Gases and Nutrient Availability Impacts on Photosynthesis

What did the study analyzing how increasing [CO2] impacted yields between C3 and C4 plants reveal?

C4 yields didn’t increase with the change in CO2, indicating that C4 plants CARBON SATURATE

C3 yields increased with the increased [CO2] showing that they don’t carbon saturate

Why do C4 plants carbon saturate?

1) Doesn’t photorespire, so will tightly bind CO2 causing a “traffic backup”

2) C4 have a biochemical pump that captures CO2 in the mesophyll cells and returns to the bundle sheath cells. There are only 3-5 mesophyll cells per unit, so can only capture so much CO2 at a time.

3) Only have 10% PEP and 15% Rubisco, so limited rate of catalysis with increasing [CO2]

Why do C3 plants not experience carbon saturation?

1) 50% of proteins are Rubisco, so can quickly deal with increasing [CO2] concentrations despite photorespiration

2) CO2 diffuses into leaf cells. According to Fick’s law, increasing the concentration will increase the rate of diffusion.

What is Fick’s Law?

change [ ]/ change in distance

Increasing concentrations will increase the rate of diffusion

What did the FACE systems studies reveal?

FACE= Free Air CO2 Exchange

C4 soybeans are so close to seeing a yield increase with CO2

Other factors (water, nutrients, pests) can limit the yield increase we expect in C3 plants with changing [CO2]

How does still air impact photosynthesis?

Photosynthesis dramatically decreases when wind is restricted!

1) Wind decreases the distance that CO2 has to travel (Fick’s Law)

2) Still air forms a boundary layer that limits CO2 entering the leaf, which will limit photosynthesis

Which plant type wil have higher N use efficiencies?

C4

What impact do potassium levels have on plants?

Potassium is crucial for stomatal function (opening and closing stomates

How does phosphorous levels impact plant health?

Phosphorous has to enter for PGA to leave chloroplast. If PGA does not leave, photosynthesis will break down.

What are common symptoms for phosphorous deficiency?

Accumulation of starch in leaves, turning margins purple. Starch is made in the chloroplast with help from PGA