Productivity Calculations SOLUTIONS



Productivity Calculations SOLUTIONS

Part I: (A) On the following graphs, draw IN PENCIL what you believe to be appropriate relationships for productivity in a forest environment. Focus on the general trend you would expect to see.

Productivity as a function of Temperature Productivity as a function of Precipitation

Part II:

A) This is the equation for photosynthesis: Write the equation for respiration:

6CO2 + 6H20 light( C6H12O6 + 6O2 C6H12O6 + 6O2 ( 6CO2 + 6H20 + ATP

B) Remember: NPP = GPP – Respirationplants

CALCULATE!

1. If the GPP for a patch of forest is 10 kg C/ m2-year, and the amount of carbon dioxide LEAVING the ecosystem

(don’t ask how we measured this!) is 5 kg C/ m2-year, what is the NPP?

NPP = GPP – Respiration

GPP = 10 kg C/ m2-year

Respiration (CO2 leaving patch of forest) = 5 kg C/ m2-year

NPP = 10 kg C/ m2-year – 5 kg C/ m2-year = 5 kg C/ m2-year

2. In the patch of forest in problem #1, how much energy is available in the primary producer level for herbivore

consumption? Assume 1 kg of carbon produces 10,000 kJ.

5 kg C/ m2-year * 10,000 kJ / kg C = 50,000 kJ/m2-year

3. Imagine we run an experiment on the algae Cladophora glomerata. We place equal amounts of algae into a light bottle and a dark (covered) bottle. We measure the dissolved oxygen in both bottles and find it is at 10 mg/L. We let both bottles sit for a week. In one week, the light bottle has a dissolved oxygen value of 11 mg/L and the dark bottle has a value of 5 mg/L. CALCULATE the amount of respiration, the NPP and the GPP in moles carbon per liter.

(Hint: 1 mg of oxygen is equal to approximately 3 x 10-5 moles of oxygen)

We know:

• Light Bottle has process of photosynthesis AND respiration

• Dark Bottle has only process of respiration.

So we can say:

• Light bottle measures NPP of algae (NPP = GPP – Rplants = Photosynthesis – Respiration of Plants)

• Dark Bottle measures respiration.

Starting with the dark bottle:

Start = 10 mg O2/L After 1 week = 5 mg O2/L

During the week, 5 mg O2/ L was consumed by RESPIRATION. This is…

5 mg O2 / L-wk * (3 x 10-5 moles of oxygen/ mg O2 )* (1 mol C / 1 mol O2 ) = 15 x 10-5 moles of C/L-wk

Then we work with the light bottle:

Start = 10 mg O2/L After 1 week = 11 mg O2/L

During the week, 1 mg O2/L was PRODUCED—both photosynthesis and respiration were going on, so this must be the NPP. This is…

1 mg O2 / L-wk * (3 x 10-5 moles of oxygen/ mg O2 )* (1 mol C / 1 mol O2 ) = 3 x 10-5 moles of C / L-wk

To calculate GPP:

NPP = GPP – Rplants

NPP + Rplants = GPP

3x 10-5 moles of C / L-wk + 15 x 10-5 moles of C / L-wk = 18 x 10-5 moles of C / L-wk

4. Imagine we run an experiment on a marine diatom. We place equal amounts of the diatom species in light and dark bottles, and measure their starting dry weight (take another “equal amount”) and dry it out. We end up with this data.

What is the NPP, GPP, and respiration of the species of diatom? Express your answer in grams per bottle.

|Week |Wet Weight |Dry Weight |

|Week 1 |14 grams |9 grams |

|Week 2 |19 grams |11 grams (light bottle) |

|Week 2 |12 grams |8 grams (dark bottle) |

SEE GENERAL STATEMENT OF LOGIC IN SOLUTION TO PART 3

Starting with the dark bottle:

Start = 9 grams biomass After 1 week = 8 grams biomass

During the week, 1 gram of biomass was consumed by RESPIRATION. This is: 1 g / bottle-wk

Then we work with the light bottle:

Start = 9 grams biomass After 1 week = 11 grams biomass

During the week, 2 grams of biomass were PRODUCED as NPP. This is: 2 g/ bottle-wk

To calculate GPP:

NPP = GPP – Rplants

NPP + Rplants = GPP

2 g/bottle-wk + 1 g/bottle-wk = 3 g/bottle-wk

Productivity Practice Problems

1. Which will produce more apples, Orchard A with 1037 BTU/m2/day of NPP, Orchard B with 773 BTU/m2/day, or Orchard C with 2,000 J/m2/day?

