Global Productivity and CO2 Responses

Question 1

What biome has the best net primary productivity?

Answer 1

Tropical forests are the best producers as they have no winters, warm, lots of water etc

Question 2

What biome is the least productive?

Answer 2

Tundra

Question 3

When is the enzyme Rubisco more efficient?

Answer 3

At greater CO2 concentrations as there is less photorespiration

Question 4

What is the CO2 fertilisation effect?

Answer 4

More CO2 causes more photosynthesis and more growth

Question 5

What photosynthesis does rice undertake? What happens if CO2 concentration increases?

Answer 5

Rice has C3 photosynthesis

Growth increases as CO2 increases

Question 6

How much of global CO2 uptake is by C4 photosynthesises?

Answer 6

23%

Question 7

What do FACE experiments stand for? What are they?

Answer 7

Free Air CO2 Enrichment

Leaky pipes leak CO2 into the atmosphere so plants inside the ring grow in high CO2 concentration environments

More natural experiment as only controlling CO2 concentration

Question 8

What did the FACE experiments show?

Answer 8

When light saturation is increased, don’t get much extra growth in C4 plants

Sorghamn is an important C4 crop and is barely responding to increased CO2 concentration

Rice and wheat (C3) are barely increasing

Question 9

What was the average crop yield stimulation in the FACE experiments?

Answer 9

17%

Question 10

Where will carbon sequestering increase the most with increasing CO2?

Answer 10

Global average of a 12% biomass increase

Largest increase in forest systems (13%) and less in grasslands (10%)

More productive systems are more responsive to increased CO2

Question 11

Why is the increased carbon storage still less than what the FACE experiments suggested?

Answer 11

Plants may photosynthesis more but that does not mean biomass increases

May not be enough nutrients to increase biomass

Trees may already be full grown/mature so won’t grow anymore

If no nutrient deficiency, plants would uptake 2x as much carbon from the atmosphere

Question 12

Where did plant biomass increase between limestone and acidic grasslands as CO2 increased?

Answer 12

16% increase in biomass in limestone ecosystem

Reduced plant biomass in acidic grasslands

Question 13

What causes the difference in biomass in the limestone and acidic grasslands?

Answer 13

In limestone:

Phosphorus in plants and microbes is not changed by increasing CO2

In acidic:

More phosphorus in soil microbes vs plants

Increasing CO2 causes soil microbes to get more ‘limiting’ phosphorus nutrient

Less phosphorus for plants to use and grow