• We all need protein!

• But where do plants get their nitrogen?Photo of DNA base pairs above: http://cyberbridge.mcb.harvard.edu/dna_1.html

Nitrogen Fixation

• 1% comes from lightning • 99% is biological: bacteria can convert N2 into

NH3 using an enzyme called nitrogenase• Although a lot of bacteria and archaea can do

this, it is very energetically expensive to break this triple bond

Nitrogen can limit growth of trees

• Most plants grow under conditions of nitrogen deficiency.

• That means if you add nitrogen to plants, they have enough of all other nutrients to grow more.

• That is why farmers add nitrogen fertilizer to their fields!

Global Change

• Humans are increasing CO2 in the atmosphere• Some scientists have suggested that as the

concentration of CO2 rises, plants can take up in their biomass

• Will nitrogen fixation provide enough nitrogen to keep plants growing as CO2 increases?

Can plants keep up?

• You will be divided up into four focus groups:– (1) Why do we care about carbon dioxide (CO2) in the

environment? – (2) How are nitrogen and carbon related? – (3) How are nutrients added to ecosystems?– (4) How are nutrients lost from ecosystems? Can we run

out of nutrients?

• In Part II you will design an experiment to test the question: Will plants grow with increasing CO2?

Meet a Scientist

Michelle Wong is graduate student studying ecology and evolutionary biology at Cornell University in Ithaca, NY. She is interested in how humans impact the carbon and nitrogen cycle.

When she isn’t studying science, she likes to bake, rock climb, and spend time with friends and family.