NPP really is equal to the amount of apples—remember we can define it as the amount of biomass/energy available for herbivores to consume. (For the nitpickers, you do need to assume that each orchard has similar species with similar amounts of flowers and then apples…but work towards making—and allowing yourself—to make and state simplifying assumptions to help you solve problems)

So, which has the greatest NPP?

Remember that 1,000 J is about 1 BTU, so 2,000 J is about 2 BTU’s.

That means ORCHARD A is the most productive

2. Which will give you more crops (by weight), a cornfield with a GPP of 5 kg/m2/harvest or a wheat-field with a GPP of 10 kg/m2/harvest?

You should not be able to answer this. GPP doesn’t tell you anything about production available for herbivores. You need to calculate in energy lost to respiration before you can answer this question.

3. Assuming GPP Forest A = GPP Forest B = GPP Forest C, which has the highest rate of respiration in it’s trees: Forest A, NPP = 1254 J/m2/day; Forest B, NPP =2157 J/m2/day; or Forest C, NPP = 779 J/m2/day?

If GPP is equal, then we can manipulate the NPP equation and solve.

NPP = GPP – respiration of plants; Respiration of Plants = GPP – NPP

This means that the smallest NPP corresponds to the largest respiration.

That is FOREST C

4. Which has a higher rate of respiration, Bog A with NPP = 300 g/m2/day or Bog B with NPP = 100 g/m2/day?

You should not be able to answer this. Without knowing GPP, you cannot talk about respiration. NPP = GPP – Rplants

5. If a forest has a GPP of 200 J/m2/day and 100 J/m2/day worth of carbon dioxide flow out of that forest, what is the NPP?

Simple formula plug in:

NPP = GPP – Rplants

Rplants = 100 J/m2/day worth of carbon dioxide (refer to equation)

GPP = 200 J/m2/day

NPP = 200 J/m2/day – 100 J/m2/day = 100 J/m2/day = NPP

6. If a dark bottle loses 1 g biomass/mL and a light bottle gains 5 g biomass/mL, what is the NPP? What is the GPP?

Remember, dark bottle = respiration only light bottle = respiration + photosynthesis = NPP

1) NPP = 5 g biomass/mL/week

2) To find GPP, manipulate NPP = GPP – Rplants ( ( GPP = NPP + Rplants

Rplants = 1 g biomass/mL/week and NPP = 5 g biomass/mL/week,

so GPP = 5 g biomass/mL/week + 1 g biomass/mL/week = 6 g biomass/mL/week = GPP

7. You start a light bottle/dark bottle measurement on algae Species X with 10 mg/L of oxygen in both bottles. You let the bottles sit for 1 week so that photosynthesis and respiration rates can be calculated. At the end of 1 week, you have 7 mg/L of oxygen in your dark bottle and 10 mg/L oxygen in your light bottle. What is the NPP, GPP, and respiration? Express your answers in moles of carbon per liter per week. Remember 1 mg of oxygen is equal to approximately 3 x 10-5 moles of oxygen.

1) Species X has consumed 3 mg O2/L/week by respiration in the dark bottle.

This is equivalent to:

3 mg O2/L/week * (3 x 10-5 moles of oxygen/ mg O2 )* (1 mol C / 1 mol O2 ) = 9 moles C / L-week = RESPIRATION

2) Species X has not produced any net productivity in the light bottle.

NPP = 0 mg O2 / L/ week = 0 moles C/ L-week = NPP

3) To calculate GPP, we again manipulate to find GPP = NPP + Rplants

GPP = 0 moles C/ L-week + 9 moles C/L-week = 9 moles C / L-week = GPP

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|0ºC TEMPERATURE 100ºC |

| High |

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|NPP |

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|Low |

|Low Precipitation High |

| High |

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|NPP |

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|Low |

|Note: In the field we |

|would probably not exceed |

|40 º C |

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